Reading
What one tap can fill
The fill copies. It does not imagine. Knowing which of those two things you needed tells you in advance whether the result will be worth keeping.
The method, in one paragraph
Every small square of the disc goes looking for the square of untouched picture nearby that resembles it most. Thousands of those answers overlap, and each pixel takes a weighted average of every square that covers it. Good matches count for more than poor ones, so one excellent answer is not averaged away by a crowd of bad ones.
Nothing in that chain can produce a value that was not already somewhere in the frame. That is the reason the failure mode is worth having: when the search cannot find good matches, the result looks like smeared or repeated texture rather than like a confident invention. You can see that it went wrong.
Where it works
| Surroundings | Result |
|---|---|
| Open sky, plain wall, still water, paper | Clean. Nobody will find the patch. |
| Grass, gravel, sand, foliage, carpet | Good. Random texture reassembles convincingly. |
| Wood grain, fabric weave, fur | Usually fine, if the disc sits along the grain rather than across it. |
| Brickwork, tiling, railings, printed text | Poor. A hard repeating grid does not survive averaging. |
| A face, a sign, a wheel, anything a person names | Bad. The result is a smear and the smear is obvious. |
The check before anything is written
Before the fill runs, the ring of picture immediately outside the disc is compared with the middle of the disc and with the wider band beyond it. When pixels in that ring look more like the thing you tapped than like its surroundings, the thing carries on past the patch, and one disc cannot close it.
The refusal is short and it changes nothing: too big for one tap, that needs a region rather than a spot. Nothing about the photograph moves. It is not a warning you can push past, because a fill that ran anyway would leave you with a smear and a saved file.
Why the disc is not adjustable
The size comes from the long edge of your file, divided by fifty-six, held between fourteen and fifty-six pixels. It is a reasoned guess and it is written down as one.
It is fixed because the first control added here would be the last one. A size that can be dragged wants a shape. A shape wants an edge you can soften. A softened edge wants an opacity. Four controls later this is a region tool with a worse name, and there is already a good region tool that is not this page.