Adjust image contrast — free online tool
Raise or lower contrast from 20 to 180 percent. The formula, a worked example (100 becomes 86 at 150 percent) and where shadows and highlights clip.
The preview will appear here after you select a file.
What to know
Contrast pivots around mid-gray. On a 0 to 1 scale each channel becomes (value - 0.5) x contrast + 0.5, then is clamped to the 0 to 1 range. At 150 percent a pixel of 100 (0.392) becomes (0.392 - 0.5) x 1.5 + 0.5 = 0.338, which is 86, so darker values get darker, and a pixel of 128 stays where it is.
The clipping points are easy to compute. At 150 percent everything below about 43 turns pure black and everything above about 213 turns pure white, so a hazy photo gains punch but loses its deepest shadow detail. At 80 percent the effect runs the other way: black rises to about 26 and white falls to about 230, which gives a flat, faded look that works as a base under text.
Reach for this slider on foggy landscapes, scans of faded prints, and screenshots that look washed out. It pairs naturally with Saturation, because higher contrast makes colors feel more vivid even though no color was added. Moving both by large amounts at once tends to look harsh, so change one, look, then the other.
The range is 20 to 180 percent with 100 as neutral. Exports keep the source format at quality 0.92, and holding the original button compares against the untouched image.
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How to use Adjust image contrast — free online tool
- Add a hazy photo or a faded scan.
- Drag Contrast from 100 to 135 and watch the preview.
- Hold the original button to compare and check that dark areas keep detail.
- Press Apply adjustments and download the result.
Quick answers
What exactly happens to a pixel of 100 at contrast 150?
It becomes 86. The formula is (value - 0.5) x 1.5 + 0.5 on a 0 to 1 scale, so values below mid-gray move down and values above it move up.
Which values turn pure black or white at 150 percent?
Roughly everything under 43 becomes black and everything over 213 becomes white. That detail cannot be recovered in the exported copy.
Why would I lower contrast on purpose?
At 80 percent black becomes about 26 and white about 230, which produces a soft, faded base for text overlays or a quiet background image.
Does contrast change the average brightness?
Not at the mid-gray pivot, but a photo whose average is darker or lighter than mid-gray will look darker or lighter after a large change, so check Brightness afterwards.