> For the complete documentation index, see [llms.txt](https://astra-image.gitbook.io/astra-image-6.0/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://astra-image.gitbook.io/astra-image-6.0/processing-tools/histogram-equalization.md).

# Histogram Equalization

Histogram equalization increases the global contrast of an image, especially when the majority of histogram bins are in a small range. After performing histogram equalization, the image intensities are more evenly distributed throughout the histogram. This can be very helpful, especially with under- or over-exposed images.

<div align="left"><figure><img src="/files/w8IEWqpTJOmBeDJkgnuI" alt="The Histogram Equalization tool."><figcaption><p>The Histogram Equalization tool.</p></figcaption></figure></div>

**Equalize RGB channels**\
This performs histogram equalization on each red, green and blue channel individually. In some cases, this can lead to an unwanted color shift.

**Equalize Luminance channel**\
After converting the image to the HSL color space, histogram equalization is done on the luminance channel (L) only. Then the image is converted back to RGB.

**Equalize Value channel**\
This converts the image to HSV color space, then does histogram equalization on the value channel (V) only. The image is then converted back to RGB.