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Question regarding strange outputs from histogram plot

조회 수: 2(최근 30일)
Teshan Rezel
Teshan Rezel 2021년 4월 30일
댓글: Benjamin Großmann 2021년 4월 30일
Hi folks,
I have an image which is mostly black, with specks of purple. When I plot the RGB histogram for the image, I get an sharp line in the blue region but zero elsewhere, which I don't think is correct.
Can you please advise me on where I've gone wrong?
Thanks
R3=imhist(img3(:,:,1));
G3=imhist(img3(:,:,2));
B3=imhist(img3(:,:,3));
[pk31, locs31] = max(R3);
[pk32, locs32] = max(G3);
[pk33, locs33] = max(B3);
str31 = strcat('\leftarrow', num2str(locs31));
str32 = strcat('\leftarrow', num2str(locs32));
str33 = strcat('\leftarrow', num2str(locs33));
figure
hold on,
plot(R3,'r'),
text(locs31, pk31, str31),
plot(G3,'g')
text(locs32, pk32, str32),
plot(B3,'b'),
text(locs33, pk33, str33),
legend(' Red channel','Green channel','Blue channel','Location','best');
hold off,title('Mask 2 - RGB Histograms');
xlim([0 20])
ylim([0 5000])

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Benjamin Großmann
Benjamin Großmann 2021년 4월 30일
편집: Benjamin Großmann 2021년 4월 30일
If you do not provide any code, it is hard to tell what went wrong here. If I use your image, everything looks fine:
imageURL = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/602390/image.jpeg';
img = imread(imageURL);
tiledlayout(3,1)
bins = [0:255];
nexttile()
histogram(img(:,:,1), bins)
title('R')
nexttile()
histogram(img(:,:,2), bins)
title('G')
nexttile()
histogram(img(:,:,3), bins)
title('B')
  댓글 수: 4
Benjamin Großmann
Benjamin Großmann 2021년 4월 30일
the command "hold on" that you used, works on the axes and can also be used for histograms. It sets the axes property "NextPlot" to "add" instead of "replace". I prefer to set the property instead of "hold on"
imageURL = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/602390/image.jpeg';
img = imread(imageURL);
bins = [0:255];
fig = figure();
ax = axes('Parent', fig, 'NextPlot', 'Add');
histogram(img(:,:,1), bins, 'DisplayName', 'Red Channel')
histogram(img(:,:,2), bins, 'DisplayName', 'Green Channel')
histogram(img(:,:,3), bins, 'DisplayName', 'Blue Channel')
legend(ax, 'show')

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