efficient use of extracting mean over segments

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Sukuchha 2013-2-20

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Hello, I have image (Iseg) where i have number of segments. Each segments is represented by unique number in Iseg. The segments are around (50000). I have another image(Idata) which is same size that of Iseg. For every segment in Iseq i want to extract mean value of segments from Idata.

Rightnow i am using like this

NumRegion = max(max(Iseg));
mean_magnitude = zeros(size(Iseg));
for i=1:NumRegion
    [iIndList] = find(Iseg == i);
    mean_magnitude(iIndList) = mean(Idata(iIndList));  
end

It works fine, but the problem is that it takes a long time. about 10 mins in my machine. Is there a effecient way to do it.

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Image Analyst 2013-2-22

编辑：Image Analyst 2013-2-23

I'm not sure either. Is a "segment" a blob in a binary image? And he wants the mean gray level of a gray level image for each blob region? Sounds like Iseg is a "labeled" image like you'd get from bwlabel (connected components labeling) where each blob has a unique ID number assigned at every pixel in the blob.

Sukuchha 2013-2-25

Image Analyst, you are right. Iseg is a grayscale image, where each blob has a unique ID number assigned at every pixel in the blob.

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Answer 1

Image Analyst 2013-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/64297-efficient-use-of-extracting-mean-over-segments#answer_76174

编辑：Image Analyst 2013-2-22

在 MATLAB Online 中打开

Do you, by chance, mean this:

measurements = regionprops(Iseg, Idata, 'MeanIntensity);
allMeanIntensities= = [measurements.MeanIntensity];

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Sukuchha 2013-2-25

i had a look at intlut before but couldnot figure out how to use it. Could you please show one example(or pseudo code)?

Image Analyst 2013-2-25

在 MATLAB Online 中打开

Something like (untested)

newImage = intlut(labeledImage, allMeanIntensities);

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Answer 2

Jan 2013-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/64297-efficient-use-of-extracting-mean-over-segments#answer_76175

在 MATLAB Online 中打开

At first you can cleanup the loop a little bit using logical indexing:

NumRegion      = max(max(Iseg));
mean_magnitude = zeros(size(Iseg));
for i = 1:NumRegion
  iIndList = (Iseg == i);
  mean_magnitude(iIndList) = mean(Idata(iIndList));  
end

I assume accumarray is faster. I'd try to run a loop over Iseq instead also, but I cannot test it due to the absence of test data. It might be helpful if you post some, e.g. produced by some rand calls.

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Sukuchha 2013-2-25

编辑：Sukuchha 2013-2-25

The looping is much slower. The code given by image analyst calculated mean intensities over each blob in much faster way but problem now to to make a raster image out of it. measurements = regionprops(Iseg, Idata, 'MeanIntensity); allMeanIntensities= = [measurements.MeanIntensity];

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