Fisheye / Lens Distortion
One control covers both directions of lens distortion. Positive strength magnifies the centre and compresses the edges — the bulge you get from a fisheye or a GoPro. Negative strength does the reverse, pinching the middle and stretching the corners, which is what corrects an image already shot on a wide lens.
Drop images here
PNG, JPG, WebP — multiple files allowed
Why the corners go empty
The model is the standard radial one: a pixel at distance r from the centre samples the source at r × (1 + k·r²), with distance normalised so the corner is 1. At positive k the outer pixels reach beyond the source image and there is nothing there, so the corners come out transparent. That is the honest result — a fisheye lens has a circular image circle, and squares do not survive it.
There are two ways out. Zoom above 100% scales the sampling inward so the whole output frame falls inside the source, at the cost of cropping — this is what camera software calls "distortion correction with auto-crop", and 115–130% usually covers a 40% bulge. Or set the edge mode to stretch, which clamps out-of-range samples to the nearest real pixel; that fills the corners with smeared streaks, which reads as deliberate on an abstract image and obviously wrong on a photograph.
Correcting rather than adding
To undo distortion in a photo, use a negative strength roughly matching what the lens added. GoPro and similar action cameras land around −25 to −40 in these units; a phone ultrawide is closer to −10 to −18. Judge it on straight lines near the frame edge — a door frame, a horizon, the join between wall and ceiling. When those stop bowing, you are close.
This is a one-parameter approximation, not a real lens profile. Actual correction uses several polynomial terms and knows the specific lens, so a single term will straighten the middle of an edge while leaving the extreme corners slightly off. For a quick visual fix that is fine; for architectural or measurement work it is not.
FAQ
Why is the result soft?
Bilinear resampling, plus genuine magnification. At the centre of a strong barrel warp you are enlarging a small patch of the source to fill a large area, so there is simply less detail there than the output pixels can hold. Distorting a larger source and then downscaling gives a crisper result.
Can I put the centre somewhere other than the middle?
Not currently — the distortion is centred on the image. Crop first with Crop so the point you care about is central, then apply the warp.
Is this the same as Zoom?
No. Zoom scales uniformly; every part of the image changes size by the same factor. Here the scale factor varies with distance from the centre, which is what creates the curvature.
What about a tunnel or sphere effect?
Push the strength past about 70 with zoom at 100 and you get close to a sphere sitting in an empty frame. Swirl and Kaleidoscope are the other two radial warps here and combine well with this one.