Apr 27 2009
Adobe Photoshop Tip– Use DCS2 to make the most of a 2 color job
This tutorial originally appeared under the name “Selective Duotone” in DCS2 on MacMerc a couple of years ago and was lost in the shuffle when we converted the site to phpNuke a while back. Well, it’s back in its entirety complete with Photoshop 5.5 screenshots! Here we go…
Check out these three images. The one on the left is the original four color (CMYK) file. The one in the middle is a standard duotone. That being an image that maps two ink colors across the entire ramp of a grayscale image. 
Thus any part of the grayscale image that is 43% grey is always the same mix of the two spot colors. This is not so with the image on the right which is what I call a selective duotone. This image still uses the same two spot colors as the middle image, but care has been taken to emulate the four color image somewhat. Both kinds of duotone have there place and, in fact, the standard duotone is more acceptable in most circumstances. But, nonetheless, you may find yourself in a situation where a selective duotone is called for. There are Photoshop products on the market that do this very effect but, hey, if you can learn this technique, you won’t need ‘em? And once you wrap your mind around the concept presented here, you will be able to apply this to jobs with three or more spot colors – something the plug-ins will not handle.
Step 1: Strategy
In most cases, the job you are working on will already have the colors specified by the designer or client. In this case, I was given a blue (PANTONE 662) and an orange (PANTONE 716) with which to work. It is ideal to work with colors that are already dominant in the original image while also attempting to choose colors that are not too close to each other on the color wheel. By using colors on opposite ends of the color wheel, you ensure that there will be one color to handle cool tones and another to handle warmer tones. These two colors I’ve been given fit that bill perfectly, so I’m set.
Now, looking at the CMYK break down, (you must be using an image in CMYK mode for the purposes of this tutorial. If your image is not in CMYK mode, convert it.) I’m going to use the Cyan channel to represent the cool spot color and the Magenta channel to represent the warm one – you’ll see what I mean in a minute.
Step 2: Fill in the Blacks
Often when images are scanned the Cyan, Magenta and Yellow channels are lightened where the Black channel is at its darkest. This is to prevent problems at the press but it will cause problems with our effect if we don’t account for it. Go to the Image menu, scroll down to “Adjust” and then over to “Selective Color…” and release. In Selective Color, click the bar at the top that reads “Reds” and scroll down to “Blacks.” At the bottom of the window make sure the button beside the word “Absolute” is checked. Now slide all the sliders except the Black to the right all the way. Then click “Okay.”
Step 3: Operating the Channels
In the Channels palette, drag the Cyan channel to the “create new channel” icon. Double-click the name of the new channel you’ve created (Alpha 1, probably), click the “Spot Color” radio button, set the Solidity to 0% and click the Color box. This will call up the Color Picker. If you are using a mixed ink of your own concoction (not a PANTONE color), you can enter the values here (NOTE: you will also have to give your color a name at the top of the Spot Channel Options window). If you are using a color matching system like PANTONE, click the “Custom” button and, in the “Custom Colors” window, select your spot color. At this point, click “Okay” on the Color Picker and “Okay” on the Spot Channel Options window.
Once you’ve done all this, do it again by copying the Magenta channel to a new layer and setting all of this new channels options the same way you did on the first one. Only this time make sure to choose the other spot color from the Color Picker.
Notice how Photoshop has been programmed to automatically enter the name of spot colors from color matching systems. Very nice.
Step 4: Accenting
After both your spot colors have had channels made for them you will have to decide which is the stronger color. This is the one that will handle the image information that the Black channel would have taken care of. In my case the blue is darker and deeper than the orange, so it is the stronger of the two. I take the stronger color and I select its channel by clicking on its name once. I call up the Levels adjustment (Command-L) and set the Black arrow of the Output Levels to 64. Keeping the stronger color channel selected, I Command-click the Black channel. This selects everything on the Black channel that is white …but I don’t want that. I want to select what is black. So now hit Command-Shift-I to invert the selection. Hopefully you are still looking at the stronger color channel. Under the Edit menu select “Fill…” and set it to “Black” , “100%”, and “Multiply” then click “Okay.” Hit Command-D to deselect.
Now the weaker channel gets accented. Select the weaker channel by clicking on its name once. Now we’re going to do things a little differently than we did with the other channel – we are not going to adjust this channel in Levels. Command-click the Yellow channel and invert the selection. Under the Edit menu select “Fill…” and set it to “50% Gray” , “100%”, and “Multiply” then click “Okay.” Hit Command-D to deselect.
Step 5: Cleaning up
You have now essentially finished your duotone …although it might no look like it. Just to satisfy your curiosity, lets see what it looks like! But first, save your file as a Photoshop document.
Now drag the Cyan channel to the trash can icon at the bottom of the Channels palette. No really, it’s okay, you just saved. If it doesn’t look right you can choose Revert under the File menu. Now drag the Magenta, Yellow and Black channels to the trash too. All you should be left with is two channels. If you don’t seem to see your image as a duotone, hold the Shift key down and click on any channel that might not be selected.
Now, how’s that? If the image looks good to you, go to the File menu and choose “Save as…” Name your file however you like but make sure you choose “Photoshop DCS2.0” as your file type. Next you will be faced with more options on how to save this image. My recommendations are to choose “Macintosh 8 bits/pixel”, “Single File with Color Composite (72 pixels/inch)” and “Binary”. Leave everything else unchecked and click “Okay.”
Step 6: Conclusion
Once you get the hang of this you will come to realize that sometimes the Cyan and Magenta channels are not the best ones to start with. If your image didn’t turn out right, that might be the case and you might experiment using the yellow or black in place of one of the other channels. Feel free to experiment. Save copies. Relax.
Step 7: One Word of Warning
Some image setters have a problem dealing with DCS2 files. Before you set all the images in your job to DCS2, talk to the person in charge of getting the job color separated and let them know that you will be using DCS2 files. They may be able to avert disaster by making arrangements to separate your job another way. They may just tell you that you can’t use them but then again they have no problem with DCS2 at all. Nevertheless, you should let everyone know before you go too far.