Why do smartphone wide-angle photos make objects near the edges look stretched, and why isn’t that automatically “fixed”?
Asked 12/17/2015
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Smartphone photos often make faces or round objects near the edges of the frame look stretched or oval. For example, a ball near the corner of a wide-angle phone photo may no longer look circular.
Why doesn’t the camera automatically correct this in software? Since phone lenses and sensors are fixed, it seems like distortion correction could be built into the camera pipeline. Is this a lens distortion problem such as pincushion/barrel distortion, or is something else happening with very wide rectilinear smartphone lenses?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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This type of distortion in the corners is one of the trade offs for having a rectilinear lens that can render a wide field of view that covers a spherical area into a flat rectangular image. If you want things near the edges of such a wide field of view to appear undistorted, then you need a fisheye lens. But the fisheye lens will not produce a rectangular image, it will produce a spherical one. And all of the straight lines in the field of view will appear curved unless they pass directly through the center.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
10y ago
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What you’re seeing is mostly not pincushion distortion. It’s mainly normal perspective/projection behavior from a wide rectilinear lens.
Rectilinear lenses are designed to keep straight lines straight. The trade-off is that objects near the edges of a very wide field of view get stretched, and round objects can appear oval unless they’re centered. A sphere photographed off-center projects to an ellipse even with an ideal, “perfect” lens.
So there often isn’t a simple automatic fix, because “correcting” that edge stretching means changing the projection. If you remap the image to make edge subjects look more natural, you usually introduce other compromises, such as curved straight lines (more fisheye-like rendering) or cropping away part of the frame.
Software can correct true lens distortion such as barrel or pincushion distortion, and many phones already do some of that. But the odd look of people or balls near the edges of wide phone photos is largely a fundamental consequence of fitting a wide view onto a flat rectangular image while keeping straight lines straight.
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