How does the contrast adjustment work?

It scales each colour channel around the mid-grey value of 128 using the standard contrast factor, so positive values push lights and darks apart and negative values bring them together.

What range do the sliders cover?

Both brightness and contrast range from -100 to +100, where 0 leaves the image unchanged. Brightness adds or subtracts light; contrast widens or narrows the tonal spread.

What is the contrast formula?

It uses the standard contrast factor F = (259 × (c + 255)) / (255 × (259 − c)), where c is the contrast value mapped to ±255. Each channel becomes F × (value + brightness − 128) + 128, then is clamped to 0-255.

Does it change brightness and contrast at the same time?

Yes. Both adjustments are applied in a single pass per pixel — brightness is added as an offset and contrast scales the result around the mid-grey value of 128, so you can balance the two together.

Will this reduce image quality?

The maths runs on the full-resolution pixels and exports a lossless PNG, so there is no extra compression. Extreme settings can clip highlights or shadows to pure white or black, which loses detail in those areas.

Is my photo uploaded?

No. All adjustments are computed in your browser via the canvas API, so the image never leaves your device.

Brightness & Contrast Adjuster

Brightness & contrast adjuster

Brighten or darken any photo and fine-tune its contrast with two live sliders. This is a quick way to rescue an underexposed snapshot, flatten a high-contrast scan, or add punch to a dull product photo — all without installing editing software and without your image leaving your device.

How it works

The image is loaded into a <canvas> and every pixel is transformed channel by channel. Both sliders run from −100 to +100. Brightness is mapped to an offset b = (brightness / 100) × 255, and contrast to c = (contrast / 100) × 255. A standard contrast factor is computed:

F = (259 × (c + 255)) / (255 × (259 − c))

Each colour channel then becomes F × (value + b − 128) + 128, clamped to the 0-255 range. Subtracting 128 first means contrast scales around mid-grey, so lights and darks move apart symmetrically.

Example

Setting	Effect
Brightness +40, Contrast 0	Each channel gains 102 (40% of 255) — a noticeably lighter image
Brightness 0, Contrast +50	F ≈ 2.0; darks get darker, lights get lighter for more punch
Brightness −20, Contrast −30	Slightly darker and flatter, useful for harsh scans

The preview updates instantly and everything runs in your browser, so your image is never uploaded.