Brightness Contrast Image
FreeAdjust the brightness and contrast of an image in your browser with a live preview, then download the result.
Runs entirely in your browser. Your image is never uploaded anywhere.
Click to choose an image, or drag and drop one here
What this tool does
Adjusts the brightness and contrast of an image with two sliders and a live preview, entirely in your browser, then lets you download the result as a PNG.
How It Works
Brightness is a simple additive offset: the brightness percentage is multiplied by 2.55 and added to every red, green, and blue value. Contrast scales each color value's distance from the middle gray point (128): the contrast percentage maps to a multiplier that is 1 (no change) at 0%, rises linearly up to 4× at +100%, and falls linearly down to 0× (completely flat gray) at -100%, using two straight-line segments that meet exactly at 0% so the transition is smooth. Each final value is calculated as (original − 128) × contrast multiplier + 128 + brightness offset, then clamped to the valid 0-255 range. The alpha (transparency) channel is left untouched.
Problems it solves
- Brightening an underexposed photo or darkening an overexposed one before sharing it.
- Boosting contrast to make a flat, hazy-looking photo pop, or reducing it for a softer, muted look.
- Quickly previewing brightness/contrast changes without opening a full photo editor.
Frequently asked questions
›What is the difference between brightness and contrast?
Brightness shifts every pixel up or down by the same amount, making the whole image uniformly lighter or darker. Contrast instead stretches or compresses pixel values around the middle gray point, making dark areas darker and light areas lighter (or vice versa) without necessarily changing the overall average brightness.
›Why does an extreme negative contrast turn the image into flat gray?
At -100% contrast, every pixel is pulled all the way to the middle gray value (128) regardless of what it started as, since the contrast adjustment scales each pixel's distance from that midpoint down to zero. This is expected, mathematically correct behavior at that extreme, not a bug.
›Why does the image sometimes look "washed out" or "blown out" at high brightness or contrast?
Every pixel channel is capped to the valid 0-255 range. Pushing brightness or contrast too far forces many pixels to hit that ceiling (or floor) and get clipped to pure white or black, which is why very strong adjustments can make large areas of the image lose detail and look flat.
›Does this affect the transparency (alpha channel) of my image?
No. Only the red, green, and blue color channels are adjusted, transparency is left completely untouched, so PNGs with transparent areas keep their transparency after adjusting brightness and contrast.
›Is my photo uploaded anywhere?
No. Everything happens locally in your browser using the HTML canvas API. Your image is never sent to a server, which also means it works offline once the page has loaded.
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