`HistogramTransform`¶

Equalizes an image's histogram.

HistogramTransform[image] replaces each pixel value by its position in the image's cumulative distribution, spreading the values over the whole range — four dark pixels come back as an even ramp:

$ wo 'ImageData[HistogramTransform[Image[{{0., 0.1, 0.2, 0.3}}]]]'
{{0., 0.3333333432674408, 0.6666666865348816, 1.}}

A histogram that is already flat is left alone:

$ wo 'ImageData[HistogramTransform[Image[{{0., 0.25, 0.5, 0.75, 1.}}]]]'
{{0., 0.25, 0.5, 0.75, 1.}}

Each channel of a multichannel image is equalized on its own, so the same value can land differently in different channels:

$ wo 'ImageData[HistogramTransform[Image[{{{0., 0.5, 1.}, {0.5, 1., 0.}}}]]]'
{{{0., 0., 1.}, {1., 1., 0.}}}

A constant channel has nothing to spread out and passes through untouched:

$ wo 'ImageData[HistogramTransform[Image[{{0.4, 0.4}}]]]'
{{0.4000000059604645, 0.4000000059604645}}

A first argument that is not an image is reported:

$ wo 'HistogramTransform[5]'

HistogramTransform::imginv: Expecting an image or graphics instead of 5.
HistogramTransform[5]

HistogramTransform¶

`HistogramTransform`¶