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screen printing => Separations => Topic started by: Dottonedan on April 02, 2011, 11:04:03 PM
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When choosing a halftone shape when outputting films, you might ask yourself "Why would we use ellipse dot shape over a round dot?"
Using one or the other does not impact high end simulated process as much as it does lower halftone count that result in larger dots. It makes a difference in the visual appearance if your using lower halftone counts and printing a limited number of colors that lay on a contrasting color.
Using black ink on a white garment is a good example of that. The larger the dot, the more obvious the issues become. See the examples below to help explain.
You can see here that you only get about 8-9 dots of transition using (ROUND).
(http://www.dot-tone.com/graphics/images/stories/Separation_Examples/training-dot-10x10-80%25-0-0degrees-final.jpg)
Here you can see that you get about 19-20 dots of transition using (ELLIPSE).
(http://www.dot-tone.com/graphics/images/stories/Separation_Examples/training-ellipse-10x10-80%25-0-0degrees-final.jpg)
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I always thought ellipse was used in order to prevent moire.
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I always thought ellipse was used in order to prevent moire.
Ditto.
EDIT: I guess I should add that for the last 8 or ten years the only time I break out the elliptic dots is for 4 color process which I rarely ever do any more. I started using round dots and the same angles somewhere in the automated separation program (actions) days .... I think it was Color Crunch that got me started on the roundy kick. I tried 'em ALL at some point.......
Strange... Just last week I was outputing some film and clicked on ellipse... just for old times sake.... you know what? IT WORKED! ;)
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I have done very little with half toning but realize that it is now time to start pushing some of my printing. I love to learn things like this.
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Ellipse dots shapes are an added benefit to improving a 4 color process print (simply because of the smoother transitions) when using halftones. Not much mare to it than that.
It has very little to do with improving moire. If you are going to have moire issues, it's because of other issues the effect moire more directly and in larger, more impactful ways. Your are about 2-3% less likely to have moire issues... if you used elliptical dot shapes. Thats a guess at that specific number, but it's to illustrate how little the dot shape actually plays a role in improving moire.
The original maker of Color Crunch (Charles facini) and I had some pretty good conversations on this topic about 12 years ago and we were in agreement. 4 color process is done well with the same screen angle for all mesh. People love the "rosette" theory that you need a good rosette to create better color blends. Not true. Someone "recently" also showed me where a guru who wrote a book on the subject included that rosette pattern are needed to created better blending in CMYK. That guy made a mistake. :) Process inks are (translucent) inks and "require" the merging of dots to create other colors. Rosette patterns are formed due to an exact measurement of cross alignment thus forming this "rosette" shape. This "pattern" does not improve blending any more than a single screen angle does. If fact, it probably interferes with blending in a very small way more than it does benefit.
Tossing in the added variables of aligning "different' screen angles hoping that you don't get any moire is just compounding your potential problems. WHY?
Streamlines that process and use all of the same angles.
He's another thing to consider, Will all of the jobs that I do and the places I have worked outputting films/color separating for company's, it's been working for them all this time...without one complaint about my using all of the same screen angles. Some of these designs the company's have actually ran hundreds of thousands of shirts from. Very few were in that large of a number, but you get my point.
Another thing that gets me is that people will not blink an eye if I say sure, use a single screen angle of 22.5 degrees on all 10 screens of a (simulated process job). The moment I say to use that same screen angles with 4 color process. THEY SHREEK as if I had just cussed out Jesus himself. WHA?
LOL. This business is funny stuff.
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On the dot note... I use an angle of 26 (22.5 was my angle of choice for a long time... to be honest I forget why I changed it) for all screens and for the last 5 or so years have been outputting at 45 dpi. It works for MOST things that pass through my shop. I still keep some 305 mesh around for the occasional "high end" stuff that rolls my way. I find with a little larger dot, a little lower mesh count and the elimination of process inks (for the most part) things seem to be less of a challenge for my press operators (me a lot of the time) to produce great images. And side by side I have found the customers just really can't tell the difference. The easier it is for me, the better ;)
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Tossing in the added variables of aligning "different' screen angles hoping that you don't get any moire is just compounding your potential problems.
I think you'll agree that using a single angle is OK, but get one of the screens slightly misaligned and the moire is horrible. Rosettes are more robust to misregistration. In addition, I think that the colours are more consistent with rosettes, it's less sensitive to which screen is printed first because the colours aren't on top of one another. Are you printing shirts? They tend to be more tolerant of same angles, don't try it with graphics printing!
JMHO
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Most all of us here are shirt printers. We love other types of printing as well but 99% of us are talking about printing shirt. With that said,
I think you'll agree that using a single angle is OK, but get one of the screens slightly misaligned and the moire is horrible.
No actually, I don't really agree. I hhope I'm not sounding bold or arrogant, but speaking specifically in terms of printing on apparel, I don't get moire in my prints from angles (at all). when ever I've received any feedback from customers about moire, it's been due to screen mesh distortion, emulsion thickness, RIP processing etc. Never any moire from screen angles. I know this from first hand experience. I've done allot of printing 4 color process and sim process in both different angle and all same angles over the last 24+ years.
For me, all the same works best. no question. Now, keep in mind, I don't just do this for myself. I am a separator. I separate jobs out for about 5 shops a day on average. About 3 out of 10 jobs are for process printing and I set the files up for all same angles. Now, for you...and what you do with file prep and/or your color separation techniques. It may work best for you using the rosette patterns and then some just like the look of the pretty rosette pattern. :)
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I disagree with everything which has been said. ;D
In screen printing, it is the knit of the fabric which causes the greatest moire. This has nothing to do with dot shape, but a simple interaction of dots printed on a textile. As dots cross the textured field of the textile, fine dots will fall into the valley between the threads of the knit, where the ink has no fabric to print. Or the dot will hit the summit of a knot in the textile and print 110%!
In printing a "dot" is the smallest reproducible shape which the washout process can hold. The "ellipse" tends to cross the valley of the textile knit, by bridging a gap unidirectionally.
Angles like 0%, 90%, 180% OR 270% is just asking for a problem with the alignment of the halftone to the alignment of the knit.
My favorite spot function starts as a dot as small as is reproducible, then grows into an ellipse, then grow into a uni-directional "line screen". A line screen as opposed to a halftone dot, does not moire. Dots based halftones do moire. The spot which starts as a dot, should grown into an ellipse, which transforms into a line.
Beyond theory, a 45 LPI "line" halftone is just easier to print than a 45 LPI "round dot" or "ellipse dot" halftone. A line screen at anything other then inline with the shirts knit will not moire, not in 1 color, not in full color.
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Haha. I was just telling Pierre that I think The Duke is in town. ;) lol. Good to see you here. Stay clean, brush your teeth and we will all have fun.
As usual, your way with words and how you so eloquently dance around the language and science of printing is very inspiring. While I am often impressed by your wisdom, I do not agree with "all" of what you say.
A line screen as opposed to a halftone dot, does not moire.
I am not 100% sure that what I am seeing as a 'line screen" is the same as what you are referring to. Please, if you will, maybe post up a snap shot example. I double Yorkie Dog dare ya.
Line screens, halftone patterns, be it ellipse or round can create moire. The simple fact of taking any repetitive line element and crossing that with another repetitive line element at an angle can cause moire. Take a wide open mesh like the screen you put on your screen door. Lay another that is identical in mesh count across it and it too will dance with moire patterns. It's a "line" pattern. The mesh threads are lines that weave in and out, yet still form a line. Thats a simple example.
I do agree that I have seen where the mesh of a garment can interfere with the halftone pattern. It's actually pretty rare and not easily achieved but can happen it you try hard enough. I mean, you have to be pushing the envelope pretty hard in order to have the weave cause issues. I've seen in happen in high line counts like 70lpi in small percentages like 5% halftone or something. When that happens, just adjust the screen angle a tad or decrease the line count a few degrees can it goes away.
I do remember you mentioning this same issue before. I believe you were suggestion that it make snot benefit to print a 60 line screen on apparel as the dots in the highlight areas are too small for the hills and valleys of the apparel thread weave. I disagree here as well. Especially with everyone printing films out on these digital printers. The dots of a 60lpi are not 100% accurate. Close, and some farther away from close but still usable. Who cares if it's really a 5% of a 60 lpi. AS long as it works. Pierre for example has been printing 65 line screen sim princess all at the same screen angle of 22.5 with no mesh interference and not garment weave interference. I do remember one job we did where in a 65 line screen we were pushing it with black ink on a white ground printing over top of some very light blues. Those stood out a tad more and did show some "unwanted patterns" in the highlight areas of the print. At that point, we could tell for sure if it was the weave or the mesh. Pierre has increases his mesh quality greatly since then. No issues with 65lpi on 330 mesh.
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Picture of a line screen:
http://www.positivityltd.co.uk/halftones/Positivity-Ellipse-Line.jpg (http://www.positivityltd.co.uk/halftones/Positivity-Ellipse-Line.jpg)
this one is actually a long axis ellipse that naturally becomes line like.
The 'no-moire' thing is because if you take a 45 degree round dot and a 135 degree they will be identical but a 45 & 135 degree line combo will give a really robust rosette. So if you rotate a circle 90 deg, it's the same, a line isn't.
It doesn't mean that lines can't moire - drive on a motorway with a pair of fences beside and you can see lots of moire, but there are twice as many angles that won't moire.
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Hmmmmm. Well that's interesting. I like different patterns. Never been exposed Yo someone using a real "line pattern" before. Ive seen them but only in the old school "supply closet" where we kept the verityper, thr press type and various halftone mezzotints on films.
Do you actually use such a beast? What type of print process and can you give an example of when you might use something like this? Just curious. Hoping to find something new again.
Thanks
Dan
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Lines are good in that they give very tight rosettes but they need a custom icc profile because they give a colour cast depending on which colours you pair (effectively you have a pair at 18 & 108 and a pair at 71 & 161 degrees)
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Here is an example, as best i recall, 55 lpi-25% tint, heavyweight t-shirt, manual press.
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It doesn't mean that lines can't moire - drive on a motorway with a pair of fences beside and you can see lots of moire, but there are twice as many angles that won't moire.
That is not a moire. That is a phenomenon known as strobing. This happens when 2 angles match, so with slight motion if one piece of film, the one below it can either be seen or not be seen. If one of the fences were oriented at a different angle, it would not be strobing.
The file Positivity-Ellipse-Line.jpg is an ideal halftone. The dot should start out as a round dot as small as is reproducible, then grow into an ellipse till the ellipses connect, then grow int a wider line. The problem with the standard line halftone is that the ellipse is too small to repeat until after the line connects.
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All interesting reads. Love it.
Here is an example, as best i recall, 55 lpi-25% tint, heavyweight t-shirt, manual press.
Great picture. Thanks for taking the time to post it. I still don't really think your issue here is garment weave. Are you sure that you did not already have weaker areas in your films? I've seen some RIPS provide this effect straight out of the film printer depending on a few things. 1, a weak rip system. Some are worse than others. 2, Rollers need cleaned and can be skipping so to speak. I'm not claiming to be an expert in those areas, but thats what I've seen.
I say that, because really, you should bot be seeing stronger and weaker dots (due to the weave of a garment) at 55 lpi-25% tint. If so, then I would suggest that you have other issues outside of the weave factor. When looking at it, it may make you think it's the weave (by appearance only).
A 55 lpi-25% tint, is actually a pretty robust percentage. I would venture to say that at a 25% tint, you should not even get weave interference at 65 line screen. 5% on a 65 line screen is more like the range for weave interference from what I've experienced. I could be wrong. I'm open to proving me wrong. It's educational.
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I can make them round/ellipse/line, it just takes a little playing with the postscript definitions.
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I once tried to create my own postscript halftones using my logo. I never really took the time to complete it. Would have been cool though.
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I could be wrong. I'm open to proving me wrong. It's educational.
I'm not proving anything to anyone. If you care, look the next time you print a halftone on a heavyweight shirt. Look real close.
Every dot printed on a textile is effected by the knit.
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I don't doubt you really. Just never experienced it that way myself.
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I prefer the four angle set. It holds better shadow detail and is more forgiving when slightly out of register.
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It's interesting how very different our preferences can be. I don't doubt that these other angles work for others. For me and my customers thus far, we don't have any issues with miss aligned angles....that I am aware of. Nobody makes me aware of any issues. I do see the results tho. For example, you can find a CMYK job I separated here on this forum. I think it's in Gallery and posted by Pierre from Blue Moon. It was all done at 22.5 in straight process. The interesting part is that it is riddled with areas of solid consistent colors. These are typical areas where if you are going to see moire or mesh interference.
It's a cartoon in CMYK as well as having an underbase for medium colored garments.
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I agree Dan, we all do things differently. I guess it is just what works, or what we have learned over the years, as to how we approach the execution of our jobs. Discussing how we do things differently and what works for us is what I am here for.
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I agree Dan, we all do things differently. I guess it is just what works, or what we have learned over the years, as to how we approach the execution of our jobs. Discussing how we do things differently and what works for us is what I am here for.
YIIEEEPEEE! I keep thinking about it and wandering if I am missing something by sticking to the same angles (sorry Dan!). Have you tried to do the same print with both and compared?
Could it be that one works better for some and the other is better for the rest?
I know Dan is firmly in the 22.5 clan and the other person I respect very much (His royal highness) is hard core rosette supporter. I have been printing 22.5, and thanx to Dan doing rather well, so there is no question that some remarkable prints can be produced by using the same angles, but I should really try the rosette just to see what happens.
pierre
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I will point out that 'everything at 22' is almost unique to the tshirt industry!
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I will point out that 'everything at 22' is almost unique to the tshirt industry!
I work in Flexo printing Co. and we use some weird numbers for our angles. Something like 7 for Cyan, 28 Magenta, 35 Yellow and 51 Black. Any other screened color should not be any of those before mentioned angles.
Do not ask me why those exact numbers.
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I respect very much (His royal highness) is hard core rosette supporter.
If you mean Coudray, well yeah he is.
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I believe Pierre is referring to "The Duke of York" aka Yorkie to these forums.
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I work in Flexo printing Co. and we use some weird numbers for our angles. Something like 7 for Cyan, 28 Magenta, 35 Yellow and 51 Black. Any other screened color should not be any of those before mentioned angles.
Do not ask me why those exact numbers.
The reason why, is the anilox roller has a 45 degree angle. An anilox roller is what transfers the ink onto the flexo plate. Because the ink is being transfered at a 45 degree angle, it could moire or strobe with the halftone angles of the dots etched into the flexo plate. Since the anilox was 45, every other angle needed to rotate.
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Orion meet The Duke(ie) of York(ie)!
That last answer is why we missed him so much!
Your Royal Highness, can you under any circumstances (in your opinion) see where a 22.5 would be a better choice than a rosette?
pierre
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RIPs without 'accurate screening' or halftoned in an application can only use a limited set of angles (the printer can only produce angles that are a whole number of pixels in the X&Y axes, so you can't have 20.5 x 20.5 pixels for instance) Some angles don't exist at all, 15 degrees turns out to be irrational, it cannot be described by dividing one integer by another. You will always get 15.1 degrees, 15.02, 14.96 etc.
If you get the angles even slightly wrong you can get moire.
Having a single angle overcomes this problem.
The application ICC profile is set up to expect rosettes, you may see a colour shift with single angles because some colour will be masked more than others.
Slightly different misregistration on the print will expose different colours which will give a different effect, you might have more cyan or magenta exposed. It will be prone to moire if misregistered.
Rosettes are less susceptible to these variations.
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I don't see it yet. I'm open to change but but thuis far you don't have me convinced.
you may see a colour shift with single angles because some colour will be masked more than others.
Slightly different misregistration on the print will expose different colours which will give a different effect, you might have more cyan or magenta exposed. It will be prone to moire if misregistered.
Each issue here that you covered also equally applies to using a a rosette pattern.
Slightly different misregistration on the print will expose different colours which will give a different effect,
Same for Rosette.
you might have more cyan or magenta exposed.
Same for rosette.
It will be prone to moire if misregistered.
Same for rosette but in my opinion, even more with rosette.
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I don't see it yet. I'm open to change but but thuis far you don't have me convinced.
You don't need convincing Dan, just the people that output film and print your seps do. :D
I have seen prints using a single angle set that look great, but I prefer the four.
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I don't see it yet. I'm open to change but but thuis far you don't have me convinced.
you may see a colour shift with single angles because some colour will be masked more than others.
Slightly different misregistration on the print will expose different colours which will give a different effect, you might have more cyan or magenta exposed. It will be prone to moire if misregistered.
Each issue here that you covered also equally applies to using a a rosette pattern.
Slightly different misregistration on the print will expose different colours which will give a different effect,
Same for Rosette.
you might have more cyan or magenta exposed.
Same for rosette.
It will be prone to moire if misregistered.
Same for rosette but in my opinion, even more with rosette.
No, with 'same angles' you have dot on dot, if you move it slightly the misregistered colour will show like an untrapped underbase. With rosettes, the colours avoid each other so if you have a tiny misregistration, they still aren't any different. With same-angle you have black on yellow on magenta on cyan on white, with rosettes you have mainly one colour on white?!?
Lithoprinters and screenprinters have been using rosettes for about 100 years, I don't think that they would have missed the same-angle route if it's superior?
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The attachment was created using traditional angles verses all the same angles.
the top 2 images use a rosette halftone, which no matter how the color channels shift, the image retains the same hues.
The bottom 2 images use the same halftone angle. Because the dots are similarly arranges, small shifts of the halftone will reveal different dots. For process color, there is a bit of no harm, fowl, because the ink is transparent and the ink spreads, so the end result on a shirt is less dramatic than the image.
One of these days, i should update this to show line screens.
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The attachment was created using traditional angles verses all the same angles.
the top 2 images use a rosette halftone, which no matter how the color channels shift, the image retains the same hues.
The bottom 2 images use the same halftone angle. Because the dots are similarly arranges, small shifts of the halftone will reveal different dots. For process color, there is a bit of no harm, fowl, because the ink is transparent and the ink spreads, so the end result on a shirt is less dramatic than the image.
One of these days, i should update this to show line screens
I'm trying to see the enlightening concept of the picture example. What is it to show or indicate?. The top is rosette and the bottom is single angle. Got it. I see the strobe your talking about (if i move my window scroll up and down).
Is that what your saying is the reason not to use them? if they miss register they strobe?
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No, with 'same angles' you have dot on dot, if you move it slightly the miss-registered colour will show like an untrapped underbase. With rosettes, the colours avoid each other so if you have a tiny miss-registration, they still aren't any different. With same-angle you have black on yellow on magenta on cyan on white, with rosettes you have mainly one colour on white?!?
Lithoprinters and screenprinters have been using rosettes for about 100 years, I don't think that they would have missed the same-angle route if it's superior
No, with 'same angles' you have dot on dot, if you move it slightly the miss-registered colour will show like an untrapped underbase.
emmmmm. I don't think so. I've not experienced that. Remember, we are talking about tee shirts. Thats my only long term experience. I know shirt printing. Now, with that said, I also am not unfamiliar with flat stock printing. I did work in a sign/poster screen printing shop that did 4 color process. I separated the art. I know that registration shift and dot spacing is much more visible with that. But, we are not talking about what effects are more visible with flat stock. I'm not saying that you are only referring to flat stock or any other method outside of tee shirts, but you are on a tee shirt forum.
With rosettes, the colours avoid each other so if you have a tiny miss-registration, they still aren't any different.
It's interesting that you think this. I don't agree and can't comprehend the logic behind the statement but... who am I? I'm not scientist of the rosette.
With same-angle you have black on yellow on magenta on cyan on white,
Yes and no. What you have is the exact same "color content in it's intended location based on percentage" but just put down in two different methods ending up with the same color result. One, being the rosette that offers 3 more interfering variables not to mentions an odd looking "rosette" pattern within my design, creating this unwanted "pattern within my art, textures and patterns". Yuk.
Lithoprinters and screenprinters have been using rosettes for about 100 years, I don't think that they would have missed the same-angle route if it's superior
C'mon now. When anyone ever thought of printing halftones, they were thinking of doing it for what? Paper. So when people started printing on paper using a screen printing technique, they used the rosette pattern because why? Because that is what they were familiar with. "Hey Tom, What screen angle should we use when printing four color process using this screen printing method? Oh, well, various angles of course, so they don't interfere with each other". They followed what everyone started doing....but it's not needed for tee shirts. Let it go. :)
Having a shift of any kind, showing some additional white space...or additional cyan or, or...is similar to the impact on your choices of using to much or too little amounts of lets say...black to use to replace amounts of the other ink. The choice depends on the art, the technology, the substrate and the ink type in use. As you know, I am referring to the processes called under color removal, under color addition, and gray component replacement. Typically used to decide on the final mix; different CMYK recipes will be used depending on the printing task. These are all "choices" for CMYK printing and ALL have some effect on printing the art (just like choosing to print a rosette or a single line screen, {for tee shirts}, you should choose your under color removal differently from flat stock printing as well.
We do not use the same settings as does an off set or flat stock printer. Why is that? Because our substrate is much different and we don't need to do certain things or we don't want the additional variables if we don't need them. This is why, for the most part, I don't follow the litho world. I am not a peach, I am an apple, so says me.
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No, with 'same angles' you have dot on dot, if you move it slightly the miss-registered colour will show like an untrapped underbase. With rosettes, the colours avoid each other so if you have a tiny miss-registration, they still aren't any different. With same-angle you have black on yellow on magenta on cyan on white, with rosettes you have mainly one colour on white?!?
Lithoprinters and screenprinters have been using rosettes for about 100 years, I don't think that they would have missed the same-angle route if it's superior
No, with 'same angles' you have dot on dot, if you move it slightly the miss-registered colour will show like an untrapped underbase.
emmmmm. I don't think so. I've not experienced that. Remember, we are talking about tee shirts. Thats my only long term experience. I know shirt printing. Now, with that said, I also am not unfamiliar with flat stock printing. I did work in a sign/poster screen printing shop that did 4 color process. I separated the art. I know that registration shift and dot spacing is much more visible with that. But, we are not talking about what effects are more visible with flat stock. I'm not saying that you are only referring to flat stock or any other method outside of tee shirts, but you are on a tee shirt forum.
With rosettes, the colours avoid each other so if you have a tiny miss-registration, they still aren't any different.
It's interesting that you think this. I don't agree and can't comprehend the logic behind the statement but... who am I? I'm not scientist of the rosette.
With same-angle you have black on yellow on magenta on cyan on white,
Yes and no. What you have is the exact same "color content in it's intended location based on percentage" but just put down in two different methods ending up with the same color result. One, being the rosette that offers 3 more interfering variables not to mentions an odd looking "rosette" pattern within my design, creating this unwanted "pattern within my art, textures and patterns". Yuk.
Lithoprinters and screenprinters have been using rosettes for about 100 years, I don't think that they would have missed the same-angle route if it's superior
C'mon now. When anyone ever thought of printing halftones, they were thinking of doing it for what? Paper. So when people started printing on paper using a screen printing technique, they used the rosette pattern because why? Because that is what they were familiar with. "Hey Tom, What screen angle should we use when printing four color process using this screen printing method? Oh, well, various angles of course, so they don't interfere with each other". They followed what everyone started doing....but it's not needed for tee shirts. Let it go. :)
Having a shift of any kind, showing some additional white space...or additional cyan or, or...is similar to the impact on your choices of using to much or too little amounts of lets say...black to use to replace amounts of the other ink. The choice depends on the art, the technology, the substrate and the ink type in use. As you know, I am referring to the processes called under color removal, under color addition, and gray component replacement. Typically used to decide on the final mix; different CMYK recipes will be used depending on the printing task. These are all "choices" for CMYK printing and ALL have some effect on printing the art (just like choosing to print a rosette or a single line screen, {for tee shirts}, you should choose your under color removal differently from flat stock printing as well.
We do not use the same settings as does an off set or flat stock printer. Why is that? Because our substrate is much different and we don't need to do certain things or we don't want the additional variables if we don't need them. This is why, for the most part, I don't follow the litho world. I am not a peach, I am an apple, so says me.
Please look at the pictures posted by Yorkie, the lower pictures show a greater difference in colour and greater moire. Thanks Yorkie, I was going to produce similar pictures but frankly I couldn't be arsed ;)
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I'm trying to see the enlightening concept of the picture example. What is it to show or indicate?. The top is rosette and the bottom is single angle. Got it. I see the strobe your talking about (if i move my window scroll up and down).
Is that what your saying is the reason not to use them? if they miss register they strobe?
At the scale of halftone dots, there is no way to ever have "perfect registration".
I encourage everybody to buy themselves a loupe. My favorite is a Paragon 10x loupe. I've owned mine for over 30 years. What i like about the paragon, is that it folds and can be carried in a pocket full of keys and change. In order to succeed in printing halftones, a loupe is your best friend. 10x is enough magnification to see what needs to be seen, but not too much.
(http://www.peakoptics.com/images/OPT-PAR.jpg)
I believe what i do about halftones, because i have seen it with my own eyes. Don't take my word or anyone else's. LOOK YOURSELF! My claim is that when the same LPI and angle is used by 2 screens, that the dots of one can hide behind the dots of the other or not hide, depending on registration. I also claim that across the entire image, that the dots will be doing one thing on one part of the shirt and something else somewhere else. With rosettes, it will be doing rosettes everywhere, regardless of registration. It makes no difference if the registration creates one form of a rosette one place and a different one somewhere else, the rosette is a rosette. If you look carefully at the image i uploaded, you can see the position of the rosette actually shifts, but still remains a rosette.
In an earlier post i mentioned textile moire. Most times that one color prints with a moire, it is a combination of the halftone to the textile. If textile moire were not an issue, round dot halftones would be preferred to ellipses. The reason i believe people use all matching angles is that the textile moire causes problems which are worse than the effects of strobing. At 22.5 degrees, elliptical dots, the fabric is least likely to moire with the halftone. If it works for 1, it works for all and as i mentioned in the prior post, the textile has other effects on ink which go past angles and dot shape and into things like spread and absorbability.
Now everybody, grab your loupe and take a look!
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At the scale of halftone dots, there is no way to ever have "perfect registration"
I encourage everybody to buy themselves a loupe. My favorite is a Paragon 10x loupe. I've owned mine for over 30 years. What i like about the paragon, is that it folds and can be carried in a pocket full of keys and change. In order to succeed in printing halftones, a loupe is your best friend. 10x is enough magnification to see what needs to be seen, but not too much. ([url]http://www.peakoptics.com/images/OPT-PAR.jpg[/url])
I would not be bold enough to pretend to know anything about halftone printing if I didn't know anything about a loupe.
(http://www.dot-tone.com/graphics/images/stories/my_site_images/loupes-many.jpg)
I believe what i do about halftones, because i have seen it with my own eyes. Don't take my word or anyone else's. LOOK YOURSELF!
I have.
My claim is that when the same LPI and angle is used by 2 screens, that the dots of one can hide behind the dots of the other or not hide, depending on registration.
Yes, Same for rosette.
I also claim that across the entire image, that the dots will be doing one thing on one part of the shirt and something else somewhere else. With rosettes, it will be doing rosettes everywhere, regardless of registration.[/quote] You got me baffled on this. I don't agree.
It makes no difference if the registration creates one form of a rosette one place and a different one somewhere else, the rosette is a rosette.
Hmmmm.
If you look carefully at the image i uploaded, you can see the position of the rosette actually shifts, but still remains a rosette.
I don't know about everyone else, but I clicked on that pic and it blew up and became even blurrier to me than when viewed at the snap shot size. I can't see any "detail" in it to tell anything about the dots.
In an earlier post i mentioned textile moire. Most times that one color prints with a moire, it is a combination of the halftone to the textile.
again, I might be slow some how when it comes to comprehending what you are saying here. None of this is my experience and I've got allot of it. My customers and shops where I've worked have printed FINE halftones of black ink on white tees allot...and with no moire issues. My typical halftone is 55lpi with 22.5 degrees using an ellipse dot shape. We can even go 60lpi safely with most customers. Now, I can use a round dot or even a square if anyone wishes but with no moire on any of them.
If textile moire were not an issue, round dot halftones would be preferred to ellipses.
ummm. see pic at beginning. "There is a reason it is not the "preferred dot". The effect in the initial post here does happen no matter what substrate. It's not the textile that effects this.
The reason i believe people use all matching angles is that the textile moire causes problems which are worse than the effects of strobing.
Moire is not all that common. If you are getting moire, it's because you're making a mistake in your process. Not what shape your dot is...and it's not always "at what angle" as a reason for moire but most likely, it's to do with all of those varying angles. Keep those boogers at the same angle and it's golden. If that were the case, someone who does have good working varying screen angles for CMYK would not experience moire...and we all know that moire can happen at any time if you do not have everything in tight.
At 22.5 degrees, elliptical dots, the fabric is least likely to moire with the halftone. If it works for 1, it works for all and as i mentioned in the prior post, the textile has other effects on ink which go past angles and dot shape and into things like spread and absorb-ability.
Ok. I'm with ya here. I agree. We are now firing on the same brain waves.
Now everybody, grab your loupe and take a look!
Been there. Done that. Got the tee shirt. :) Haha. get it? Got the tee shirt? oh brother.
You know, what really bothers me is not that you 2-3 agree or don't agree. It's that you think that the old way is the only way or the "right way". You know how to determine good art? It's based on making the sale. Good art to one is an opinion.
Good halftone angles apparently is an opinion also. If a single angle didn't work, or wasn't good enough or isn't the right way, then how is it that so many people bought hundreds and hundreds of thousands, no. Scratch that. ....42000.00 units per week and 2.2 million per year (conservative calculation) on average, using my single line screen of using my 22.5 degrees? not to mention winning 2nd place in Sim process using a single line screen angle? Just asking.
I think I'll stick with my 22.5's ::) You can't argue with smooth production and big money.
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So the four angle set does not work? I guess millions of people are gonna want their money back that they paid for their shirts when they find this out. No one said you were wrong Dan, sorry if we offended you in any way. ::)
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My take when I look at Dukes example I do not see the second rosette as any blurrier at all, and all the colors look the same no shift.
The bottom set has a distinct difference between the two and not for the good. Thats my opinion for what its worth.
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Sim process is done with opaque inks, the difference in colour with misregistration is going to be greater?
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So the four angle set does not work? I guess millions of people are gonna want their money back that they paid for their shirts when they find this out. No one said you were wrong Dan, sorry if we offended you in any way. ::)
To imply that I am saying it doesn't work, would be putting words in my mouth in hopes to do the ole switch-er-oo. No. It does not mean that is does not work. That would be ridiculous to say. In fact, if you go back into my post (Don't bother, it's not there). You would see that I never said that at all. I am simply saying, don't bank on the old "rosette" theory as a MUST HAVE. in fact, all I am saying is that. "For tee shirts, using multiple screen angles and desiring the "rosette" pattern is not needed for screen printing on tee shirts. and I prefer the single line screen. It's you guys that are desiring to show me different and well, I've not seen any real proof at all yet. I am open for doing it the best way and the easiest way. Sometimes those two aren't always the same thing but I'm open to changing. I am simply looking for the reason sot want to do so. So far, All I have seen as proof is that EVERYONE use to do it and so should we. I say What for? I don't want little rosettes in my solid (intended to be a consistent looking flat area) of color and I don't want the hassle of aligning in register, 3 additional angles.
I am not very experienced at the screen angles of any other process...but I will also say this, even in offset/litho The "Rosette" is not a requirement. You see, you can even print CMYK using stochastic dots. As you know, those have no rosette pattern or any pattern at all. They are frequency modulated and they were also "created by" the Litho/offset industry.
I know I sound like an arrogant Gluteus maximus, but I guess confidence often resembles arrogance. I don't mean to be offensive if I sound that way. I prefer to call it being Passionate about what I do. You all know that. I see it in you as well.
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Sim process is done with opaque inks, the difference in colour with misregistration is going to be greater?
Actually, even the term "Simulated" process signify the use of translucent inks. The regular inks must be modified to
A, go through higher mesh to print thinner dots,
B, go through higher mesh to assist in laying the inks down thinner so as to aid in blending.
The ink manufacturers even sell inks (specifically for) the simulated process printing. You can come close to these by just adding some extender or clear base additive to help thin out these regular inks so that they can do both A and B.
To answer your question, I don't know.
The miss alignment of multiple screen angles plays the same result (in varying degrees) as does a miss registered single line screen (over all). Here or there, you will have a tad bit of white showing in one place or another. Often times, (more so than not), you are talking about weather the white shirt is showing over here at 25 microns or over there at 12 microns or 100 microns on the other side. That can be the same in a rosette pattern as well as a single line pattern. The theory that the single line pattern just puts the dots on top of each and does not show the detail of what a rosette would, does not hold water. You are (intending) to blend these inks/dots. So you really want them to blend over top of each other. Where white is to be, you have no dots, where white is to be just a little bit, you have littler dots and so on. Where the print is to be pastel, you will have very small (highlight dots sized) percentages of CMY and sometimes K with a little white shirt showing (like you would with the rosette pattern).
In addition to all of that, I would also say that it's even BETTER if the dots blend together sooo much that you no longer even see a dot, just a continuous tone like photo quality. You can come close to that using 350 mesh and stochastic.
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[url]http://www.norwb.com/index.php?action=dlattach;topic=13.0;attach=83;image[/url]
Ok. Maybe someone can walk me through this step by step to show me the negative. I am serious when I say I am not seeing the point. I'm sure it's me. I'm slow that way.
Ok. I get that the bottom two are different and are (single line angles). I am assuming that the bottom LEFT side is showing a miss alignment...but something happens to the right. I'm assuming that the bottom left is showing how if you miss register, it shows what Yorkie is calling a strobe. Correct?
If the bottom LEFT side is showing a miss alignment, I even prefer THAT over the top two images but not the right. Of course, if that is Yorkies whole point, then just fix the registration. and you will be back to what I've been saying.
A, A single line screen just looks better.
B, You have less variables when using a single line screen.
In the end, these are all just my personal opinions. Not a proven FACT of course. ;) Use what you will.
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I will add that we use 65 line art for our sim process. At more than 14 inches viewing distance it is hard to discern that there are dots much less a single or four angle set. I also believe at higher line counts mis-registration will be less noticeable.
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I will add that we use 65 line art for our sim process. At more than 14 inches viewing distance it is hard to discern that there are dots much less a single or four angle set.
Thats impressive. :o
I also believe at higher line counts mis-registration will be less noticeable.
I would agree with that. I'd love to see some of your printing some time. Images?
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OK, I have an idea. How about next time I print a simulated left chest (huh, it;s been a while since I've done that . . .) I burn the right chest with a a rosette on the same screen?
Dave, can Wasatch output a piece of film with different angles on it? Get one side to be all 22.5 and the other to be rosette? I'd like it to be on the same film so they are both equally registered. Then we are talking same film, same screen, same stroke, same registration!
pierre
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OK, I have an idea. How about next time I print a simulated left chest (huh, it;s been a while since I've done that . . .) I burn the right chest with a a rosette on the same screen?
Dave, can Wasatch output a piece of film with different angles on it? Get one side to be all 22.5 and the other to be rosette? I'd like it to be on the same film so they are both equally registered. Then we are talking same film, same screen, same stroke, same registration!
pierre
An excellent idea. In addition, It would also then benefit to not only see a comparison side by side of a good registered print...but then also have one that is miss registered to see the worse case scenario...and see how they compare.
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I would agree with that. I'd love to see some of your printing some time. Images?
Here ya' go:
(http://i226.photobucket.com/albums/dd127/orion8377/Tshots026.jpg)
(http://i226.photobucket.com/albums/dd127/orion8377/Tshots032.jpg)
(http://i226.photobucket.com/albums/dd127/orion8377/Tshots031.jpg)
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WOW! Very cool!
Who did the art?
I can see the rosette pattern in the sail. Any chance of getting a closeup of that?
really, really nice!
pierre
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Pierre,
The art and seps were done in house. If it helps you should be able to hold down "control" and click "+" or "-" to zoom in and out of a webpage.
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Let me start by saying, GREAT JOB!!! I'm not sure anything can be done to print that job any finer that what you have printed!!! Now let me get out my loupe and discuss it.
In the area encircled by the sea monster, i think i'm seeing a textile moire? What i see is rows of bands where a halftone dot appears to be missing.
Can you confirm if the bands an optical illusion of the camera, burned into the screen or a textile moire?
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Yorkie, that is from loss of dot in the lower percentages of the white underbase. The cause was probably thread eclipse and not weak film. The screens were imaged with the I-jet. I would guess that they were 3% or lower. The white was on a 230 48 micron thread diameter. We now have some 40 micron diameter in use so hopefully that problem will go away.
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Top Stuff. Looks very good.
Any small banding issue in this print is not that big of a deal. Sure, you want to fix it when you see it but it's not very common in a good shop and this looks like a good shop. You may or may not get that at any time depending. It's just a part of the business when your teetering on the threshold of a thread blocking or not. Some times ya just need to try to hold that 3% and when you do, you have to be right on every time. The thing is, most shops (if not all) are not "right on every time". Therefore, I say it's part of the business.
Gotta work. Bosses calling.
Edited to be more politically correct.
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I'd of not even mentioned that banding issue Yokie pointed out.
What is the point of this thread, except for discussing specific issues like this?
Is this forum to boost blue moon's ego? or is it to improve his printing skill?
I see a moire and asked the simple question of its origins. From what i see, i'd bet that if that screen were printed on paper, the pattern would not be visible. Orion seems to be guessing that it the mesh which caused the moire, which would mean that the pattern will still be present of printed on smooth paper.
The dot looks to be darker than 3%, but then again blue moon said his 5% printed as a 17%, so it could be the dot was supposed to be a 3% and it printed as 13%.
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I had an issue like this the other day. It was the shirt actually causing the problem. I printed it on a large piece of paper and it was clean. Weird stuff sometimes this thing we call screen printing.....lol
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Very nicely executed! That's a purdy shnazzy shirt for a high school band! ;)
And you're right Duke... what's the point if there's no pointing, showing and sharing.
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Yorkie, that is from loss of dot in the lower percentages of the white underbase. The cause was probably thread eclipse and not weak film. The screens were imaged with the I-jet. I would guess that they were 3% or lower. The white was on a 230 48 micron thread diameter. We now have some 40 micron diameter in use so hopefully that problem will go away.
While is a none issue to me...and I know I didn't ask you to post this for a critiquing, but since it was opened up as such, I'm betting that it was mesh distortion. Tensioned mesh that is pulled more towards that bottom right corner. I had seen it befo wit mine own eyes. It seems to bend to the right and down. Thats typical of corner distortion but in this print it seems it's a bit far into the printer area.
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How much you wanna bet?
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For anybody wondering what happened . . . the thread went out on a tangent due to a simple misunderstanding. Dan cleaned it up to bring it back on track.
back to the topic . . .
I use the 40 micron 225 and it will hold some nice detail, but 3% at 55lpi or more, 'doubt it. I can hold the 3% dot from accurip (which turns out to be bigger than 3%) on the 330 smartmesh (at 62 lpi) with lower percentages opening quite a bit, but my understanding is that the 3% is the lower limit of that mesh. So 225 will probably max out at 5 (just my thinking). Going to 45lpi, should do the trick though.
What lpi do you use?
pierre
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How much you wanna bet?
so you think it is fabric moire?
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I use the 40 micron 225 and it will hold some nice detail, but 3% at 55lpi or more, 'doubt it. I can hold the 3% dot from accurip (which turns out to be bigger than 3%) on the 330 smartmesh (at 62 lpi) with lower percentages opening quite a bit, but my understanding is that the 3% is the lower limit of that mesh. So 225 will probably max out at 5 (just my thinking). Going to 45lpi, should do the trick though.
What lpi do you use?
pierre
[/quote]
What lpi do you use?
To who's post are you addressing? Is that Orion's or Yorkie's?
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How much you wanna bet?
I don't need to. It's a none issue to me.
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What lpi do you use?
To who's post are you addressing? Is that Orion's or Yorkie's?
Orion's, but if His RH has some input, would love to hear it.
pierre
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My one question is if the 3% is really what the art called for or just Orion's guess? It looks a lot more than 3% to my eye.
If 3% is accurate, is Orion psychic? or involved? or what?
Anyhow, the big question is of the moire is visible in the screen or only shows its ugly self when printed on a shirt?
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My one question is if the 3% is really what the art called for or just Orion's guess? It looks a lot more than 3% to my eye.
If 3% is accurate, is Orion psychic? or involved? or what?
Anyhow, the big question is of the moire is visible in the screen or only shows its ugly self when printed on a shirt?
Yes, it looks like more than 3%. Most of this is all a guess without holding the actual shirt.
Maybe we can get some shirts sent to you for evaluation. I'd volunteer some shirts!
pierre
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I will add that we use 65 line art for our sim process. At more than 14 inches viewing distance it is hard to discern that there are dots much less a single or four angle set. I also believe at higher line counts mis-registration will be less noticeable.
I think that misregistration will be worse with higher lpi - imagine we have same angle screens and a slight misregistration. The smaller (higher lpi) dots will be completely out of register with the other dots whilst the coarser dots will be partially covered.
btw Wasatch can produce any screen you want on the same film, just RIP before dropping onto the layout. I'll have a look. I can do the different screens in their process colour as well.
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The line count is 65lpi. Went back and had the artist pull up the seps file. The white base in the area Yorkie pointed out is at 7% and the reflex blue is at 44%. I need to go back and find my little chart of dot size in microns at various lpi's. You guys are probably right, moire caused by the substrate. But do you know when I hold the shirt in front of me and look at it, the moire is barely visible.
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The line count is 65lpi. Went back and had the artist pull up the seps file. The white base in the area Yorkie pointed out is at 7% and the reflex blue is at 44%. I need to go back and find my little chart of dot size in microns at various lpi's. You guys are probably right, moire caused by the substrate. But do you know when I hold the shirt in front of me and look at it, the moire is barely visible.
You guys are probably right, moire caused by the substrate.
We will never know now, unless you had kept the original exposed screens to see if it was a screen issue. if it wasn't a a screen issue, then you can look at garment weave interference.
The white base in the area Yorkie pointed out is at 7%
If I remember correctly, you said the base was on a 230. You also mentioned using a 65lpi for that job. So if you used all the same line screen on all mesh as most would do, (holding a 7% dot, in a 65 line screen, on a 230 mesh... is hard to do) wouldn't you say?
Seems to be too high of a line count to hold those dots in that area (on a 230 mesh @ 65lpi). It's about the threshold (teetering on the brink of blockage). Any variance in perfection would send it over the edge of being blocked. Having an DTS I-jet produced a more tighter dot (more accurate) than any of these basic digital film printers (to film) With that said, that means that your dot is probably smaller than most 7%'s from a 65lpi from these digital film printers. Thats going to make it even harder to hold than most are familiar with.
Knowing this info reinforces the idea that the area in question is mesh/halftone related. I'm not saying that it's it for sure, but it sure does make more sense. I will also add here, that 7% dot in a 65lpi is well within the area of something that would do what Yorkie said. Could be garment weave interference. It's within that threshold (as well). I do not believe that mesh weave interference is a result of a 35% tint in a 55 lpi halftone though (as stated in his picture example in earlier post. I'm not knocking his statement. I'm not bashing him I just don't agree.
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I think that misregistration will be worse with higher lpi - imagine we have same angle screens and a slight misregistration. The smaller (higher lpi) dots will be completely out of register with the other dots whilst the coarser dots will be partially covered.
I understand where you are coming from. I think what your really saying is that misregistration will be more visible where it it out with higher lpi. misregistration is misregistration but I guess it's semantic at that point. Going back to my original statement, It's my opinion that it would be equally visually "out" when using a single line screen versus a rosette pattern.
btw Wasatch can produce any screen you want on the same film, just RIP before dropping onto the layout. I'll have a look. I can do the different screens in their process colour as well.
This is VERY COOL. That alone, make me want to get Wasatch. We used to be able to do this in Freehand in the beginning. Different dot shapes, different line screens. It was pretty cool and I made use of it back then.
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We used to be able to do this in Freehand in the beginning. Different dot shapes, different line screens. It was pretty cool and I made use of it back then.
I used to like Freehand, it did things that you wanted that Corel & Adobe don't.
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The major issue with the selection of dot shape has to do with how the midtone (50%) area transitions. Most of this halftone business has it's roots in the math. I know, it freaks everyone out when you use the "M" word, but ultimately, all the things we deal with as screen printers can be reconciled with the math. In the case of dot shape, it is really pretty simple, so here goes.
The maximum dot area is at the 50% dot. This is the point at which the positive dot transitions to a negative dot. By this, we mean that on each side of the 50% tone, the dot area is identical, but one is positive and one is negative. So, a 40% positive dot has the same relative area as a negative 60% dot. 70/30, 80/20 and so on.
Now, the dot shape at the midtone join is very, very important for screen printers because our printing process puts down 6X -20X the amount of ink compared to litho or flexo, which are planographic printing processes (thin film ink deposit.) This is important because this thick layer of ink wants to squish around on the garment, especially if you don't flash.
As the dots connect to the adjacent dots, the geometry of the dot has everything to do with how much of a tonal dot gain increase you will experience at the join. The absolute worst dot is the ROUND dot. As soon as the round dots touch at 50%, they form an acute angle (<90?) and this very narrow angle instantly fills in with ink, on all four sides simultaneously. It is not uncommon, under the very best conditions, to experience 40% dot gain in the midtones on textiles. This is not necessarily bad, because it can be mostly managed. Dot gain is a whole different discussion.
The SQUARE dot is better, but you still have all four corners joining at the same time and now the join is at 90?, so it is harder for the ink to fill in the wider angle, hence less dot gain with a square dot, but still very high.
Now we get to the ELLIPTICAL dot and life becomes much, much better. There are two excellent reasons for the improvement. The first has to do with the ASPECT RATIO of the dot. This means the ratio of the length (x axis) of the dot to the height (Y axis) of the dot. Depending on the Postscript Spot function design, you can control this on an almost infinite basis. The purpose of the ASPECT ratio is two fold.
The first is to have the length of the dot connect in one axis before the other can connect. So, for instance, we can have x axis connect at 40% and the y axis connect at 60%. You are decreasing the amount of dot gain caused by corner joins over a much larger tone range, and at two different tonal values.
Second, and critical, is that the angle formed when the x axis joins is an OBTUSE angle (more than 90?) and this is much, much less likely to fill in due to the ink squishing around. You are decreasing the amount of ink at the point of join so there is less volume to spread or squish together. The openness of this angle is determined by the aspect ratio. If you joined at 30% and 70%, the angle would be much, much more open.
So in this sense, the ideal would be an LINE screen with no dots. This was used for engravings many years ago before the halftone process actually became available. Today, while line screens can be used for special effect, they are not really all that popular.
I hope this sheds some light on the mechanics of how the ink behaves during halftone printing. The shape of the dot is influenced by the frequency (lpi) and the mesh thread as well. Generally coarser halftones >45 lpi and finer S Thread meshes, will allow for successful printing of square and round dots, but regardless, all halftones screen printed will benefit from elliptical dots.
Finally, elliptical, ellipse, diamond, euclidian elliptical, etc are all variation of elliptical dots. The generic family of ellipse is simply dots based on different aspect ratios.
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If you mean Coudray, well yeah he is.
speak of the devil . . . Great to see you here Mark!!!
pierre
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author=drdot link=topic=13.msg1979#msg1979 date=1304472169]
Finally, elliptical, ellipse, diamond, euclidian elliptical, etc are all variation of elliptical dots. The generic family of ellipse is simply dots based on different aspect ratios.
[/quote]
I believe that one the underlying problems is that the ratio isn't "really" changing, just the shape of the dot within the cell. Attached is shape i've created, but have not had the time to test.
This example is a round dot halftone at a 2:1 film ratio. This results is elliptical dots oriented to the horizon (regardless of angle). The horizontal elliptical dots are intended to counteract textile moire.
Rather than a 45 LPI or 55 LPI, the halftone might be 60 LPI in one direction, while 30 LPI in the other, or a 50/25 lpi.
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[I believe that one the underlying problems is that the ratio isn't "really" changing, just the shape of the dot within the cell. Attached is shape i've created, but have not had the time to test.
This example is a round dot halftone at a 2:1 film ratio. This results is elliptical dots oriented to the horizon (regardless of angle). The horizontal elliptical dots are intended to counteract textile moire.
Rather than a 45 LPI or 55 LPI, the halftone might be 60 LPI in one direction, while 30 LPI in the other, or a 50/25 lpi. [/quote]
This is an interesting example. I don't know how you built this example, but here are a few things to consider. The actual LPI represents the individual halftone cell which is then made up of the spots or pixels of the output device at the output resolution.
For simplicity sake, let's assume the halfone line count is 50 lpi and the output resolution is 600 dpi. This means each halftone cell is 1/50". Each halfone dot then contains 600/50 or a grid on grid of 12 spots or for each halftone dot 144 individual spots from the output device. Each tonal step would be 1/144 or .69 of one percent for each gradient division between white and black.
You are correct in describing a different apparent resolution in one direction over the other. The problem comes with all ordered array halftones, typically referred to as AM or amplitude modulated halftones, the size of the actual dot will vary directly with the tonal percentage.
This is why moire is so common in highlight and quarter tones. The dots are much, much smaller than they are at the midtone. In fact, the largest dot area for any lpi, as defined by the perimeter of the dot, is at 50%. Dot area mirrors on either side in positive/negative relationship. So, a 40% positive dot is the same size as a 60% negative dot.
The way the dot builds inside the individual cell is determined by the Postscript Spot Function. The halftone designer will create a matrix that assigns each pixel a threshold value for it to turn on. As an example, a 16 x 16 pixel grid is typical to represent 255 steps from white (all off) to black (all on.) Each of the 255 pixels in that cell has an address that is then mapped to the exact change in tone. When that gray tone value presents, the pixel turns on and the dot builds.
The order and shape of the array is entirely up to the designer and the possibilities are almost limitless. I should point out that it is rare for anyone to work directly in native Postscript. This is the software that drives the RIP. Some RIP software will allow access to the Spot Function, but it is not common.
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Can't wait to chime in but need to put it off for a while. Exciting stuff. I love this kind of gab.
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Some RIP software will allow access to the Spot Function, but it is not common.
You can play with the spot function in the Wasatch RIP, it's in lib\basicspot.ps
Here's an elliptical function:
/Ellipse6040
{ exch dup mul 0.66 mul exch dup mul add 1 exch sub }
You can change the ratio of the axes by varying the 0.66 figure - 60/40 = 0.66, 70/30 = 0.42.
Do a backup before messing with any settings!
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The order and shape of the array is entirely up to the designer and the possibilities are almost limitless. I should point out that it is rare for anyone to work directly in native Postscript. This is the software that drives the RIP. Some RIP software will allow access to the Spot Function, but it is not common.
I would be one of those rare individuals who speaks the postscript language fluently. I first learned postscript in about 1989 when i hacked freehand (1.0) to print to a hacked lasertwriter II ntx to print digitally onto attached removable platter hard disk, then swap the disks platter into a mac II i wrote a program to read the image data from a postscriot formated disk and converted the image files to VSAM onto an IBM 4381 mainframe (all new at the time). Then i spent a decade doing other fun projects involving postscript. Anyone remember "lasertalk"?
As a hobby I also write my one device drivers for ghostscript.
Every RIP allows the access of the spot function, it is the application that limits its availability, except for some special purpose rips like the one epson sells for the large format printers, which replaces halftone dots with dithered dots.
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@Yorkie and anyone else who is deeply interested, Adobe Press has an excellent book on Postscript Halftoning written by Peter Fink way back in 1992 or so. I remember poring over it trying to understand halftone arrays, moire periodicity, super cells, irrational angles, and so on. It is still one of my core reference books on digital imaging along with Ulrich's Digital Halftoning.
Here is info on Fink's Book:
Postscript Screening: Adobe Accurate Screens
explains in detail all the issues and specifically covers Adobe
Accurate Screens -- Adobes' own screening technology. Peter Fink
is an expert on the subject of halftone screens as they relate to
color issues.
Author: Peter Fink
Publisher: Adobe Press, Oct 1992.
ISBN 0-672-48544-3
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The things which interest me, go beyond "accurate screening".
"in"-accurate screening was a byproduct of the limitation of the computers of pre-1992. It has been 19 years since 1992. Computers back in the day were 30 mhz, not dual or quad 3 ghz.
It is my belief, that screen printing on textiles needs its own book.
Please go back and review the not proportional ratio screen i posted. Is that in the book?
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It is my belief, that screen printing on textiles needs its own book.
Please go back and review the not proportional ratio screen i posted. Is that in the book?
I think you're missing the point. Both of the references I cited are foundational material to build your skill set. As an example, the post on moire and "strobe effect" would be enlightening as what you describe is, indeed, a form of moire. The discussion in Fink's book on accurate screens, etc, has more to do with moire issues than on processing speed of the computers. Have you read it?
Your interest in a "not proportional ratio screen" is nothing more than a hybrid screening option. Mike Ware of Waatsch Technologies has developed a wonderful hybrid Stochastic/AM screening model available in their Soft RIP product. It is ideal for screen and flexo printers. It's his approach to dealing with highlight and shadow issues inherent with AM halftones. It is his attempt to solve the same problem you are proposing to solve with your idea.
Postscript offers almost infinite possibilities on how to create a halftone model depending on the printing method, ink characteristics and behavior, and substrate. What you outlined is one possible solution.
Structurally it has some issues, but that also is not the point. Experiment. See what you get. That's how discoveries are made.
Any halftone approach is a balance between visual surface texturing (noise), accurate tone translation, and stable consistency of production. The model you are proposing is still an ordered array model (AM) and any ordered array model will have challenges for screen printers.
For us, the ideal halftone model would be an intelligent mix of FM and AM halftoning based on the rate of change of surface detail over any defined area. What this means is that the algorithm would analyze the image and where the detail was low (eg sky, large areas of flat color) it would place an AM or ordered array dot. Where there is rapidly changing detail (hair, fabric texture, regular patterns like picket fence or screen door mesh) you would get an FM dot of a predetermined dot size.
This approach is processing intensive, but offers the possibilities to balance extremely fine detail with precise tone control. It's a way of losing the visual dot as part of the printed image.
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Have you seen Mike's latest wheeze?
Imagine that you can print from 10-90% quite happily but lose detail after that. Mike has got a trick where the dots are postscript down to 10% and remain at that size so that you can print them. To get a 9% dot he removes some of the dots and progressively to 1%. It doesn't look perfect but it's a really good approximation. It's a sort of stochastic approach to AM dots.
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Have you seen Mike's latest wheeze?
Imagine that you can print from 10-90% quite happily but lose detail after that. Mike has got a trick where the dots are postscript down to 10% and remain at that size so that you can print them. To get a 9% dot he removes some of the dots and progressively to 1%. It doesn't look perfect but it's a really good approximation. It's a sort of stochastic approach to AM dots.
I think my old multi light exposure table used to do this on its own.....lol
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Have you seen Mike's latest wheeze?
Imagine that you can print from 10-90% quite happily but lose detail after that. Mike has got a trick where the dots are postscript down to 10% and remain at that size so that you can print them. To get a 9% dot he removes some of the dots and progressively to 1%. It doesn't look perfect but it's a really good approximation. It's a sort of stochastic approach to AM dots.
That is exactly the sort of thing i was discussing in my latest post.
http://www.norwb.com/index.php?topic=142.msg2263#msg2263
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It is my belief, that screen printing on textiles needs its own book.
Please go back and review the not proportional ratio screen i posted. Is that in the book?
I think you're missing the point. Both of the references I cited are foundational material to build your skill set. As an example, the post on moire and "strobe effect" would be enlightening as what you describe is, indeed, a form of moire. The discussion in Fink's book on accurate screens, etc, has more to do with moire issues than on processing speed of the computers. Have you read it?
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No, i never bought that book. In 1992, i was a member of the adobe developers association. Everything that was anything to the postscript language was documented in the developer mailings, including floppies with containing code.
The term "accurate screens" involves the ability to select a specific angle/frequency, rather than the snap value to the nearest adobe screen angle/frequency. This was 100% computer speed related. The snap values match th memory layout of the ram. 1200 dpi does not divide evenly by 55. Either you divide 1200 by 21 pixels and get 57.14 lpi or 22 pixels and get 54.54 lpi.
Postscript offers almost infinite possibilities on how to create a halftone model depending on the printing method
Postscript 3 only implemented the framework for advanced screening, but left it to the manufacturers to implement in the rip. If i'm wrong, you should be able to reproduce a none proportional screen.
For us, the ideal halftone model would be an intelligent mix of FM and AM halftoning based on the rate of change of surface detail over any defined area.
For me, I just want to print pretty shirts. My pet peeve is moires. Beyond FM and AM is morphing shape of the spot and the shifting the phase of the spots. Processor intensive isn't much of an issue these days. A 60 meg raster files is trivial on todays computers.
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bump!
this is a great post that many of the new members have not seen. I thought it would good to bring it into the spotlight again.
pierre