How does imflatfield work?

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Julia Kelly on 12 Nov 2019

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Edited: DGM on 2 Oct 2021

imgtemp20190829_081610.csv

What formula does the imflatfield function use when used with a matrix as input?

For example, I have an image of surface temperature (attached) = bad_img. If I apply

corr_img = imflatfield(bad_img,100);

How can I reproduce corr_img without using imflatfield? I know that the gaussian filter can be generated using

iblur=imgaussfilt(bad_img, 100);

但是下一步是什么？

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William Nitsch on 2 Oct 2021

iout = iin * mean（gaussian_blurred_img）/gaussian_blurred_img

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DGM on 2 Oct 2021

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Edited:DGM on 2 Oct 2021

William's comment is close. Probably close enough to be useful, but not quite exactly the same as what imflatfield() does.

                              A = imread('printedtext.png');
                             
                              Sigma = 30;
                             
                              ％这是参考
                             
                              output1 = imflatfield(A,sigma);
                             
                              % this is a replication of the behavior
                             
                              A = im2single(A);% non-double images are converted to single
                             
                              %这是默认的过滤器的尺寸,但是它可以be set explicitly too
                             
                              blurred = imgaussfilt(A,sigma,'填充','symmetric','filtersize',2*ceil(2*sigma)+1);
                             
                              output2 = A*mean(A(:),'omitnan')./blurred;% mean of A, not of blurred image
                             
                              output2 = im2uint8（output2）;
                             
                              immse(output1,output2)% show that the results match
                             
                                ans = 0

Bear in mind that if you want to exactly replicate the behavior, there are other things that happen (e.g. dealing with NaNs and Inf) that need to also be considered. You can always just open imflatfield() and read it.

EDIT: oof. This wouldn't be the first time I absentmindedly answered a dead question...

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