The framed painting above is my high resolution master file, from where ALL such interpretations begin. Illustration 01 is my oval cropped beginning point for these separations. In Tutorial 004 we converted the master image into grayscale as it was my intention there to reduce it to two values- black and white. In this case I want to capture as much of the color spectrum as possible in a limited palette of six PMS ink colors.

So, cropping the image to an oval is my first step, as I like to avoid rectangles and square shapes on T-Shirts; partly because they are more difficult to line up perfectly on fabric and partly because they give the finished shirt an “iron-on” heat transfer look.

New Year’s “Resolution”

Determining the image’s final printing size and screen printing resolution (dots per inch) is the MOST IMPORTANT step in this entire process. It must be done first. Before we do one more thing in this project ALL of this must be considered and solved right now. Because, everything that happens next hinges on this decision and CAN’T be reversed! This is not lithography where you over build your image resolution and there is some fluidity in output. In screen printing a dot is a dot, and silk screen has fixed limits. Dots rendered too small simply disappear and the subtlety of a design is lost. We must make sure that even the smallest dots do print. (In this solution ALL dots are the same size.)

This process utilizes computer technology to “dither” dots that represent the values from the original, within limitations. In other words, the original picture, in computer terms, has at least 256 colors. We are going to translate this full spectrum down to just six colors, requiring dithered dots, made of six colors, that manufacture the illusion of still being most of the original colors. If you’ll jump ahead in this article and look at Illustration 14, you’ll see a slightly oversized picture of our result. The computer’s PIXELS become our new dots for screen printing. I’ve hand painted hundreds of images using small dots, or pointillism, and I can tell you that this method, once mastered, is a lot faster and just as thorough!

Understanding all of this, as most screen printers do, makes these decisions obvious and expected. From having tested this computer pixel translation to printable dots many times, I’ve learned that 60 dots per inch is about right. I also want to make this image a little less than full chest size to accommodate easy addition of client namedrops. With all of this in mind my final image target is just under 7” x 9” at a dpi of 60. These, then are the parameters of this project. Once you understand these steps you are free to experiment with higher or lower resolutions depending upon your screen burning equipment. I’m just sharing my rationale behind my choices.

Continuous Tone to PMS, or line art:

Photoshop has always included the ability to create indexed images, reducing the palette down to any fixed number of colors. In the earlier days of creating digital pictures this function was relegated primarily to development of multimedia presentations and animation, programs that required a CLUT (color look up table) for each picture displayed. This process is essentially a form of POSTERIZATION, a term well understood by screen printers. Converting an image over to INDEXED from RGB is posterization! The first time a screen printer witnesses this there is a great sigh of discovery. Figuring out how to extract each individual color and registering it as part of a package of separations is quite a different issue, and the purpose of this dissertation. I am sharing how I came to solve this.

Step ONE is shown in Illustration 02. Thanks to the evolution of the internet and even greater need for CLUTs, Photoshop, and other programs, devised a “SAVE for the web” facility, and it is time saving and very useful for our purpose. Here you can see, side by side, the original image and the new INDEXED image. Remember, we have already changed the original’s resolution to 60 dpi. I’ve chosen GIF for output, JPEG would leave it continuous tone. I’ve set the number of colors at 7, because the program will assign the transparent background as one of the colors. I will use the remaining six for printing. Once I’ve achieved all of these objectives I select OK. The new image is SAVED to disk. I now have my posterized master file from which I will extract my separations.

I close the original file and I OPEN the new file. It is now an INDEXED Photoshop file. Illustration 03 shows you the default six color INDEXED palette that accompanies it. My next judgement is to edit the individual colors to increase the fidelity and contrast of the individual colors. Illustration 04 shows this.

The lower half of Illustration 05 shows my edited color palette, the one I’m keeping. These are the actual ink colors needed later to print this design.

The Secrets of Illustration 04:

We need to study this picture for a moment for it contains the keys to our eventual success in getting the separate colors out of the image and registering them later on the press. Understanding this is essential.

First, you will notice that I have installed a series of color bars in the lower portion of the image. These represent the actual six colors being used. These are far enough away from the image to allow them being taped out, or blocked out, during the actual printing production. But they are extremely useful during the proofing and color correction stages. These solid colors are subtle and it is often required to make adjustments in our formulae right on the press before the end result we want occurs. These color bars are a great help.

NEXT, and just as important: I’ve installed some small black squares in each corner of the image. Without these most of what we do is futile. They serve two major purposes.

They are the ONLY way we guarantee that each separated color is exactly the same size as we create them, and they serve as registration marks once we’re on the press. This will become more evident as we move along.

TIP: Before extrapolating each color from the image BE SURE TO ASSIGN THE SAME COLOR TO EACH CORNER SQUARE. It must come with the other pixels and become part of the new sep, in each case. This is our key to uniform color keys and registration.

Illustration 10 shows how to do this. Using the EYEDROPPER tool select whichever color you are about to extract. Then, using the PAINTBUCKET tool, click on each square changing them all to the same color. Now select the MAGIC WAND tool.

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THEN, and here’s the next most important TIP: As it shows in Illustration 05, deselect “anti-aliased.” Without doing this it is impossible to select exactly the individual pixels we want. Also deselect “contiguous.” Now use the MAGIC WAND tool to “select” the currently desired single color from the image.

“Dancing ants” will now move about all of the pixels of one color in the image. From the EDIT menu select COPY. From the FILE menu select NEW. And, HERE’s where our planning comes into play. Photoshop knows the size of the image you have copied to the clipboard and it automatically prepares to create a new window that fits it. THIS is the reason for the small squares in the corners of the master image. By picking them up with EACH separate color we ensure that each and every color separation file is the same size! It’s worth it.

So, into this NEW window we PASTE our color separation pixels. They will be the actual ink color. I suggest that you SAVE this file for archive reference. Now we must convert this picture into a color separation for screen printing. Illustration 06 shows how we select “Preserve Transparency” in Photoshop 5.5. Making sure that our foreground color is black we then type COMMAND-DELETE. This converts all of the dots to black. The last step is to convert this file into a BITMAP at 60 dpi, using the IMAGE menu. To get from an RGB file we must first conert it to grayscale and then to bitmap. The final BITMAP file is our actual color separation. This is the essence of the process explained here.

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Illustrations 07, 08, 09, 11, 12 & 13 show the remaining colors as they appear as color separations for this job. Each one has a color bar and the corner squares, which served to maintain uniform image size and to help with registration on the press. Illustration 14 shows the combination of the total six colors in pixels and as they should print on the substrate. In this technique there are no traps and close registration is mandatory.

Illustration 14 shows you all of the indexed colors as they will print on the screen printing press. The inks will belnd better than this on fabric making the visual impression even better. Once you master this technique you'll think up all sorts of ways to apply it to an assignment.

This tutorial shows you my actual steps for producing this T-Shirt.