Image Brightness

Adjust image brightness without blowing out the highlights

Photos taken indoors, against a bright window or late in the day often come out darker than the scene looked. The image brightness tool lifts or lowers the tones of a JPG, PNG, WebP or GIF with one slider, and a live histogram shows exactly where those tones move.

Three formulas are built in. Midtones bends the tone curve with a gamma exponent, so pure black and pure white stay where they are and nothing clips. Multiply scales every channel the way CSS brightness() does. Add shifts every level by the same amount, like the brightness slider in older editors. The work happens on your own device at full resolution, and several photos can be processed together and saved as one ZIP.

How to use the Image Brightness

1. Drop one or more photos on the upload area, click it to choose files, or paste an image with Ctrl+V.
2. Move the Brightness slider, or type an exact value from −100 to +100 in the box beside it. Positive values brighten, negative values darken.
3. Pick a Method: Midtones for photos, Multiply to match CSS brightness(), Add for flat graphics and screenshots.
4. Drag the split line on the preview to compare, and read the histogram: the dashed outline is the original, the coloured areas are the result.
5. Choose a format under Save as and press Download brightened image, or Download all as ZIP if you added several images.

Image Brightness features

The three brightness formulas

Each formula works on the 0–255 value of every red, green and blue channel. The slider value b runs from −100 to +100.

• Midtones (gamma): out = 255 × (in ÷ 255)^γ with γ = 2^(−b ÷ 50). At +50 the exponent is 0.5 (a square root); at −50 it is 2. Because 0^γ = 0 and 1^γ = 1, black and white never move — only the tones between them do.
• Multiply: out = in × (1 + b ÷ 100), the same as the CSS filter brightness(130%) at +30. Shadows barely move in absolute terms, highlights move a lot, and every level above 255 ÷ 1.3 ≈ 196 clips to white.
• Add: out = in + 2.55 × b. Every level shifts by the same amount, so black turns grey at positive values and the picture loses contrast. It suits flat graphics better than photos.

Worked example: +30 on seven grey levels

The table shows each method at +30 (γ = 0.660 for Midtones). Midtones lifts the dark quarter-tones the most and leaves both ends alone. Multiply pushes 192 almost to white and clips 230. Add turns black into a level-77 grey. That is why Midtones is the default for photographs.

Brightness, exposure or contrast?

Use the histogram to decide. If the hump sits towards the left but the tones still span most of the width, the photo is simply dark — brightness is the right fix. If the hump is narrow and sits in the middle, the picture is flat rather than dark, and the contrast tool (or its auto-contrast option) will help more.

If the whole scene was underexposed by the camera, the exposure tool is closer to what a camera does: it multiplies the light itself in linear space by powers of two and then re-encodes it, which brightens highlights faster than shadows.

Tips and common mistakes

• Watch the clipped highlights figure. If it jumps as you brighten, detail in skies and white shirts is being lost — switch to Midtones or lower the value.
• Brightening a dark JPG also brightens its noise and compression blocks. Values between +15 and +40 usually look natural.
• Darkening with Multiply turns white into grey (255 × 0.7 = 179). To darken a washed-out photo but keep white paper white, use Midtones with a negative value.
• Brightness does not fix a colour cast. If a photo looks yellow or blue, try per-channel auto-contrast first, then adjust brightness.
• Edit first and compress last: adjust here, then shrink the file with the image compressor.