# Index Separation



## TshirtGuru (Jul 9, 2008)

If I separate artwork at 300 dpi the dots are way to small to burn on a 305 or 200 mesh. So ideally 305 mesh could burn at about 65 lpi. But index "dots" are a lot smaller and won't burn nicely. If I reduce the dpi the dots are larger but then it doesn't look good printed. Is there something I'm missing?


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## TYGERON (Apr 26, 2009)

TshirtGuru said:


> If I reduce the dpi the dots are larger but then it doesn't look good printed. Is there something I'm missing?


So are you saying you actually used a lower dpi and did a print and it didn't look good or are you speculating?

If you do 150 dpi to around 200 dpi maximum, at 100% (you don't resize afterwards) and you use proper mesh and can hold that resolution, you should get a decent print. Of course there are other issues...the actual image, the number of colors you can print, how well you print, inks etc.

And remember the image looks more "grainy" on the computer monitor than the actual print will.


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## PositiveDave (Dec 1, 2008)

TshirtGuru said:


> If I separate artwork at 300 dpi the dots are way to small to burn on a 305 or 200 mesh. So ideally 305 mesh could burn at about 65 lpi. But index "dots" are a lot smaller and won't burn nicely. If I reduce the dpi the dots are larger but then it doesn't look good printed. Is there something I'm missing?


That's pretty much how it works!
With wet-on-wet you should get some mixing.
You need to work out what the lowest %dot you can reliably hold at 65lpi. e.g. An 8% 65lpi dot is equivalent to a 230dpi index print.


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## ShirlandDesign (Nov 29, 2009)

I run 190 dpi on 230's and have no problems with holding detail or moires. if you do you seps at a higher dpi and then re sample to 190 some times you will get better results than building your clut's at 190.


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## TshirtGuru (Jul 9, 2008)

Thanks,

Yes I printed some at 150dpi and the quality isn't there. I'll try 200 dpi. 

I'm also needing to print index or simulated process with dye discharge in a week, and the recommended highest mesh count is 156 or 158. Even if I put an extender in the dye discharge I find that it doesn't penetrate enough through 200 mesh or higher. 

So I suppose I need to use 35 or 45 lpi? How do you guys print with better detail with dye discharge?


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## TYGERON (Apr 26, 2009)

Post some pics of what you printed...


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## red514 (Jul 21, 2009)

for index separations, i do not recommend going higher then 200ppi using 305+ mesh counts. 180ppi is good for mesh counts 280+
if you are using lower then 280s i suggest 160ppi.
any lower then 160ppi and it will look like a pointillist painting, very heavy stippled look (could be cool for certain designs)

i have found that an index 'dot' at 180ppi is ~equal too a 5%halftone dot done at 55lpi


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## red514 (Jul 21, 2009)

TshirtGuru said:


> Thanks,
> 
> Yes I printed some at 150dpi and the quality isn't there. I'll try 200 dpi.
> 
> ...


eeeek that dye discharge job is going to be very stippled.
i'd suggest doing a sample sep and printing out a composite to see if you like how it looks before going ahead with the print.

the key to a good index reproduction is image resolution. the higher the resolution the clearer the image, the lower the resolution the less detail and more stippled it looks.


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## TshirtGuru (Jul 9, 2008)

red514 said:


> for index separations, i do not recommend going higher then 200ppi using 305+ mesh counts. 180ppi is good for mesh counts 280+
> if you are using lower then 280s i suggest 160ppi.
> any lower then 160ppi and it will look like a pointillist painting, very heavy stippled look (could be cool for certain designs)
> 
> i have found that an index 'dot' at 180ppi is ~equal too a 5%halftone dot done at 55lpi


Hey pixelpimp,

How do you calculate ppi with dpi? What would 300 dpi be in ppi? Is there a way to put in ppi in Photoshop or do you go by dpi? Thanks


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## tpitman (Jul 30, 2007)

Not to horn in on the conversation, but dpi and ppi and lpi are 3 different things. DPI actually refers to dots from a printer and has little to do with pixels other than how finely a printer can render them, or render halftone dots, or anything, for that matter. PPI refers to pixels per inch, and that is at the nut of index or diffusion dither files and subsequent prints, and is pretty much just a digital phenomenon. LPI refers to the frequency of halftone dots per inch printed onto a substrate, but a halftone dot doesn't describe the same thing as a printer dpi. Halftone dots as we use them were originally formed on wet litho film in the offset print industry out of clumps of exposed grains of silver in the film emulsion. The dots from a laser or inkjet printer can be likened to the exposed silver in litho film creating the image of the dot. As a matter of fact, in print shops using litho film used film is often recycled to retrieve the silver out of the waste film.


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## red514 (Jul 21, 2009)

well said Tom!

Tom explained it well.
how i found out how large a 180ppi index 'dot' (it's actually a square) is compared to halftones at 55lpi (those are the standards i use for my print shops), i printed out test samples and compared them using a light loop, it's just a ruff estimate, based on my visual observation and exposure tests. The index square was ruffly the same size as the 55lpi halftone dot at 5%

hope this helps


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## tpitman (Jul 30, 2007)

Yup. An index "dot" is actually a printed pixel at the specified resolution. From what I've read, in index or diffused dither prints, your file resolution and your specified diffusion dither figure should be the same before converting the image. An image to be output as a 150 ppi image should be at a resolution of 150 at the print size desired (no scaling up or down after conversion). Oddly, you can easily print a 200 ppi dot, but try and hold a 200 lpi dot in screen mesh (maybe you could at, say, 90%). I've printed the former, never figured the latter would even show up. Actually, high-end offset printers now use 180 - 200 lpi, when 15 years ago or so 150 lpi was the standard for a high end offset job.
Where halftone dots fail at low and high percentages of black in your film is because the dots vary in size, whereas an index "dot" is the same size throughout the image . . . there are just fewer of them in low percentages and more in high percentages, and the transitions in gradients aren't quite as linear in terms of smoothness.


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## mikelmorgan (Nov 1, 2008)

We sep our index at 185 ppi and the image looks terrible on the screen but looks great on the shirt (Using 305 mesh). As far as the discharge we have used a 200 mesh with some luck. A 156 works better but for the detail we have gotten away with a 200 mesh. I'm assuming your using an auto to print. The 200 mesh requires a lot of pressure on the flood bar. It will feel like your going to bust the mesh but it has worked for us. Good luck.


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## red514 (Jul 21, 2009)

tpitman said:


> Yup. An index "dot" is actually a printed pixel at the specified resolution. From what I've read, in index or diffused dither prints, your file resolution and your specified diffusion dither figure should be the same before converting the image. An image to be output as a 150 ppi image should be at a resolution of 150 at the print size desired (no scaling up or down after conversion). Oddly, you can easily print a 200 ppi dot, but try and hold a 200 lpi dot in screen mesh (maybe you could at, say, 90%). I've printed the former, never figured the latter would even show up. Actually, high-end offset printers now use 180 - 200 lpi, when 15 years ago or so 150 lpi was the standard for a high end offset job.
> Where halftone dots fail at low and high percentages of black in your film is because the dots vary in size, whereas an index "dot" is the same size throughout the image . . . there are just fewer of them in low percentages and more in high percentages, and the transitions in gradients aren't quite as linear in terms of smoothness.


well said Tom! maybe i should hire you to write my blog, you're very good at clearly explaining things.

It is very important to note, that you should not resize index seps ever (there's some possibilities of minor scaling but please try to avoid it, it often causes major issues).
Always star working on the sep at the desired print size and resolution. Often when you look at an indexed image on screen it looks very bad, the image is very stippled. To get a good idea of how it will print, convert to RGB mode and zoom out to 50%, this should blend pixels together slightly much as they will on press (always try to print index wet on wet)


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## TshirtGuru (Jul 9, 2008)

Sorry I am just not getting it. I understand the differences between lpi, dpi, and ppi but don't know how to use to when separating index films. If I start off with a 300 DPI image in photoshop, where do I change the lpi and ppi? Or can I? When I split the films in Photoshop, it just indexes everything and asks for DPI and diffusion dither. After that it seps it to it's final rendering. Can someone clarify?


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## tpitman (Jul 30, 2007)

After you're done editing your file, you determine the diffusion dither you want to use, and without scaling your art, change the file to match that dither output. In other words, if you decide you want to do index seps at a diffusion dither of 200, change the resolution of your 300 ppi file to 200 ppi, keeping the physical dimensions of the file (8-1/2 x 11, for example) the same. Then split your colors, and do the bitmap/diffusion dither conversion at 200. The window should show the file size at 200 since that's what you changed it to, and you want your diffusion dither to match.
You may want to save the original edited or editable art file in it's original size and do the downsampling/channel splitting/bitmap/diffusion dither operation on a copy. Once you've converted to a diffusion dithered image, you don't want to scale it up or down.


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