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Why plain contrast is not enough

A global brightness or contrast slider treats the whole page identically: push it far enough to rescue a faint signature and the paper's yellow tint darkens with it, while already-dark strokes clip to blobs. This tool uses CLAHE — contrast-limited adaptive histogram equalization — which equalizes luminance in small local tiles instead. Faded ink in a stained corner gets the same lift as ink in a clean corner, and the clip limit stops noise from being amplified into speckles.

After equalization, a per-pixel ink mask separates strokes from paper. Strokes are darkened toward their own hue — blue ink stays blue, black stays black — while the paper is bleached toward white. The result is a purified PDF, not a transparent asset: the page is intact, just readable.

Controls that map to real problems

Each setting answers a specific scan defect.

Made for contracts, journals and archives

Executed contracts photographed in bad light, grandparents' letters, historical ledgers, field notebooks — the common failure is the same: ink that faded faster than the paper aged. Because the pipeline preserves pen-pressure texture instead of thresholding to pure black, signatures keep their character and stay legible rather than turning into uniform blobs.

The output also makes a better input for OCR: run the boosted PDF through OCR PDF and the cleaner separation between ink and paper measurably improves recognition on handwriting-adjacent material like printed forms filled in by hand.

Private by construction

Everything runs on Canvas in your browser. A signed contract or a personal journal never leaves your device — there is no upload, no queue, and no server-side processing.