Turn the brightness, contrast and saturation of a photo up or down and watch the result change as you drag. 100% is the picture you dropped; below that the effect is dialled back, above it, pushed. Runs on a canvas in your browser.
The edit is redrawn on a canvas in this tab and re-encoded in the format you dropped — JPEG stays JPEG, PNG stays PNG, and anything else comes back as PNG. Nothing is uploaded.