Online Image Contrast Tool

How contrast is calculated

This global RGB transform is centred on channel value 128, not the image’s average brightness. For strength q, f=259*(q+255)/(255*(259-q)); each channel c becomes f*(c-128)+128, clamped to 0–255 and byte-rounded. The percent label is a strength scale, not a measured percentage increase in image contrast.

Checkable examples

RGB(100,160,240) becomes RGB(94,167,255) at 25, or RGB(116,142,177) at -100. The latter is not uniform grey. Neutral RGB(128,128,128) stays fixed. Alpha is retained.

Originals and limits

Each generation starts from the loaded source; effects do not accumulate. Setting 0 restores its decoded RGB, but does not reproduce the original file bytes. Clipped details cannot be recovered from the processed export alone. Contrast can change apparent brightness; there is no separate brightness control.

Inputs are limited to 25 MiB and 24,000,000 pixels. Browser decoding determines format support, commonly PNG, JPEG, WebP, GIF and BMP. Output is a static PNG; animation, metadata and colour-profile preservation are not guaranteed. This is not sharpening, local contrast, region selection or batch processing. Image processing stays in the browser.