Image Arithmetic
Add Example - Solid Colors

One thing you can do with add and subtract is to adjust the colors in an image. For example, to add a little red throughout an image, make an image that consists of a solid color with a small red value such as (32,0,0). When you add this to another image, each pixel in that image will have 32 added to the red value without changing the green and blue values. Of course, PSP provides easier ways of doing this.

I'll demonstrate adding and subtracting some red, green and blue from this image. All adds use divisor 1 and bias 0.

Original
Add red (32,0,0)
Add green (0,32,0)
Add blue (0,0,32)
Subtract red (32,0,0)
Subtract green (0,32,0)
Subtract blue (0,0,32)