Not all bad scans look the same. A blurry scan has soft edges — text strokes fade into the background rather than having a sharp boundary. A grainy or noisy scan is different: the text itself might be reasonably sharp, but the background is littered with specks, the paper looks grey instead of white, or there are irregular patches of darker tone across the page.
These are different problems with different causes, and the fix for one doesn't work well for the other.
Why scans come out grainy
Old or dusty scanner glass
Dust and microscopic scratches on the scanner glass scatter light unevenly. The scanner reads this as variation in the paper surface and records it as speckles in the output. It gets worse over time and is especially noticeable on scans with large areas of plain background.
Scanner DPI set too low
Ironically, scanning at a low DPI (100–150 DPI is common on consumer scanners set to "draft") produces a grainy, low-contrast result because the sensor is sampling the page at wide intervals. Each sample has to represent a larger area of paper, and the averaging process creates uneven tones. Scanning at 300 DPI or higher gives each pixel a smaller, more accurate slice of the page.
The document itself
Faxes, photocopies, and very old documents often have genuine texture to their paper — not from the scanner but from the original. Thermal fax paper yellows and develops grain over time. Carbon copies have inherent texture. The scanner faithfully records all of this.
The right fix: cleanup, not sharpening
Sharpening makes edges more defined. That's useful for blurry text, but for a grainy scan it makes things worse — it amplifies the speckles and noise along with the text edges, resulting in a sharper but messier image.
The right fix for noisy or grainy scans is thresholding and contrast normalisation: the image is converted to high-contrast black and white, light background tones (including speckles) are pushed to pure white, and dark tones (text) are pushed to pure black. The result is a clean, binary document that looks like it was printed yesterday.
The Clean Up Scanned Document tool does this. Upload your grainy scan, and the output is a clean black-and-white version with the background noise removed. It works well on faxes, old photocopies, and any scan where the paper texture is the main problem.
Tip
Rule of thumb: if your scan looks speckled, grey, or uneven — use the cleanup tool. If the text strokes themselves look soft or fuzzy — use the sharpen tool. If both problems are present, clean up first, then sharpen.
When the cleanup tool converts to black and white
The output of the cleanup tool is greyscale (or close to it). If your original document had colour elements — a coloured letterhead, highlighted text, stamps — those will be converted to grey tones or lost entirely. For most document archiving and re-submission use cases this is fine — what matters is legibility, not colour accuracy. For documents where colour genuinely matters, a different approach is needed.
Preventing grainy scans at source
- Clean the scanner glass with a lint-free cloth before scanning important documents. A single fingerprint can ruin a scan.
- Set the scanner to 300 DPI minimum, even for drafts. The file is a bit larger but the quality difference is significant.
- For old or delicate documents, scan in colour mode even if the document is black and white — colour scans often capture tonal variation better than greyscale mode and give cleanup software more to work with.