One of the most appealing aspects of illustrating artwork in alpha channels is that you get a great approximation of what the final print will be both on screen and in a printed proof on paper. In many cases, the opacity of screen-printing inks will make the colors on the garment print look identical to your early proofs. As a result, you'll have to worry less about color matching and hue shifts because all of the colors are contained in their own channels and less polluted by other colors.

  Additionally, the nature of spot colors will allow the artwork to retain much more color vibrancy. This is an important benefit when you have a demanding client that is very serious about color matching and needs to see a paper proof that is representative of the final print on the garment.

  The downside to rendering artwork in this manner is you have to carefully avoid overlapping too many spot channels. Too much overlap yields a heavy print. Each method for creating art has its time and place. After you become familiar with this approach, you'll discover which jobs are a perfect fit.

  Creating a strong template

  A strong template is an outline that defines and drives an image. The contour lines that define spatial elements within the artwork are crucial elements. Boring contours create boring art. In this case, your contours serve in a dual role in that they also determine how easily you'll be able to make layer selections for painting.

  Start by setting up your document for easy rendering. Create a new Photoshop document (CMYK, actual size, and 300 dpi), and add some alpha spot-color channels. Click on the New Channel button at the bottom of the channel dialog box a couple of times to create some these painting channels. Save them for use after the template layer is ready.

  Your comfort with illustration and drawing inside Photoshop will dictate the method you use to create the template. The ideal template for channel painting has black lines that have clean edges and connect in the corners to define solid shapes. You can illustrate in pen and ink on paper and scan it into Photoshop, create a clean vector outline in Illustrator or CorelDRAW, or draw directly into the channel layer in Photoshop with the pen tool and a clean, sharp brush setting. Place the final contour drawing into Photoshop in the new document you previously created and size the image appropriately. To create a template from a placed or scanned in black-and-white drawing, you will first flatten the document on a white background. You can copy this flattened layer and paste it into a process-black alpha channel on the document. The template is now ready for painting in channels.

  Painting in alpha spot-color channels

  This is when things become a little weird for artists who are used to working a design in layers. Instead of using layers, the idea here is to create the design using color channels preset with Pantone colors that represent the final opaque inks you'll print onto the shirts. I follow two simple principles to prevent confusion: I work from light to dark (fill with light colors, then define with dark ones), and I take my time when making selections and will often save complex ones as extra throw-away channels that can be quickly reselected.

  For my leprechaun design, I started by double clicking on the first alpha channel to bring up the channel options. I then set this as a spot channel, clicked the color box to bring up the color picker menu, and selected the color libraries button to pull up the Pantone colors. I made this first channel into Pantone 374, a light lime green.

  I started by filling my leprechaun's hat and coat with the lime color. I selected the black channel template and used the magic wand tool to select the areas that would be colored green. This is where careful drawing and template making come in handy. If you've done it right, you'll have confined areas that are outlined by clean lines. They'll be a snap to select using a medium tolerance with the wand tool.

  To slightly overlap my outlines, I expand this selection by 2 pixels (Select>Modify>Expand), reselected my Pantone 374 layer, and fill the area with solid black.

  The next step is to quickly go through the design and fill all appropriate areas with other flat colors created in additional Pantone channels before I move onto rendering with the darker hues. The fun part is going back with the darker Pantone channels and rendering out the dimension in the design using airbrush and paintbrush settings on specific selections. When this is done, I go back to other pieces of the design and render them the same way by placing them into new layers, creating extra template channels, and then painting them into the existing Pantone channels. It's a good idea to save the file in stages (versions 1, 2, 3, etc., just in case you have to go back later to edit parts of it).

  In this design, I had the background shamrock to render and some typography to add in as well. The last painting step involved going in with care and adding deep shadows in the black channel to really create some pop in the final print. 

  Finalizing the channels and underbase for saving to positives

  The step of finalizing the channels can be tedious, but it's the key to creating a great print. The goal is to knock out any significant overlapping of inks that will build up and mush together on press. An easy way to accomplish this is to Ctrl-click on the image in a channel, select all of the white in the channel, invert it (Ctrl-Shift-I), contract the selection by 1-3 pixels (Select>Modify>Contract), and then clear this area from other channels underneath it. Doing so will allow you to quickly remove unnecessary color overlap and keep the design clean.

  You can use a similar method to quickly create an underbase. Select all the color channels containing image elements that you feel need an underbase (hold the Shift key as you Ctrl-click on the channel image to add to a selection), contract the elements by a pixel or two, and then fill all this information into a spot white channel.

  Finally, fill or paint any areas in the white channel that need solid white. You're now finished with the underbase. When you create a shirt channel that shows the color of the garment and place the spot channels in the proper print order, you'll have a great digital reproduction of an opaque screen print.

  Now that the art is fully rendered and made with an underbase, you can save it in DCS 2 format and output the final channels to a printer as separations. If, for some reason, your RIP doesn't support the DCS 2 format, or your printer doesn't have enough memory to handle it, you can go back and simply split the channels on the design and print each one out separately. However, if you do this kind of work routinely, you'll want the ease of outputting a DCS 2 file. For additional clarity, you can also take a design created in this manner and pull it back into Illustrator, add type to the design using Pantone colors, and print out the final with vector type and bitmap rendering.