Channel Operation

Color > Channel Operation

Performs an arithmetic operation on the channels of the opened image. Only applies to color images (i.e. images with multiple channels).

Download a recipe of example channel operations for your color image. An example color image may be downloaded here.

1. Channel Operation

Variables in the operation can be “Auto”, “auto”; “r”, “R”, “red”, or “Red”; “g”, “G”, “green”, or “Green”; “b”, “B”, “blue” or “Blue”; “c1”, “c2”, . . . , “c50”; and “a”, “A”, “alpha”, or “Alpha”. “Auto” eliminates the hue and saturation information while retaining the luminance.

Mathematical operators can be “+”, “-”, “*”, “/”, “^”, “(” and “)”, “[” and “]”, and “~”.

2. Overflow

Specify post-processing to make sure that the results of the mathematical expression fit within the numerical limits of the image format (minimum is 0; maximum is 255 for 8-bit, 65,535 for 16-bit, and 1.0 for floating-point).

• Normalize Top: (default) The maximum pixel value of the expression’s output is normalized to the format’s max value, 0 remains at 0, and numbers below 0 are clipped to 0.
• Normalize Bottom: The minimum pixel value of the expression’s output is normalized to 0, the format’s max value remains at that max value, and numbers above the max value are clipped to the max value.
• Normalize Both: The maximum pixel value of the expression’s output is normalized to the format’s max value, and the minimum pixel value of the expression’s output is normalized to 0.
• Clip: Numbers below 0 are set to 0, and numbers above the max value are set to that max value.

3. Divide by Zero

How to handle pixels which generate divide-by-zero events during evaluation of the mathematical expression:

• White: (default) X / 0 = white, -X / 0 = black, 0 / 0 = black
• Black: X / 0 = black, -X / 0 = white, 0 / 0 = black

Note that divide-by-zero pixels are ignored when calculating any normalization specified by the Overflow option.