Subtract
Purpose: Subtracts a value from each channel of each pixel of the image. Three modes:
- value: Subtracts the value from every channel value of every pixel in the image.
Remember, the internal working image is floating point, 0.0 - 1.0, so meaningful subtractions
are with numbers in that range. But, you can do what you want... :D
- file: Opens the selected image file, and subtracts every corresponding channel value of
every pixel of it from the working image. rawproc will not attempt this operation if the two images
are not the same dimensions.
- camera: Subtracts the value found in the LibrawBlack metadata item from each channel value of each pixel, after converting the LibrawBlack value from integer to floating point scaled to
the range 0.0 - 1.0.

Properties: See tool.subtract.* in Configuration Properties