Colorize Signed Image

Make an RGB image of a matrix of signed data.

Make an RGB image of a signed matrix, with positive values in red, negative values in blue, and zero values in white or black. An all-gray option is also present.

The image values are scaled to 0..255, and the same scaling factor is applied to both positive and negative values so their magnitudes can be compared.

An optional gamma-correction factor can be applied to the image, useful to
accentuate small values.

In comparison to POLARMAP, this function actually returns a new 8-bpp RGB image with the transformed values. The advantage is that you can save the image to a PNG for use in documents, the disadvantage is that COLORBAR does not do anything.