Fixing fisheye photos with Wide Angle Correction
Wide Angle Correction in Paint by Zaweba straightens curved lines in wide and fisheye shots: trace lines, then pick Auto, Fisheye, Perspective or Spherical.
Very wide lenses see a lot, but they bend the world to do it. Doorways curve, horizons bow and the walls of a room seem to bulge. In Paint by Zaweba, Filter > Wide Angle Correction straightens those lines by asking you which lines should be straight and then working out how to make them so.
Why a slider is not always enough
Lens Correction's distortion slider handles mild, even bending across the frame. Strong wide angle and fisheye shots bend more, and differently at different distances from the centre. A single slider that straightens one line can bend another. Wide Angle Correction takes a different approach: you mark real straight lines, and it fits a projection that keeps them straight.
Constraint lines
Start by tracing constraint lines along edges that should be straight in real life. Good candidates are the edge of a building, a door frame, a table top, the line where a wall meets the ceiling, or a distant horizon. Trace them along their whole visible length.
Choose lines spread across the frame, not all in the middle. Lines near the edges carry the most information, because that is where the bending is strongest. A few well chosen lines in different places work better than many lines bunched together.
Choosing a fit
Then choose how the picture is mapped. There are four options.
Auto uses a polynomial fit that adjusts to your lines. It is the one to try first for most wide angle shots.
Fisheye suits photos taken with a fisheye lens, where the frame is strongly curved.
Perspective maps the scene the way an ordinary rectilinear lens would, keeping straight lines straight. It suits architecture and interiors, though the corners can stretch at very wide angles.
Full Spherical, a stereographic mapping, keeps shapes more natural across very wide views, at the cost of some curvature in long straight lines. It suits very wide scenes where people or round objects near the edges would otherwise look stretched.
Try each fit and compare. The right one depends on the scene and what matters most in it.
Correction often leaves the frame an odd shape with empty areas round the edges. Crop to a clean rectangle afterwards with the Crop tool, or fill small gaps. Shooting a little wider than you need gives you room to crop.
Photos that benefit
Interior photos for property listings, where curved walls look wrong. Action camera footage stills, which are usually very wide. Group photos taken close up with a phone's ultra wide lens. Fisheye shots of architecture that you would like to show as straight.
Typical problems
Tracing a line that is not actually straight in reality, such as a curved road, which makes the result bend in strange ways. Using too few lines, or lines all in one area. Choosing Perspective for an extreme fisheye and getting stretched corners; try Full Spherical or Auto instead. Forgetting to crop.
Its neighbours in the app
Lens Correction handles fringes, vignetting and mild distortion, and is often worth running first. Perspective Warp handles planes in a building. The Crop tool's straighten line deals with a level horizon. Each covers a different part of the same job of making the camera's view look natural, and all of them are part of Paint by Zaweba.
