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October 15, 2004
Colorize Black & White Art by Keymixing
A compositing technique called a key mix borrowed from the visual effects industry can turn a black and white alpha channel into 2-color artwork. What's more, it captures the subtleties of antialiasing and grays more easily than does Photoshop's magic wand tool.
The idea is to treat the black and white artwork as a key intended to mix two images of flat colors.
Let's say we wish to turn the black and white artwork into red and yellow artwork.
We take the artwork and multiply it by the color red using the multiply blend mode.
Next we take the negative of the artwork (the photographic inverse) and multiply it by the color yellow.
Finally we take the two intermediate stages and add them using apply image > add (It's not a blend mode. You have to hunt around for it) *** UPDATE: Add is a blend mode. It's been renamed Linear Dodge. See comments below.
I think this technique captures the complexities of rough, antialiased, or gray edges better than does the magic wand tool (or other selection methods.)
Posted by digital artform at October 15, 2004 12:05 AM
Comments
Wonderful site. Needs an author profile page. (Did I miss it?) ;-)
Photoshop doesn't have ADD mode because of a long-standing legal dispute with Quantel.
Adobe finally figured out they could use ADD if they called it something else. So from now on, use LINEAR DODGE; it's ADD by another name.
Posted by: MK at November 24, 2004 08:35 PM
"Linear Dodge" IS "add" by another name; you're right! I never realized that! Thanks for the heads up, and for taking the time this morning to trade additional emails with me this morning on the subject.
--
As far as the site goes; the blog is a WIP and I'm still getting the hang of how to best organize it. In the meantime, here's a bit more about me:
http://home.earthlink.net/~jfrancis
Posted by: Joseph Francis at November 25, 2004 11:19 AM
I had another thought about keymixing that makes it a little faster and a lot more flexible. Try this:
-Open the B/W image in Photoshop
-Add a Levels Adjustment Layer above it.
-In the Levels dialog, double-click on the black eyedropper
(a color picker will appear)
-Pick the color you want for the Black Point
-Click OK to close the picker
-Repeat with the White Point eyedropper
-Now click once on the black eyedropper
-Click on a black pixel in the image
-Repeat with the white eyedropper
It's a little faster, but more importantly, the color choice is editable in the Levels Adjustment Layer. You can also stack adjustment layers and use blend modes for more complex effects.
(P.S. -- I use the colored Black/White points all the time for color-matching photo composites. Try it!)
Posted by: MK at November 26, 2004 11:00 PM
It's very good, but it has, for me, the disadvantage of being very idiosynchratic to "Photoshop only" workflow. It may be my own weakness, but I tend to initially resist idiosynchratic workflows if I'm aware of a generic one.
To be proficient in Photoshop, users should do exactly as you suggest.
What I like about low-level old school workflows is that they are more portable from app to app. You may be mediocre on a wide variety of apps, but at least you can get around.
What I like about your suggestion is that it's a different approach to the Photoshop workflow. The use of potentially vibrant colors in place of "blacks" and "whites" strikes me as unintuitively creative (meaning: "I'm not sure I would have thought of that, and I like it!") and I'll be sure to experiment more with it.
Thanks!
Posted by: Joseph Francis at November 27, 2004 10:02 AM
Actually the method you propes is quite good; I've warmed up to it.
Posted by: Joseph Francis at June 28, 2005 05:06 PM