Enhance a scanned PDF
Enhancing a scan is four jobs, not one: flatten the lighting, remove the speckle, re-tone the ink and paper, and firm up the edges. Doing them in the wrong order makes things worse — sharpen first and you amplify the noise you were about to remove.
The pipeline below runs them in the order that works, and it measures your document before deciding how much of each to apply.
Enhance your scan
Starts in Clean Scan mode: strong background correction with moderate darkening.
or drop a PDF here — up to 50 MB and 100 pages
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Advanced settings
The pipeline, step by step
- Render the page at print resolution, so enhancement works on real detail rather than a preview.
- Measure the page: paper level, ink level, tonal range, how much colour is present.
- Estimate the paper level locally across a grid and normalise against it, which removes shadows and grey casts.
- Despeckle: a small median filter applied only to the paper side of the histogram, so specks go and strokes stay.
- Apply the tone curve, mapping measured ink towards black and measured paper towards white.
- Unsharp mask, to restore the edge definition that scanning and JPEG compression softened.
- Recolour, keeping the hue of anything genuinely coloured, then re-encode and write the new PDF.
Why the order matters
Noise removal has to happen before the tone curve, because the curve amplifies whatever it is given — including specks. Sharpening has to happen after the curve, because sharpening first would exaggerate noise that the curve then makes darker still.
Restricting the median filter to light areas is the detail that makes despeckling safe. Applied everywhere, a median filter rounds the corners of small text; applied only where the page is close to paper white, it removes dust without ever touching a stroke.
What this does not do
- No OCR. The output is not searchable unless the input already had a text layer, which is preserved.
- No deskew or crop. Page geometry is left exactly as it was.
- No page reordering, splitting or merging. This tool does one job.
Questions
Will enhancement damage a scan that is already good?
Auto Print Enhance recognises a page that is already solid black on clean white and applies almost nothing. If you force a strong mode on a good page, it will over-process it — that is what the mode selector is for.
My scan has a text layer from OCR. Is it kept?
Yes. The invisible text layer sits alongside the page image and is preserved when the page is re-rendered, so search still works in the enhanced file.
Which mode should I use for a photocopy?
Start with Auto Print Enhance. If the background is still grey, move to Clean Scan. If the text is still too light after that, raise Text Darkness rather than switching to Black & White, which discards mid-tones.
Related
- Clean up a scanned PDFClean scanned PDFs: whiten grey backgrounds, remove speckle and shadows, and even out uneven lighting from scanners and phone cameras.
- Make a scanned PDF darkerMake scanned PDFs darker and easier to read. Corrects faint scans, grey backgrounds and uneven lighting from flatbed scanners and phone cameras.
- PDF contrast enhancerIncrease the contrast of a PDF online. Widen the gap between ink and paper so faint documents become readable and print clearly.