How to apply a different b/w threshold to each row of the image?

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Nut 2016 年 6 月 13 日
コメント済み: Image Analyst 2020 年 1 月 22 日
Hi,
I would convert an image from grayscale to black-and-white using the im2bw function, and I need to apply a different threshold to each row of the image. Which is the most efficient way to do this? Is there a way to avoid the "for" cycle?
Thank you very much.
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Image Analyst 2020 年 1 月 22 日
Roman, it would be something like
[rows, columns, numberOfColorChannels] = size(theImage);
binaryImage = false(rows, columns);
for row = 1 : rows
% Get the threshold for this row - however you do it (I don't know).
thisThreshold = whatever;
% Now threshold/binarize the image for this row only.
binaryImage(row, :) = theImage(row, :) > thisThreshold;
end

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採用された回答

Andrew Bliss 2016 年 6 月 13 日
Depending on the input type of your image, you may be able to just do a simple thresholding operation (as below), otherwise you'll have to delve a little deeper into image processing.
figure,imshow(asdf)
zxcv=rgb2gray(asdf);
figure,imshow(zxcv)
thresh=[50*ones(325,1);150*ones(325,1)]; %here you set the threshold for each row
threshMatrix=repmat(thresh,1,600);
BW=zxcv>threshMatrix;
figure,imshow(BW)
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Nut 2016 年 6 月 14 日
You're right. The execution time with your solution is about 1.6 seconds, instead using im2bw and the for loop it is about 5.1 seconds. Very good idea, thank you again.

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その他の回答 (1 件)

Image Analyst 2016 年 6 月 14 日

No, you'll have to use a for loop. It's not a problem though. It will be very fast. No need to worry about for loops that are only a few thousand iterations.
Why do you need a different threshold for each row anyway?
You might be able to use a different function. There are new binarization functions. See Steve's blog:
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Nut 2016 年 6 月 16 日
I'll try it, thank you!

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