Adjust Image Brightness and Contrast

Dark phone photos, flat scans and washed-out screenshots usually need the same few corrections: more light, more contrast, brighter midtones, a warmer or cooler tone. This tool applies them with exact, documented maths: brightness, contrast, gamma, exposure in stops, warmth and saturation, plus automatic contrast or levels. Every setting works the same in Chrome, Safari and Firefox, a batch gets identical settings, and the images never leave your device.

How to use this tool

1. Choose one or more images.
2. Optionally pick Auto contrast (keeps colours) or Auto levels (also removes colour casts).
3. Adjust exposure, brightness, contrast and gamma; add warmth or change saturation if needed.
4. Download the result in the original format, or as PNG, JPG or WebP.

Formula

brightness: v + 2.55b; contrast: f(v − 128) + 128 with f = 259(c′ + 255) ÷ (255(259 − c′)), c′ = 2.55c; gamma: 255(v ÷ 255)^(1/γ); exposure: sRGB → linear × 2^EV → sRGB

v is a channel value 0–255, b and c the brightness and contrast settings (−100 to 100). Steps run in this order: auto correction, exposure, brightness, contrast, gamma, warmth (red + 0.3w, blue − 0.3w), then saturation, which moves each channel away from the luma Y = 0.299R + 0.587G + 0.114B by (1 + s ÷ 100). Values are clamped to 0–255 after each step. Auto correction stretches the 0.5th–99.5th percentile range to 0–255.

Example

Take the blue #2563EB (37, 99, 235). Brightness +20 adds 51: (88, 150, 255). Contrast +50 uses f ≈ 2.954, so green 99 becomes 2.954 × (99 − 128) + 128 ≈ 42, while red falls to 0 and blue rises to 255. Gamma 2 lifts the midtones: 255 × √(99 ÷ 255) ≈ 159. +1 EV doubles the light: green 99 becomes about 137.