Ellipse Vrs Dot shape benefit "example attached"

[Dottonedan]

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).



Here you can see that you get about 19-20 dots of transition using (ELLIPSE).

[Command-Z]

I always thought ellipse was used in order to prevent moire.

[DraginInk]

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!

[Printhouse]

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.

[Dottonedan]

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.

[DraginInk]

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    

[squeezee]

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

[Dottonedan]

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.

[yorkie]

I disagree with everything which has been said. 

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.

[Dottonedan]

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.

[squeezee]

Picture of a line screen:
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.

[Dottonedan]

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

[squeezee]

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)

[yorkie]

Here is an example, as best i recall, 55 lpi-25% tint, heavyweight t-shirt, manual press.

[yorkie]

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.