imnoise(I,'salt & pepper',D)

Question

Alex Dashevsky 2017-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/340018-imnoise-i-salt-pepper-d

回答： Image Analyst 2017-5-12

I don't understand how I know how many pixels are black and how many white ? salt=white ? pepper=black ?

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Adam 2017-5-12

Does it matter which is which for the noise? It's just a boolean, on or off effectively.

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Answer 1

Image Analyst 2017-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/340018-imnoise-i-salt-pepper-d#answer_266804

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Try this to measure what it produced:

numBlackPixels = nnz(grayImage == 0)
numWhitePixels == nnz(grayImage == 255)

Because the help says "J = imnoise(I,'salt & pepper',d) adds salt and pepper noise to the image I, where d is the noise density. This affects approximately d*numel(I) pixels. The default for d is 0.05." then (numBlackPixels + numWhitePixels)/numel(grayImage) should approximately equal the value of d you used. I think it's safe to assume the proportion of black pepper noise and white salt noise should be about the same - 50% of each type.