Wednesday, August 13, 2008

Eliminating Rich Black from Colored Line Art File

I have recently encountered an issue with "Rich Black" in the printing of color comics on newsprint. This outlines the issue and my resolution.

When I color a comic in Photoshop, I usually scan the original art as line art at a high resolution. Then I convert the image to CMYK, set the line art layer to Multiply, and then do the coloring on other layers. At that point I flatten, save and send the art to the publisher.

The problem with this is that Photoshop automatically makes all the line art into Rich Blacks, which means the line art is duplicated on the C, M and Y channels. What you get is a blacker (rich) black, which causes two problems: one, it creates a high ink saturation, which is not condusive to an absorbent paper like newsprint; and two, if the registration is not perfect (which it rarely is in newspapers), then the line art can become an extremely blurry mess.

I used to send Spooner to American Color with the line art and color as two separate files. However, not all layout artists are familiar with how to handle this, so I've had to work up an alternative method.

This post will document my procedure to solve this issue. It is not as time consuming as it appears, yet I'm certain there must be another method that works better. If you know of one, please share it.

This image shows what the file looks like with the Black channel removed. In other words, this is what the image will look like when it is being printed, right before the black ink is printed on top of it. You can see that all the black line art is duplicated by each color plate, and when each color is printed on top of one another, you already have a pretty dark area where the black ink will go. But if it's not precisely aligned with the black ink, you can imagine how it will break the crispness of the black plate.

The image below shows what the yellow plate (channel) looks like by itself. (It looks gray but this is all actually yellow.) So what we need to do is get rid of the areas where the yellow channel is duplicating the black channel.

This is my procedure:

The art at this point is flattened. I open the Channels palette and hide the C, M and Y channels so that only the black channel is visible, and selected. Use the magic wand tool, with the Anti-alias and Contiguous boxes unchecked. Click any black area and it will select all the black on the screen.

Next I make visible and select the Yellow channel, and hide and deselect the black channel. Only the yellow channel is visible and selected. We still have the magic wand-selected area. In the Edit menu, I select "Cut." Then we are left with the following:

Repeat the procedure with the Magenta and Cyan channels. Once this is completed, if we make all channels visible except the black channel, it should look like this:

So now we're getting somewhere. This file will print only black ink where there are black lines, and we will have no rich blacks. But then I discovered a new issue: The black is not 100% black. You can see in the image below that the black looks weak. So we have one more step.

In the Channels palette, we again hide the C, M and Y channels. Only the black channel is visible and selected. In the Colors palette, we use the sliders to bring C, M and Y down to Zero, and slide K up to 100. Use the Bucket Fill tool, with Anti-alias and Contiguous unchecked, and click on a black area. All the black line art will be "filled" with 100% black. This is almost imperceptible onscreen, but will make a difference in the printed image.

What we end up with should look exactly like what we started out with. Only InDesign or Quark will know the difference:

I saved the image as EPS and sent it to the publisher. The prepress guys said they had to run it through a program called Asura in order to turn it into a PDF, so I am sending a Photoshop PDF this week to see if it'll help them skip that step. I really don't like sending art as PDF since that compresses the image into a JPEG. I don't think JPEGs create good print quality images since it is a lossy compression format, but maybe I'm wrong. I was hoping JPEG2000 would catch on, because it improves the compression and reduces pixel loss, but doesn't look like it will.

If you have had similar issues, maybe you will find some use in this. If you have a better solution, than I would love to hear it. Any questions, feel free to let me know.

P.S. I should point out that this is not a situation where I am doing work for a specific publication, so it is impossible to prepare it in advance under any particular prepress guidelines.


  1. Sounds good. But how about trapping? As you wrote in your post, newspaper presses rarely line up each color plate properly. Would this work?:

    -Keep the line art on a separate layer when you convert to CMYK.
    -Select the black on the line art layer (after you do your magic to make it 100% black) and then go to Select/Modify/Contract... and contract your selection by a couple of pixels.
    -Select your color layer and then cut out the black selection from each channel.
    -Flatten the image. If you zoom in you can see that the black overlaps the color which would give your cartoon some margin of error for registration problems.

    I know Photoshop has an actual "Trap" function but I'm not sure how it works.

  2. I think that's a great idea. That issue has concerned me, and I'll try this next time and see what the results are. Sounds better than trapping.

  3. Hi Ted (and fellow tubbers!). I just saw Stacy's post on the Wisenheimer ...

    I've been working with a series of PDF files lately and learned that you can turn off the JPG compression in Photoshop to maintain image quality.

    But with respect to line art ... I don't know if this will help, but I do the following:

    - scan high res grayscale
    - adjust levels
    - convert to bitmap
    - convert back to grayscale (and then CMYK)
    - use Select -> Color Range menu and pick "Shadows" under the Select drop menu
    - With the solid black line art selected, create a new layer VIA cut (Shift+CTRL+N in Windows)
    - rename and lock line art

    Using this method, the line art layer contains only black -- with transparency. The white portions will remain part of the default "Background" layer.

    Hope this makes sense!

  4. Ted, nice to see someone else wrestling with this and I like reading different approaches. Two things I do that I think are simpler than yours (but may not solve your problems--I haven't tried your way yet, so some details may elude me):

    I begin the same as Mike, converting scanned high-res artwork to Bitmap then back to CMYK so I've got tiny crisp black edges. Then I:

    1. Lasso the entire drawing and Select the C, M and Y channels simultaneously (with shift key), then delete. This clears everything out of those channels and leaves 100% black ready to color.


    2. With the line art colored and flattened, use Select Color to choose rich black (63C/52M/51Y/100K) and Fill with pure black (0/0/0/100). Obviously this would also work if you haven't colored it yet. Since the art's been bitmapped, this catches it all.

    If other layers are involved, I do the same to them, fast and easy.

    When done, I Trap. I like W Rand's idea (is that Wes?), but until now have just used the Photoshop Trap function and like it fine. It automatically adds however many pixels of color you specify to color areas that border black and seems to make the printer happy.

    A good, detailed post, thanks!

  5. Brain and Mike, thanks! I appreciate it. I'll be doing some experimenting with your suggestions.

  6. Maybe I'm missing something here, but typically wouldn't you work your color in Photoshop at about 300 dpi...then submit a separate high-res, monochrome tiff file (1200 dpi) to the printer as your black plate? This would avoid all of the cmyk shuffling described above and provide a nice sharp image for your line art. You would only use a 300 dpi layer of your line art as a guide for coloring and trapping.

    A little late on this discussion I know.