Screen Printing Color Separations: Photoshop, Illustrator, and Corel Tips for Sharper Results

HERE’S AN INTERNET truth: No matter what you read, screen printers still are doing color separations in Photoshop, Adobe Illustrator, and CorelDraw. Maybe down the road you will be able to simply have AI do them, but for today they mostly are being done the “old” way.

I am in the trenches every day doing color seps in Adobe Photoshop for large and small companies. I have a LOT of customers who send me Adobe Illustrator (sometimes Corel) files. Why? Because if the file is complex, has a lot of gradations, has a placed raster file, or just over their pay grade, these can be hard to color separate and reduce the color count.

In fact, even if you have any of the automated seps programs like T-Seps, Separation Studio, Quik Seps, Separo (online) or others, you still must tweak the artwork and the seps.

Here are some quick tips that I use every day that will help you create better separations.

Figure 1

Keep the Edges Sharp

For years most of us recommended 300 dpi as the resolution to us. BUT, if you are doing race car type images with tiny sponsor decals on the car and/or any graphic with small text or elements, you should work at 600 dpi to keep the type readable.

Figure 2

Figure 3

Plus, when you open a vector file from AI or Corel in Photoshop make sure to uncheck Anti-aliased (Figure 1). If you don’t your once sharp edges now will be soft (Figure 2) and, when you separate these and turn the seps into halftones, you will have small halftone dots along the edge of what was once a clean graphic. Figure
3 shows an extreme closeup without Anti-aliased turned on and, even though you see the jaggies, the edges are sharp and not soft.

Figure 4

Choke the Underbase the Easy Way

For most color separations with a white underbase, you must choke (make skinny) the base so it won’t peek out around any top colors. If you open a file from AI or Corel or create the job in Photoshop, you also should keep the background transparent. You will need this anyway if you use any of the automated programs. Having a transparent background makes it a snap to choke back the base for the top colors to fall off onto the shirt (and not show any misregistration).

You simply can use the Magic Wand to have Photoshop select around the image (if there are no interior areas to choke). You then can apply a 10-pixel white stroke from the center to the selection, which will reduce the edge by 5 pixels and/or about 1 point (Figure 4). This method is for a file at 600dpi. If working at 300 dpi then us a 5-pixel stroke from the center.

Figure 5

Choke the Underbase with Interior Transparent Areas

If there are interior areas that are transparent for the shirt to show through, it gets harder if you must select all those areas. This method has a lot more steps and if you are new to Photoshop it might be hard to follow. These steps are from a file that already is separated into individual channels in Photoshop.

Figure 6

1. Make sure the file has a transparent background.
2. Create a new layer and place it below the main image in the Layers Panel.
3. Fill the layer with a color not used in the artwork. Bright green always is good.
4. Select the main image Layer.
5. Open the Channels Panel and select the RGB header.
6. Use the Color Range menu (Select/Color Range) and select the color that you created in Step 3. Save this selection as a channel. It now will be at the bottom of your separations.
7.  You must “load” this channel into your underbase channel. Select the Underbase channel. Hold down the Control Key (PC) or Command Key (Mac) and click on the new “Alpha 1” channel. This will load the “marching ants” into your underbase channel.
8.  As in the earlier “Easy” choke, go to Image/Stroke and select 10 pixels/white/from center. This will choke back any areas of the underbase where there is a selection (marching ants).

See Figure 5 and 6 for help with this. This technique is shown on my YouTube channel at YouTube.com/tbiznetwork in the Computer Graphics playlist.