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Question regarding strange outputs from histogram plot

3 visualizaciones (últimos 30 días)
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])

Respuesta aceptada

Benjamin Großmann
Benjamin Großmann el 30 de Abr. de 2021
Editada: Benjamin Großmann el 30 de Abr. de 2021
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')
  4 comentarios
Teshan Rezel
Teshan Rezel el 30 de Abr. de 2021
Hi @Benjamin Großmann thanks for this! The reason I used imhist instead of histogram is because I wasn't aware of how to plot histogram() outputs on one graph, which I need to do for comparative purposes. Is there a way around this?
Benjamin Großmann
Benjamin Großmann el 30 de Abr. de 2021
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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