Calculator
What the Brightness Contrast Adjuster does
Brightness Contrast Adjuster: brightness adds a constant to every channel, contrast stretches values away from mid-grey with the standard 259-factor curve, and saturation scales each pixel's distance from its own luminance. Everything runs in your browser and the file is never uploaded.
Pick a file and the Brightness Contrast Adjuster calculates it right here in the page. The work happens inside your browser tab, so there is no upload to wait for and no queue.
Getting the dimensions right before upload avoids a lot of downstream cropping. The Brightness Contrast Adjuster exists to take that particular chore off your hands.
Your picture never leaves the tab, which also means there is no upload to wait for.
The field table, the method and a worked example are documented after the tool for anyone who wants to check the working.
What do the Brightness Contrast Adjuster fields mean?
The Brightness Contrast Adjuster uses 6 inputs. It opens with a complete example loaded, which is usually the quickest way to understand what a field means.
| Field | What to enter | Default |
|---|---|---|
| Image file | stays on your device | none |
| Brightness | accepts -100 to 100 | 0 |
| Contrast | accepts -100 to 100 | 0 |
| Saturation | accepts -100 to 100 | 0 |
| Export as | choose from PNG, JPEG or WebP | JPEG |
| Quality % | accepts 10 to 100 | 92 |
How does the Brightness Contrast Adjuster work?
L1 and L2 are the relative luminances of the lighter and darker colour. WCAG AA needs 4.5:1 for body text, AAA needs 7:1.
Validation runs before the calculation, which is why a mistyped value shows an error rather than a plausible-looking result.
What a typical run looks like
You provide: Image file, Brightness, Contrast, Saturation, Export as and Quality %
What happens: the file is read into memory by your browser, processed locally, and offered back as a download. It is never uploaded.
You get back: a new file plus a brief account of what happened to it, shown in the panel.
How long this takes is a property of your computer, not of our infrastructure, and file size is bounded by browser memory.
How to use it
- Choose your file under Image file, or drag it onto the drop area.
- Put Brightness (-100 to 100).
- Key in Contrast (-100 to 100).
- Fill in Saturation (-100 to 100).
- Pick a value for Export as: the options are PNG, JPEG or WebP.
- Enter Quality % (10 to 100).
- Press Adjust.
- Check Status on the right.
- To keep the result, either copy the link or print the page. Both preserve what is on screen.
What this tool does not do
- Re-encoding a lossy format such as JPEG always loses some detail, even at maximum quality.
- EXIF metadata may be dropped during processing, which is usually desirable but is worth knowing.
- Comparisons across tools can differ where each uses a slightly different definition.
- The tool trusts your numbers completely, so a mis-keyed digit propagates straight through.
- Large files are limited by your available memory, not by an upload quota.
Frequently asked questions
Image file, Brightness, Contrast, Saturation, Export as and Quality %. That is the whole form. Defaults are loaded for all of them, so the form is usable immediately, without filling anything in first.
Brightness accepts -100 to 100. Go outside it and you get an error against that specific field instead of a misleading number.
No. The file is read by your browser and processed inside the page. It is never sent to us, which is also why it keeps working offline once loaded.
It is free with no conditions: no sign-up, and no limit on how often you use it.
It follows the standard definition for this operation, so the result matches what a reference implementation would give.