Is my image uploaded to a server?

No. All processing is done entirely in your browser using the HTML5 Canvas API. Your images never leave your device.

What do the brightness and contrast sliders do?

Brightness adds or subtracts a fixed value from every R, G, B channel (range -150 to +150). Contrast scales each channel around the midpoint value of 128 using a multiplier derived from the slider (range 0 to 2×). Values are clamped to 0-255 to avoid overflow.

Why does the preview update automatically?

The tool stores the original pixel data and re-applies the adjustment on every slider change without re-reading the file. This makes updates instant even for large images.

Which image formats are supported?

You can upload JPG, PNG, WebP, and GIF files. You can download the result as PNG (lossless, preserves transparency), JPG, or WebP.

Can I reset to the original image?

Yes. Click the Reset button to return brightness and contrast sliders to 0 and restore the original image in the preview.

Image Brightness Tool

Name: Image Brightness Tool
Availability: InStock
Author: Nham Vu

Upload an image, drag the brightness and contrast sliders to adjust, preview the result live, then download.

Brightness & Contrast

Click or drag image here

JPG, PNG, WebP, GIF

Brightness 0

Darker Brighter

Contrast 0

Less More

Output Format

Before / After Preview

Upload an image to start adjusting

Done!

Summary

Upload an image, drag the brightness and contrast sliders to adjust, preview the result live, then download.

How it works

Upload an image — it is drawn onto an HTML5 Canvas and its original pixel data is cached.
As you move the brightness and contrast sliders, the tool reads every pixel and applies a brightness offset plus a contrast multiplier to the R, G, and B channels, clamping each value to 0-255 (the alpha channel is preserved).
The adjusted pixels render to a live preview canvas instantly on each slider change.
Click download to export the final canvas via toBlob() as PNG, JPG, or WebP.

Use cases

Brighten an underexposed photo taken in low light.
Darken an overexposed image before using it as a background.
Increase contrast on a faded or washed-out scan.
Quickly prepare product photos for consistent presentation.
Adjust a screenshot for better readability in a presentation.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu