Topic awaiting preservation: Halftone Schmafftone and color seperations, Is it the printer? (Page 1 of 1)

So, I'm buzzing along and working with someone who has found a way to create vellums on the cheap with the handy dandy off the shelf printer. These are used to expose a blue masking substance spread across a silkscreen for spot color application of plastisol inks on t-shirts.

So... we get a job that has a flame with a halftone blend of yellow on top of a halftone blend of orange. The art we use for the color seperations are in Black and white. The guy we send the file to sends us back the image in three parts;
1) a base color
2) a halftone going from solid to none up
3) a halftone going from solid to none down

We make three screens, one for a solid white base to make the colors "pop", one for the orange, and one for the yellow.

Here's the question:
Is it the printer that produces the little dots of the halftone?
Or, is it the software that tells the printer to do a halftone?

I have access to Corel Draw or Photoshop... Is either one capable of telling a printer how to do halftones? Or, is there a special printer that is needed?

O.o ps... I guess that wasnt "the" question but actually three questions...
DOH!

Anyone got a clue what I am trying to say here? Or have I somehow complicated a simple process?

Thanks for your replies.

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Los Angeles Computer Repair

It occurs both places, but the actual halftone or dither pattern is often a function of the driver.

Printers be it inkjet, laser, or high-end image setters can only place a single element of ink or no ink on their substrates. These elements called cells and combinations of these cells are arranged to produce differing tones using several methods. Amplitude Modulated or the traditional halftones is one such method.

Now non-postscript inkjets and many laser printer don?t allow you to choose the dither method, so you are stuck with the default dithering method, which is most likely some form of Frequency Modulated dither. Where dots are varied in frequency instead of size, unlike a traditional halftone were the size of the dot is varied. A FM dither would not be suitable for screen-printing as the dots must be smaller to produce smooth tonal gradients.

Now if you don?t have control over the printers dither or halftone patter. You could fake it in Photoshop.

Create your artwork in Photoshop using spot channels or even CYMK mode if you?re dealing with photographs. Save it, then go to the channel menu and select split channels, this should split you image into separate images one for each channel in the image. Now you can convert each channel into a bitmap, use halftone as a dither at the desired settings. Then simply print each of the generated halftone images.

Keep in mind each color needs to be at a different angle or the dots will overlap. For the best results use 30 degrees increments, K45, M75, Y90, C105, this will also help prevent a moiré pattern from occurring. When working with 2 spot colors, I would suggest using angles far apart. Typically you start with 75 and 105 degrees. Leaving 45 degrees for any black printer. If you need to use all 4 screen angles reserve 90 degrees for the lightest color as a slight moiré pattern occurs and it?s best if it is in the lightest ink where it?s not noticeable.

As for the output resolution, use around 800-1200ppi; I find it to be adequate for most output devices. But it really depends on your equipment so some testing maybe necessary.

Here is a link on halftones. Tt might prove useful, there is also a ton of great info at this site as well.

http://www.dtp-aus.com/hlftone.htm


There are also plug-ins for photoshop specificly for screen printing, a bit pricy thou.

http://www.fastfilms.com/


More screen printing info also check out: http://www.screenweb.com/

(Edited by jstuartj on 08-29-2004 09:46)

Cool! Thanks for the info!

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Los Angeles Computer Repair