Hi, I would like to perform the log-polar transform of an image. I tried. I failed. Maybe this is obvious to some of you… First, I deal with the polar transform. The trouble seems to come from a specific type of images using Revise using CoordinateTransformations, ImageTransformation, Plots, Test…

@rveltz , code updated with more wave periods/rings (and using ImageCore): N = 2001; img1 = Gray.([ 0.5*(1.0 + cos(x - y)) for x in LinRange(0,5pi,N), y in LinRange(0,5pi,N)]) img1 = ImageCore.n0f8(img1) heatmap(img1) img2 = OffsetArray(img1, -N÷2:N÷2, -N÷2:N÷2); imgw = warp(img2, tfm) heatmap(imgw)…

Actually, why cant we only see the first band?

@rveltz , not sure how the sampling is done but I think it is inevitable to have leftovers in this type of log-polar mapping, as both input and output from warp are rectangular. See code edited above. PS: btw, why the logarithm is not used in your definition?

it is inevitable to have leftovers in this type of log-polar mapping, Yes, but if you apply the rotation transform, it fills the unknowns with black. Cant we do the same here? PS: btw, why the logarithm is not used in your definition? I could not get it work so I focused first on the polar on…

After some research on this, the results above do not seem to make sense. The Polar-Cartesian transforms should wrap/unwrap images like posted here . The simple code below adapted from Matlab seems to behave as expected for the Polar transform. It seems that you are looking for the inverse (Cartesi…

Mapping something with atan will give coordinates in the range -2 … 2, which is not good for an image. Moreover warp tries to automagically guess the correct dimensions of the output image and this appears to fail for polar transform. Try warp(img0, tfm, (-1000:1000, -1000:1000))

Log-polar transform of an image

General Usage

rafael.guerra December 19, 2020, 12:42pm 7

@rveltz, I am sorry but my knowledge on this topic is small. I would only point out that if we do not offset the array, we get more wavefront rings but seemingly incomplete:
output3

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Log-polar transform of an image

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