Author Topic: is this moire if so what to do?  (Read 6737 times)

Offline ScreenFoo

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Re: is this moire if so what to do?
« Reply #30 on: January 08, 2013, 02:33:57 PM »
It's right here:
http://murakamiscreen.com/wp-content/uploads/2012/07/HalftoneAnglestopreventmoire.pdf

I can only hope I missed something, but it's amazing to me that it's being implied that a halftone angle change is capable of magically fixing the thread occlusion moire going on here...


Offline Dottonedan

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Re: is this moire if so what to do?
« Reply #31 on: January 08, 2013, 03:24:58 PM »
It's right here:
http://murakamiscreen.com/wp-content/uploads/2012/07/HalftoneAnglestopreventmoire.pdf

I can only hope I missed something, but it's amazing to me that it's being implied that a halftone angle change is capable of magically fixing the thread occlusion moire going on here...



When you say "going on here",  I'm assuming you're referring to Gilly's original issue of the moire.
The screen "angle" comments are 2ndary to his real issue (to me in my opinion) is obvious.


The main issue is the fact he's using 55lpi halftone on low mesh. The "general rule of thumb" as Frog pointed out is all math. Using between 4 and 5, (I prefer 5. will help guide you in a proper mesh to halftone selection.


150 mesh, divided by 4    = 37.5 line screen.

150 mesh, divided by 4.5 = 33    line screen.

150 mesh, divided by 5    = 30    line screen.


At the most, we should be using 38 line screen on a 150 mesh (when you want your fade to go all the way out without interference.


Can you use a higher line screen?  Sure, many do, but many lose those small dots. At best, they get that jagged edge at the end where you see what looks saw toothed. That is the mesh blocking out the last few percentages of dots.  This is so common that it's accepted as par for the course. I might not even fight it that much or re burn a screen at a lower line count in my own shop it's so common (if I saw that). It's not "bad" per say, just not optimum.


Here in Gilly's post, this is an extreme case and is why he's inquiring about it. He knows it aint right. Its a case where you do not want to be and leave your shop (in my opinion). This says to other printers, my shop made an error and let it go.  Thats how I see this stuff (if I say it on a person). I think it says to the average buyer, (something looks wired on that but I can't put my finger on it).


So, with that said, someone might say, "so you would use that big of a dot?"  No. I wouldn't. I would bump up my choice of screen mesh and use a finer dot that matches that. Then adjust how I print it so I still get the needed coverage.


My goal in a gradation (100% to 0%) is to maintain holding all dots as much as possible. Given that I can print most of my jobs on a 230 or higher, I would start there. If I wanted to use 55lpi for sure, it would go like this.


230 mesh, divided by 4     = 57.5 line screen.

230 mesh, divided by 4.5  = 51    line screen.

230 mesh, divided by 5     = 46    line screen.


I would not use anything lower than a 45 line screen on a 230 mesh. 55 is as high as I go and that is pushing it due to the fact that I also want my line screens to be the same on all, and I know I am only using the 230 as my base. Top colors are 300 mesh.


300 mesh, divided by 4     = 75 line screen.

300 mesh, divided by 4.5  = 66    line screen.

300 mesh, divided by 5     = 60    line screen


I would not use anything higher than a 60 line screen on a 300 mesh.


Being that I want all of my art to be the same line screen between a 230 and up, I know I want to use a lpi that will work on my lowest mesh and higher.

So, I round off either lower or higher and I choose 55 lpi on a 230 mesh and use it for my 300's as well.  All of this increases my chances of maintaining as much of the smaller dots as I can.

This applies to S thread as well. The S thread does not jump you another 10 line screens but enables you to pick up another few more dots. You have to consider that you still have so many other variables that effect the dot quality as well such as "screen angle".

Once you know you're using the best choice of mesh (for the halftone used), you can still get moire from other variables such as the emulsion thickness, ink type, screen angles, etc.

22.5 is not (THE) correct one to use for (ALL) shops. Because lets say, your shop is a little more unique are using very thick ink on medium mesh, (thats one contributing factor), than add using a screen mesh that has a very low EOM Emulsion Over Mesh ratio, such as 1:1 of a thin fast pass of emulsion on a medium mesh or the opposite of that would be 2:2 of a very slow pass of emulsion on a medium mesh. Each of these can add to your chances of taking away from or adding to creating mesh opening to dot size/angle interference. Each shop is different but in general 22.5 does work for most.


« Last Edit: January 08, 2013, 03:31:37 PM by Dottonedan »
Artist & high end separator, Owner of The Vinyl Hub, Owner of Dot-Tone-Designs, Past M&R Digital tech installer for I-Image machines. Over 35 yrs in the apparel industry. e-mail art@designsbydottone.com

Offline ScreenFoo

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Re: is this moire if so what to do?
« Reply #32 on: January 08, 2013, 04:12:58 PM »
Seemed like Gilly's initial issue of the moire was addressed with a number of people explaining you can't get a good fade to nothing on a 150 count mesh because of stencil/mesh parameters.

As far as what's going on here, I was surprised to read 'wrong angle' as an answer to the question, I was even more surprised to see people then discussing angle as if it could cause the issue as pictured, but I was by far the most interested in hearing about how Murakami's tech info is listing 'wrong' angle/LPI combos--although for some reason I doubt any proof of how or why is forthcoming. 

I'm with you 100% on minimum dot size--the <5% tones aren't going to resolve on that mesh without the type of moire evidenced in the first photo--no matter what angle you put them at.


Offline Dottonedan

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Re: is this moire if so what to do?
« Reply #33 on: January 08, 2013, 05:04:07 PM »
Seemed like Gilly's initial issue of the moire was addressed with a number of people explaining you can't get a good fade to nothing on a 150 count mesh because of stencil/mesh parameters.



More so, because of the halftones and not the stencil/mesh parameters. It can have nothing to do with the mesh itself, but a combination of the wrong mesh (with that specific halftone) of 55lpi used.




Quote
As far as what's going on here, I was surprised to read 'wrong angle' as an answer to the question, I was even more surprised to see people then discussing angle as if it could cause the issue as pictured, but I was by far the most interested in hearing about how Murakami's tech info is listing 'wrong' angle/LPI combos--although for some reason I doubt any proof of how or why is forthcoming.



I'm not so sure you read it as it is.  It's saying (DO NOT USE THIS MESH) with 22.5 screen angles as THIS MESH does not work well at X angle. In some other areas, it shows that the same screen angle DOES work on a different mesh. The Yellow areas are what NOT to use. The Green area says OK to use.  I think this is a very open tech sheet and very accurate. Not everyone goes this far to say "what angle" works on it and what does not but again, these are just the variables and test results from what (they) learned in there own shop. You may get better or worse results but somewhere close.


 
Quote
I'm with you 100% on minimum dot size--the <5% tones aren't going to resolve on that mesh without the type of moire evidenced in the first photo--no matter what angle you put them at.


True here, in this case with the 55lpi in the equation and no matter the screen angle used.


It's also true, that you CAN use this same 150 S thread mesh at 45 degrees (using the correct line screen that works with it like 30 line screen....and maybe still get moire, but switch it to 22.5 degrees and it's gone.


Just to be clear here, I'm not arguing your position. I am simply pointing out or pin pointing in more detail. Most everyone is right about not using that mesh, but I was explaining what line count should work best on that mesh.

Artist & high end separator, Owner of The Vinyl Hub, Owner of Dot-Tone-Designs, Past M&R Digital tech installer for I-Image machines. Over 35 yrs in the apparel industry. e-mail art@designsbydottone.com

Offline Gilligan

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Re: is this moire if so what to do?
« Reply #34 on: January 08, 2013, 06:38:14 PM »
Just so everyone knows... I'm still here and still reading every bit of it.

I never thought angles was the answer to my problem.  I just wanted to make sure that it was in fact moire and at that point I assumed it was the mesh count.  I did the math before... I still wanted to see what it looked like... it was something for us to play with and see what did what.  I wanted to see some of the best shading I figured I would use and I didn't really care all that much if it didn't go below 20%, I just wanted to see it go.

I actually wanted to do a gray scale photo for my first test, but the wife had this design for some of our own shirts and wanted to see it printed... as we all know, they get what they want. ;)

Offline Chadwick

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Re: is this moire if so what to do?
« Reply #35 on: January 08, 2013, 08:39:30 PM »
Gilligan,

Sometimes it's best to 'just go for it' when experimenting.
I didn't read all the posts above, but you got some good advice.
Have some fun with it.

And it's much easier to get answers, if you know what questions to ask, and all that.
Cheers.
 :)