Image Auto Levels
Stretch an image histogram to use the full tonal range, with per-channel and luminance modes, clipping control and a histogram comparison before and after.
Last reviewed by the Radiatus Cloud team
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Most flat photographs are not using the range available
An underexposed or hazy image has its histogram bunched into part of the range, with nothing near pure black or pure white. Stretching that used range to fill the whole scale restores contrast without inventing anything: the tones that were there are simply spread further apart. This is what an auto levels or auto contrast command does, and on a genuinely flat image it is the single most effective correction available.
Clipping a small percentage is what makes it work
Taking the absolute darkest and lightest pixels as the endpoints usually achieves nothing, because a single stray pixel at each extreme means the range is already full. Clipping a small percentage at each end, commonly around half a percent, ignores those outliers and stretches the range that actually contains the image. Too much clipping crushes real shadow and highlight detail into flat black and white, which cannot be recovered.
Per channel corrects colour casts, and sometimes creates them
Stretching each of red, green and blue independently removes a colour cast, because a cast means one channel occupies a different range from the others and equalising them cancels it. On an image that is genuinely dominated by one colour, a sunset or a forest, the same operation destroys the intended balance. Luminance mode stretches contrast while leaving the colour relationships alone, which is the safer default.
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Frequently Asked Questions
What does auto levels actually do?
It finds the darkest and lightest tones actually used and stretches them to fill the full range. Nothing is invented: the existing tones are spread further apart, which restores contrast to a flat image.
Why clip a percentage at each end?
Because a single stray bright or dark pixel makes the range appear full when it is not. Clipping about half a percent ignores those outliers and stretches the range containing the actual image.
Should I stretch each channel separately?
Only when correcting a colour cast, which is what per-channel stretching removes. On an image legitimately dominated by one colour, such as a sunset, it destroys the intended balance. Luminance mode is the safer default.
Can this recover a blown-out sky?
No. Areas already at pure white contain no information to recover, and stretching cannot invent detail that was never captured. Auto levels helps images that are flat, not ones that are clipped.
Why does my image look noisy afterwards?
Because stretching amplifies everything in the used range, including the noise. An underexposed image has proportionally more noise in its shadows, and brightening it makes that noise visible along with the detail.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Upload a flat or washed-out image to stretch its tonal range automatically.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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ImageGenerate favicons and app icons at every required size from one source image, with the exact HTML to reference them.
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