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Crop a circle region from an image faster?

Shaohui Yin

Posted 5 years ago

First, I used the Outer function to generate an image. img = Abs[Cos[\[Pi]^2 Outer[Plus, Range[-1, 1, 0.002]^2, 2 Range[-1, 1, 0.002]^2]]]; // AbsoluteTiming Image[img] Then, I set the region outside the unit disk equals 0. This step costs 4.6045 seconds. {Nx, Ny} = Dimensions[img] imgCircle = Table[If[(i - Nx/2)^2 + (j - Ny/2)^2 > (Nx/2)^2, f[i, j] = 0, f[i, j] = img[[i, j]]], {i, 1, Nx}, {j, 1, Ny}]; // AbsoluteTiming Is there a faster way to get the round sub-area of an image?

First, I used the Outer function to generate an image.

img = Abs[Cos[\[Pi]^2 Outer[Plus, Range[-1, 1, 0.002]^2, 2 Range[-1, 1, 0.002]^2]]]; // AbsoluteTiming
Image[img]

enter image description here Then, I set the region outside the unit disk equals 0. This step costs 4.6045 seconds.

{Nx, Ny} = Dimensions[img]
imgCircle = Table[If[(i - Nx/2)^2 + (j - Ny/2)^2 > (Nx/2)^2, f[i, j] = 0, f[i, j] = img[[i, j]]], {i, 1, Nx}, {j, 1, Ny}]; // AbsoluteTiming

enter image description here Is there a faster way to get the round sub-area of an image?

POSTED BY: Shaohui Yin

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Szabolcs Horvát

Posted 5 years ago

Try im Image@DiskMatrix[ImageDimensions[im]/2, ImageDimensions[im]] assuming `im = Image[img]`.

POSTED BY: Szabolcs Horvát

Henrik Schachner

Henrik Schachner, Radiation Therapy Center, Weilheim, Germany

Posted 5 years ago

I did not do any timings, but maybe this is pointing into the right direction. I am applying a mask made out of a graphics: img = Image@ Abs[Cos[\[Pi]^2 Outer[Plus, Range[-1, 1, 0.002]^2, 2 Range[-1, 1, 0.002]^2]]]; dims = ImageDimensions[img]; mask = Image[ Graphics[{White, Disk[{0, 0}, Min[dims]/2]}, Background -> Black, PlotRangePadding -> None], ImageSize -> dims]; imgCrop = img mask

I did not do any timings, but maybe this is pointing into the right direction. I am applying a mask made out of a graphics:

img = Image@
   Abs[Cos[\[Pi]^2 Outer[Plus, Range[-1, 1, 0.002]^2, 
       2 Range[-1, 1, 0.002]^2]]];

dims = ImageDimensions[img];
mask = Image[
   Graphics[{White, Disk[{0, 0}, Min[dims]/2]}, Background -> Black, 
    PlotRangePadding -> None], ImageSize -> dims];

imgCrop = img mask

POSTED BY: Henrik Schachner