Rendering: Faster, Processor! - Blender Foundations: The Essential Guide to Learning Blender 2.6 - page 351

Figure 12.29 The Image input node, with the previous Alpha Over node.
You might be wondering: What's the point of all of this? Why chop a perfectly good render up into dif-
ferent layers only to put them back together in the compositor? The answer: So you can process the objects
differently. In this scene, we'll make the sun glow. Above the original “Sun” Render Layer, add two more
nodes: Filter > Blur and RGB Curves. Send the sun's original rendered image to the Blur node's input.
Set Blur's X and Y values to around 30—this determines the amount of blur in pixels that is performed
on the image. Send the image result from Blur to the input of the RGB Curves node. Grab the center
point of the curve line and pull it up and to the left, brightening the input image. You can attach the
Viewer node to RGB Curves to see what's going on.
Finally, add a Mix node (Color > Mix). The output of the RGB Curves node becomes the primary input
of this Mix node. For the secondary (upper) input, use the output of the very first Alpha Over node, the
one that combines the sun with the image of space. Figure 12.32 shows the increasingly complex node
tree. This mixes the blurred, brightened image of the sun into the pipeline. As we only want to brighten