Index Separating in Adobe PhotoShop

Index color separation converts a design/image into a diffusion dither random pixel pattern that almost totally keeps you away from the moire pattern problem. A moire pattern is a waveform pattern caused by interference between half-tone dot angle and screen mesh.

The difference between diffusion dither and halftones is that halftones create shading using different size dots and dithering uses the same size dot but spaced out. It looks like stippling. In index printing, the dots do not overlap like in CMYK to create other colors. Instead they are printed beside each other. This helps eliminates the problem of uneven pressure and color shift that can happen in CMYK or simulated process. I also find this a great advantage to those printers who have smaller shops using manual presses.

This process may take a few tries on your part to get the hang of it. I usually give it a go a few times in order to get the best colors selected. This is a judgment call on your part. You will have to focus your eye for color for this.

First determine how many colors you can print. You have to have the ability to print at least 6 colors to use index separations. The more colors you are capable of the better. A 12-color job will look better than a six or 8. More colors allow you more shades of certain inks.

I only recommend index separations for light garment printing. I have seen it done on dark garments and in my opinion, if you are going to print dark garments, use simulated process. I personally think it looks better and more consistent.

Opening the Image

First of all, I used a downloaded image from the internet for this tutorial to make writing it more interesting. In no way am I encouraging the act of downloading copyrighted material and using it as your own.

Step 1: Open the image you need to separate (File > Open).

[Index Separating in Adobe PhotoShop]

Step 2: Make sure the design is in RGB mode (Image > Mode > RGB color).

Step 3: Image resolution: I normally use 175 pixel//inch but you can use as high as 200 (Image > Image Size > set to 175).

Step 4: Make sure the image is Flattened.

Fine-Tuning the Image

Step 1: Go to Image > Adjustments > Selective Color. In the Colors pull down menu select Neutrals. Change the color percentages (Cyan, Magenta, Yellow and Black) from 0% to 5%. Make sure Absolute is checked in the Method area. Click OK.

Step 2: Go to Image > Adjustments > Levels. Make sure the PREVIEW is checked. Click on the black eye dropper. While holding down the Ctrl key, click on the blackest area in the image. Now click on the white eye dropper, and while holding down the Ctrl key, click the lightest or whitest area in the image. Use your judgment; for some images this adjustment is best left alone.

Step 3: Go to Image > Mode > Lab Color. Open your channels. You should see this:

Select the Lightness Channel and turn off the others.

Step 4: Go to Filter > Sharpen  >Unsharp Mask. Set the Amount around 12%, the Radius up to 1 pixels and Threshold to 0. Click OK.


Step 5: Go to Image > Mode and select RGB.

Now we are done adjusting and tweaking the image. On to the separating.

Picking the Colors

Go to Image > Mode > Index. When the menu box comes uncheck Preview. Make sure that in Options > Dither that Diffusion is selected and Preserve Exact Colors is checked. From the Pallete pulldown menu select Custom. A new box will open called Color Table. Click-drag across all the colors. The Color Picker box will open. Select white and click OK. (It may pop up again. Just click OK again.)

Leave the first box white and click on the second box. The Color Picker again pops up. Using the eye dropper select a dominate color from the image (click inside the imagem not in the popup box).

Repeat this selecting the next available box until you have all the colors you need depending on how many print heads your press has (for this example I picked 10). Don't forget black.

When you are done selecting your colors click OK on the Color Table. In the Indexed Color box that shows, make sure Diffusion is selected in Dither pulldown menu, Amount is 100% and Preserve Exact Colors is checked. Click OK on the Index Color box. Your image should look like this:

The image will look grainy and it should.

Creating the Steps

Now the time has come! This is the easiest part of all. Grab a soda, sit down and relax. Here we go.

Step 1: In order to pull up the colors you have chosen, go to Image > Mode > Color Table. Does this look familiar? It should, it's the same table we used to choose the colors.

Step 2: Click on the first color (not the white). The color picker box will pop up. Click the Custom button. This will match your color up to a Pantone Color. Write this number down. In my picture the flesh color was the first color and it matches up to Pantone 714C. Now Click Cancel.

Step 3: Remaining in the Color Table, click-drag over all the colors except the first one. In my case I will click-drag starting with the blue and dragging to the end. The Color Picker window will pop up. Select white on the picker table and click OK. If the Color Picker pops up again simply select white again and click OK. This will let only one color on the Color Table show, which in my case is the flesh color.

Select the color. The Color Picker window will pop up again. This time select black. Click OK to close the Color Picker and click OK to close the Color Table.

Step 4: Go to Select > All

Step 5: Go to Edit> Copy

Step 6: Go to Edit > Step Backwards. Do this twice.

Step 7: Open the Channel menu. At the top of the menu is a double arrow head. Click this and a fly-out menu opens. Select New Spot Channel.

A popup box will open. Name the channel "Shirt Color" and make its Solidity 100%.

Click on the color and a Custom Color menu will open. Click on Picker and select white for the shirt color. Click OK to close the Picker window and click OK to close the Channel window.

Step 8: Go to Edit > Fill. A pop up box will appear. Use black, click OK. (Black becomes the color you selected and colors everything white. Just bear with me.)

Step 9: Open the Channel menu. At the top of the menu is a double arrow head. Click this and a fly-out menu opens. Select New Spot Channel. A pop up box will open. Name the channel. (In my case I call it “Flesh-Pantone 714C.” I will match this up to something I have on the shelf or maybe mix it. I can change the name later if I want.) Make sure Solidity is 100%.

Click on the color and a Custom Color menu will open. Click a color and type in the color you want: Remember the number I told you to write down? Type that in (in my case 714). Click OK to close and OK to close the Channels box.

Step 8: Go to Edit > Paste. Here is what you should have:

Now repeat from Step 1 except choose a different color. In my case, I would choose the blue. Now the first color I started with, the flesh, I would turn that white right along with the others. You are basically, separating each color from the rest and copying and pasting it into a new separate channel.

Printing the Steps

This is the easy part. From the Channels menu: When the eye is visible the channel is on. If the eye is not visible, it is off and won't print. Turn off the RGB channels and the Shirt Color. In the Page Setup, make sure Registration Marks and Labels are check marked. I also check mark Center Crop Marks. Now one benefit to Index Seps is there is no need to worry about setting the angles for the halftones or setting the line count. Remember: Make sure the eye is on the Channels that you want to print.

Burning the Screens

On these separations I recommend 300 mesh on retensionable frames. (New wood frames will work, but be careful of using sloppy screens that have no tension.) I personally like using the yellow dyed mesh. I feel I get better detail from the dyed mesh plus I can tell at a glance which frames are higher mesh counts. If you ever burned screens for a four color process and had the honor of dealing with tiny halftones you will be surprised at how nice these separations burn and rinse out.

I hope you have found this useful. Please email me at to let me know how you made out with it or if you have any questions. If for some reason something is unclear let me know so that I may change it so it is more understandable. 

Happy Printing.