A knockout is an effect where you replace the normally black line in an image with another color. This can be a very handy effect. It can be used to show an object is transparent, glowing or just to give an image a softer feel. If you use it on characters they tend to look more like they were animated, which can sometimes be appropriate. I use it quite a bit for distant background objects to give them a sense of distance and atmospheric perspective.
Knockouts are also an excellent technique for reducing the impact of over-rendered linework when it interferes with the color. Many inkers use a lot of crosshatching and other shading techniques which don't lend themselves easily to color. Knockouts are an excellent way to preserve these lines while reducing their overall visual impact.
Again, this technique works best on an image you've just about finalized.
For this technique, you'll need the lineart layer intact, so do it before you flatten your image.
We're going to completely remove all the white on the lineart layer, leaving only the black lines. We're going to replace it with "clear".
In this example I've got a simple mascot character I want to adjust the line color on. He looks pretty good already, but I
cut [G]). If you get the gradation tool and not the fill bucket, hit shift [G] to alternate to the next tool. In the tool options along the top of your screen, change the mode to "clear". Uncheck the anti-aliasing option and the contiguous option. Now, using the fill bucket, tap in any white area of your image. Your image should look like this:
think we can make him a little cuter. The first step is to isolate replace all the white area with clear. Highlight the lineart channel to edit it. Now, from the tool menu, select the Fill tool (keyboard short
All the white in your lineart layer should be gone! The checkerboard pattern behind the lineart is Photoshop's way of telling you it's clear and there are no other layers visible beneath it. Change your lineart layer's blending mode back to normal instead of multiply. Check the eyeball on the background layer too, so you can see your entire image again. Your layers palette should look similar to this:
We just want to edit the lines, not the "clear" areas. We can do this by locking the transparent pixels on the lineart layer.
Now, any alterations you make to the layer will not affect transparent areas. At this point, you can simply select a brush (I prefer a hard edged pencil tool) and simply color over the lines. The brush will only apply color to the black lines! Transparent areas are left untouched, as well as all your coloring on the layer below!
You can also use the lasso tool to select areas you want to be the same color and use Fill to color the linework.
In the above image I selected areas of the linework that were black along with large portions of surrounding areas and then applied a Fill. Note that only the area where there were black lines did the color actually stick -all clear areas resisted the Fill. Using the same technique, I soften the body colors a bit.
Almost all the linework on the monkey has been replaced with color holds now! A few more airbrush highlights on the cheek and I'm done!
At this point you could move on to additional effects work. If you're done you can complete the image by flattening the layers.
If at any time you want to restore all the black lines, choose black from the color picker, select all [ctrl A] and simply do a Fill. All the lines will revert to black.
Knockouts are useful in many situations. The can be used to make Glass Objects read a little clearer. They can also be used
for motion type lines, to help indicate something is moving.
Or they can be used for metal objects to help indicate a different texture. The possibilities are virtually endless, so experiment!
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