Gradient Map Equalize

The gradient-map-equalize parameter spreads the colors of a gradient-map evenly across the tones that are actually present in the image, instead of across the full black-to-white range. It is a boolean and defaults to false.

By default, a gradient map reads each pixel’s absolute lightness. An image whose tones all sit in the middle of the range therefore only ever reaches the middle of the color list, and the end colors barely appear. With gradient-map-equalize=true, the image’s tonal histogram is flattened first, so every color in the list gets used and the result has more contrast.

This is most noticeable on low-contrast, hazy or evenly lit images, and least noticeable on images that already span the full range.

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