Spot Color Seps: Photoshop Making an Underbase

Due to a few inquiries….Here’s my method creating an underbase white screen in Photoshop CS2-3 for any color screen printing.

That is non screen printing terms, simply creating a base white ink to print on a t-shirt before you print all of the other colors.
Not a vector spot color sep how-to, but the rarer, scarier…Raster/Bitmap Spot Color Sep….oooooh.

Actually it’s not scary at all once you know the process, and result of what you are trying to accomplish.

So creating an Under Base for screen printing, is really just a practice used in screenprinting to create brighter prints on dark garments, some may say it’s not needed except on dark pieces of apparel, but sometimes with certain clients, designs need to be printed on a variety of different color garments, and well, you need the print to look identical on the red, as it does on the green, as it does on the black, and white tees. This is tricky, without the under base white film, so we make it a habit to include this with all of our seps, it’s not hard, and I suppose you can just make an action of it anyways.

And technically the perfect way to make an under base white in my opinion, is to do it last. If all of your other spot colors are perfect, you can simply calculate all of the colors together, minus the black of course, and for best results curve it down 1 notch or 2….

But here is the jist of it, if you’d like to create an easy underbase off an image.

1).Start off with an RBG file

• This is just a sample Backprint Zoom.
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2.) Make sure the Background is Black

3.)Flatten the Image

4.) Open your Channel mixer.

• Check the monochromatic box.
• Output Black: is a mixture of
• Red 100%
• Green 0%
• Blue 42%
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5.) Convert Mode to Greyscale Mode
6.) Curve Adjustment

• Channel: Current Channel
• Curve: point list
• point 26, 0
• point 243, 255
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7.) invert

• Basically you have all of the colors minus the black channel here…and is good to go in most circumstances…but if you look closely at this example there are a few tweaks that would help the print once it gets to press.I think the biggest issue with this image is, I like the Dark Blues to really pop, so I would probably calculate the Blue film into the underbase, and maybe darken up the greys a little, just to keep any bright color garments, like a red shirt, from corrupting the grey ink into a pinking hue…but otherwise I’m pretty satisfied with the result.
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That it…all set….usually I like to calculate the Black channel through to make sure no underbase is mixing with the Black – but usually it shouldn’t…basically it’s just a precaution.

Also alot of times it’s nice to let the colors bleed onto the shirt slightly on the edges, so occasionally I like to go back to the curves adjustment, and use the white eye dropper tool to find and remove any 1 or 2% pixels….it just helps any white sneaking out on the t-shirt.

So I’m sure many will ask if this the best way to do this….well definitley no…but it is a pretty proven way…and you can always be a perfectionist about your films, an sep every element independently, and retweak til your blue in the face…but in the long run, you just gotta decide what’s best for you, and your client….there is always a median between Time, Quality, and Price….and this is just another method in finding that grey area.

Drew