Graphics Reference
In-Depth Information
Color Changes
Beyond special effects, the compositor can be used to
enhance images with color correction. Color correction
using RGB curves is a complex topic, and entire topics
have been written about it. I'm going to give it to you in
a couple of hundred words.
The RGB Curves node, found in the Color category, is
the primary method for adjusting color in the compositor.
Figure 12.21 shows the node. It takes an image as input,
and delivers one as output. The diagonal line in the middle
of the node's workspace is the default “curve.” LMB
clicking on that line and dragging it adds a control point,
which deforms the line into a curve. You can LMB click
multiple times on the curve, adding more and more control
points as you need them. Also, LMB clicking and dragging
on existing points moves them, altering the shape of the
curve.
Without going into a bunch of color theory, Figure 12.22
shows several common curve configurations, as well as their
result.
Figure 12.21   The RGB Curves  node.
You can also adjust the curves for each of the three color channels (R, G, and B) individually. The CRGB
button set at the top of the node controls which channel is displayed in the workspace, with the “C”
standing for “Combined.” Working with the individual color channels is one way to alter the colors in
your image. For example, raising the center point of the green curve shades the image green.
If you're looking to give subtle (or even not-so-subtle) color casts to your images, though, there is a much
better way.
Color Grading
So far, the compositor has only been used as a straight-through tool to add effects to an image. There is
a single input, which passes to several nodes in turn, and finally to an output. The great strength of the
compositor, though, is its ability to combine different inputs.
Let's go back to the default compositor setup: a Render Layers node and a Composite node. You can
keep working in the same workspace by LMB selecting the intermediate nodes and using the X key to
delete them. To this basic workspace, add a Mix node from the Color section of the Add menu. The
Mix node is shown in Figure 12.23 . Notice that it has two Image input sockets. The Mix node's job is
to accept two images and mix them according to the configuration of the node's controls.
Connect the Render Layers Image output to the upper Image input of the Mix node. Also, send the Mix
node's output to both the Composite node and to a Viewer node so you can see what you're doing.
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