Histogram from masked area of grayscale picture

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Anders Jensen
Anders Jensen am 18 Jun. 2019
Bearbeitet: Steven Lord am 18 Jun. 2019
Hello!
I want to make a histogram from masked area of a grayscale picture. I've tried this:
maskedImage = bsxfun(@times, grayImage, cast(mask, 'like', grayImage));
histogram(maskedImage(mask), 256, 'EdgeColor', 'none')
But it keeps saying: "Array indices must be positive integers or logical values". There are no negative integers and the mask only contains 0 and 1.
Hope you can help! :-)

Akzeptierte Antwort

Steven Lord
Steven Lord am 18 Jun. 2019
Bearbeitet: Steven Lord am 18 Jun. 2019
When performing indexing, there is a difference between a logical array and a double array containing only 0 and 1. The former works and performs logical indexing, the latter does not work and throws an error because there's no such thing as element 0, row 0, column 0, page 0, etc. of an array in MATLAB.
x = 1:10
L = mod(x, 2) == 0
D = double(L)
onlyEvens1 = x(L) % Works
onlyEvens2 = x(D) % Errors
If mask is a double array containing just 0's and 1's you'll need to convert it into a logical array to use it for indexing. The easiest way to do this is to call the logical function on it.
L2 = logical(D)
isequal(L, L2) % True
onlyEvens3 = x(L2)

Weitere Antworten (2)

Image Analyst
Image Analyst am 18 Jun. 2019
Attach a .mat file containing your grayImage and mask.
Alternatively, just do
histogram(grayImage(mask), 256, 'EdgeColor', 'none')

Anders Jensen
Anders Jensen am 18 Jun. 2019
Thanks for your answer! It still says "Array indices must be positive integers or logical values".
I have attached the .mat file and the grayscale image :-)

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R2019a

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