Scanner Filter (Document Contrast)
Apply a mobile scan app style filter to a photo of a document: high-contrast black and white via adaptive thresholding, or "magic color" for a sharper and more readable color output.
How it works
In black-and-white mode, the image is split into small blocks and a brightness threshold is calculated locally for each block (adaptive thresholding): this keeps text sharp and the background white even if the lighting isn't uniform across the photo. In "magic color" mode, contrast and saturation are simply boosted for a more vivid result, close to the original but more readable.
Why use adaptive thresholding instead of a single threshold?
A photo of a document taken on a phone rarely has perfectly uniform lighting: a single threshold applied to the whole image would create gray areas or darken poorly lit parts that should remain white. Calculating per small blocks adapts locally to these variations.
Which mode should I choose for a document with important colors (diagrams, highlights)?
Choose the "magic color" mode if the document contains colored elements you want to keep (charts, highlights, photos). Black-and-white mode, more contrasted and lighter, is better suited to plain text or a contract to sign.
100% local processing: the filter is applied directly in your browser, your document is never sent to a server.