ColorBalance¶

White-balances an image against a reference color.

ColorBalance[image, col] scales the three cone responses of every pixel so that the color cast col stands for is taken out of the picture. It is the chromaticity of col that is divided away, not col itself, so the picture keeps its brightness and col lands on the neutral gray of its own luminance rather than on white:

$ wo 'Round[100 ImageData[ColorBalance[Image[{{{0., 1., 0.}}}], Green]]]'
{{{86, 86, 86}}}

Balancing against white is therefore the identity:

$ wo 'Round[1000 ImageData[ColorBalance[Image[{{{0.2, 0.4, 0.6}}}], White]]]'
{{{200, 400, 600}}}

Correcting for a green cast pulls the green channel down relative to the other two, so a neutral gray comes back magenta:

$ wo 'Round[100 ImageData[ColorBalance[Image[{{{0.5, 0.5, 0.5}}}], Green]]]'
{{{66, 36, 100}}}

A rule sends the reference somewhere other than white:

$ wo 'Round[10 ImageData[ColorBalance[Image[{{{0., 1., 0.}}}], Green -> Red]]]'
{{{10, 0, 0}}}

A single-channel image has no color channels to rebalance, but the balancing gives it some — it is taken up to RGB first:

$ wo 'Round[100 ImageData[ColorBalance[Image[{{0.3, 0.7}}], Green]]]'
{{{40, 21, 86}, {92, 51, 100}}}

A first argument that is not an image is reported:

$ wo 'ColorBalance[5, Green]'

ColorBalance::imginv: Expecting an image or graphics instead of 5.
ColorBalance[5, RGBColor[0, 1, 0]]