Unblur an old photo in four steps
- Scan or photograph the print. A flatbed scan at 300–600 dpi gives the most to work with. A phone photo works if it is flat and evenly lit.
- Let it find the dot screen. Printed photos in books and newspapers are made of dots. If a screen is found, its period and angle are shown and it is removed.
- Set the refocus. The defocus kernel is measured on the descreened scan; the strength slider decides how much of it to apply.
- Save at full size. Every step runs again at full size. The receipt names the screen, the kernel and how many dust pixels were held.
What makes an old print look blurred
Two things, usually together. A print in a book, magazine or newspaper is made of tiny dots on a regular screen, and a scanner records the dots as a pattern that reads as grain or moiré. And many old photos were never sharp — the lens, the enlarger or the copy was slightly out of focus. This page treats the two separately, in that order, and leaves damage alone.
| Dot screen | Found as peaks in the spectrum and notched out; other detail passes through. |
|---|---|
| Soft focus | A defocus kernel measured on the descreened scan. |
| Dust and scratches | Held out of the pass so they are not sharpened. |
| Tears, stains, fading | Not repaired here. |
When this will not help
- Torn, stained or faded prints: that is repair, not deblurring, and nothing here paints over damage.
- Faces that were a few dots wide in the print: no face is generated.
- Black-and-white prints stay black and white; there is no colourisation.
Only soft, with no dot pattern? Fix an out-of-focus photo. To check how blurred the scan is first, check the photo.
Questions
What is a halftone dot screen?
Printing presses make greys and colours out of dots on a regular grid. Scanned, the grid appears as a fine pattern or moiré. In the picture's spectrum it shows up as a few sharp peaks in a lattice, which this page finds and removes with a notch filter.
Will it colourise or restore faces?
No. Colourisation and face generation make things up. This page removes the dot pattern, refocuses with a measured kernel, and leaves everything else as it was.
What does the dust hold-out do?
A speck of dust is a single bright or dark pixel among different neighbours. Refocusing would sharpen it into a harder speck, so wherever a pixel stands far from the median of its neighbours, the descreened pixel is kept instead of the refocused one.
Which scan resolution is best?
High enough that the dots are resolved: 300–600 dpi for most prints. At low resolution the screen can turn into moiré that no longer looks like a lattice, and the page may not find it.
When won't this work?
On damage (tears, stains, fading), on prints that were never sharp to begin with beyond a few pixels of blur, and on scans where the dot screen has already been smoothed into mush by the scanner software.
Is the scan uploaded?
No. Everything runs in this browser tab.
Related
- Fix an out-of-focus photoThe defocus spread on a dial, limited to the part that is soft.
- Check if a photo is blurryMeasure blur before you upload: edge width, a heat map and a form checklist.
- Clear a pixelated imageRead block scaling back to its native grid and enlarge it smoothly; mosaic is refused.
- Sharpen an imageFor soft rather than smeared photos: unsharp mask with a halo limiter.
