BYTETOOLS

Histogram Equalization Tool

Equalize an image histogram online to rescue flat, hazy or underexposed photos, with an adjustable strength slider and before and after histograms.

Drop a flat or hazy photo to equalizeProcessed locally — never uploaded

What is the Histogram Equalization Tool?

Histogram equalization is the standard fix for a photo whose tones are all bunched together — a hazy landscape, a flat scan, an underexposed X-ray.

  • Classic cumulative-distribution histogram equalization
  • Strength slider that blends the result back toward the original
  • Luminance mode that boosts contrast without shifting hues
  • Optional per-channel equalization for strong colour-cast correction
  • Side-by-side before and after histograms
  • Processed entirely in your browser, exported as a lossless PNG

How to use the Histogram Equalization Tool

  1. 1

    Drop a flat or hazy photo into the upload area.

  2. 2

    Compare the before and after histograms to see how the tones are being redistributed.

  3. 3

    Lower the strength slider from 100% if the full effect looks too aggressive.

  4. 4

    Tick the per-channel option when the image also has a colour cast to remove.

  5. 5

    Click Download PNG to save the equalized image at full resolution.

About the Histogram Equalization Tool

Histogram equalization is the standard fix for a photo whose tones are all bunched together — a hazy landscape, a flat scan, an underexposed X-ray. ByteTools builds the brightness histogram of your image, turns it into a cumulative distribution function and remaps every pixel through it, so tones crowded into a narrow band get spread across the full 0-255 range.

Full equalization can look harsh, so a strength slider blends the result back toward the original — 40% to 60% usually reads as natural. Luminance mode scales red, green and blue by the same factor so hues stay put, while the per-channel option equalizes each channel on its own, which maximises contrast and doubles as a strong colour-cast fix. Before and after histograms sit side by side.

The whole calculation happens on canvas pixel data in your browser, so it is 100% local and nothing is uploaded to a server. Histograms are measured from a downsampled copy for speed, while the Download PNG button applies the same mapping to your image at its original resolution.

Frequently asked questions

What is histogram equalization?

It is a contrast enhancement that redistributes pixel brightness so the tones are spread as evenly as possible across the available range. The image histogram is converted to a cumulative distribution function, and each pixel value is replaced by its position in that distribution.

When should I use histogram equalization instead of levels?

Use equalization when the tones are unevenly clumped rather than simply too narrow, such as hazy landscapes, medical scans or low-light photos. Levels only stretch the endpoints linearly, whereas equalization also redistributes the tones in between.

Why does equalization sometimes look unnatural?

Full equalization forces a nearly flat histogram, which can exaggerate noise and make skies look blotchy. Pulling the strength slider down to somewhere between 40% and 60% blends the mapping back toward the original and usually gives a far more believable result.

What is the difference between luminance and per-channel equalization?

Luminance mode equalizes brightness only and scales red, green and blue by the same factor, so colours keep their relationships. Per-channel mode equalizes each channel independently, which gives maximum contrast but shifts hues, making it useful as an aggressive colour-cast fix.

Is my photo uploaded when it is equalized?

No. The histogram is measured and the mapping applied in your own browser using canvas pixel data. Nothing is transmitted to a server, so private or sensitive images stay entirely on your device.

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