Increase speed of imwarp

Question

Jaime 2014-3-7

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https://ww2.mathworks.cn/matlabcentral/answers/120556-increase-speed-of-imwarp

回答： Kees de Kapper 2018-3-21

Dear Matlab community

I have been using imwarp to spatially transform CT-images along with an upscaling step. I would like to optimize my code and I've found that imwarp is taking a lot of time for my needs. Since I need to upscale one of the images by about 2x2x3 in the x,y, and z direction, respectively, the function ends up taking around 10 minutes per image. After doing a profile check it is actually interp3 the one function inside imwarp that consumes most of the time. I wonder if there are ways to speed imwarp like using parallel computing or other alternatives.

Best regards, Jaime

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Igor Reidler 2015-8-23

Hi Jaime, I'm facing a similar situation. Was wondering if you had any progress using parallel computing toolbox, GPU computing, or other?

Thanks, Igor.

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Answer 1

Matt J 2015-8-23

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在 MATLAB Online 中打开

IMWARP seems like the wrong tool for upsampling images. griddedInterpolant is probably smarter, in the sense that it knows that the upsampling can be done separably, and hence more efficiently:

      [m,n,p]=size(CTVolume);
      gridVectors={linspace(1,m,2*m),...
                   linspace(1,n,2*n),...
                   linspace(1,p,3*p)};
      F=griddedInterpolant(CTVolume);
      newImage=F(gridVectors);

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Answer 2

Kees de Kapper 2018-3-21

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https://ww2.mathworks.cn/matlabcentral/answers/120556-increase-speed-of-imwarp#answer_311214

Dear all,

I know this thread is a bit "old" but I've got a similar question. I'm using imwarp for extracting a 2D image from a 3D dataset but with the use of a 3D transformation.

What I experienced is that the speed of imwarp does not depend on the size of the resample output but on the size of the input image. This surprised me a lot and implies a very inefficient implementation.

I found by searching the web, the function tformarray that I might use as well. Using this function the calculation time is reduced with a factor more than ten. I find this very surprising as I expect the imwarp function is build on top of the tformarray-function (correct me if I'm wrong). Do I make a mistake?

The disadvantage is that when using tformarray, I have to construct a tmap_B that reflects the pixel index corresponding to the axis coordinates for both input and resample axis. Although this might be trivial, is there a in-build Matlab function that can do the job?

I'm looking forward to your comments.

Many thanks in advance,

Kees