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

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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.
  2 Commenti
Roman Boldin
Roman Boldin il 22 Gen 2020
Hello, do you still have the code of for and loop?
Image Analyst
Image Analyst il 22 Gen 2020
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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Andrew Bliss
Andrew Bliss il 13 Giu 2016
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.
asdf=imread('example.tif');
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)
  2 Commenti
Nut
Nut il 14 Giu 2016
Thank you very much for your answer, it may be a good way. I'll compare this with the for loop.
Nut
Nut il 14 Giu 2016
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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Image Analyst
Image Analyst il 14 Giu 2016
Modificato: Image Analyst il 14 Giu 2016
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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