Sharpen old photos: scan first, then sharpen
| Found | What runs | What stays |
|---|---|---|
| A printing screen | Notched out of the spectrum | The photograph under the dots |
| Film grain | A high threshold leaves it alone | Grain and paper texture |
| Scratches, stains | Nothing | The damage, untouched |
Related on this site
- For printed text rather than photographs: make a faint scan legible.
- If the scan is noisy rather than screened: denoise a photo.
- If the picture itself was taken out of focus: fix an out-of-focus photo.
Questions: sharpen old photos
Why does sharpening a scanned magazine photo make it worse?
Because a printed photograph is a lattice of ink dots, and sharpening the lattice turns it into a moiré pattern. This page looks for that lattice in the scan's spectrum, notches it out, and only then sharpens — with a threshold high enough to leave film grain and paper texture alone.
Will it repair scratches, tears or stains?
No. Those are damage, not blur, and repairing them means inventing what was under them. This page sharpens; it leaves damage as it is.
What does 'lines per inch' mean in the readout?
The printing screen's frequency. The page measures the screen's period in pixels and angle in degrees; at a stated scan resolution of 600 dpi a period of 4.5 pixels is about 133 lines per inch, a common screen for magazines.
Can it unblur an old photo that was out of focus when taken?
Only a little, and the defocus route is the better door for that. Old photos are more often soft from the print and the scan than from the lens; the scan preset here is tuned for that case.
