Weird Imhist beahviour seen

Hi, ive been tearing my hair out all morning. I want to plot the histogram of an image. I normally use im hist. My images are 3 12 bit images that are summed, hence the max value can be 3*4095=12285. It appears my histogram is defaulting to 16 bit values.

This is my code:

IM = imread(file);
IM1=double(IM);
[maxval,idx]=max(IM1(:))  % determine number of bins (of width = unity)
maxval= double(maxval);
[counts,x] = imhist(IM,maxval);  
figure
stem(x,counts,'b', '.');
counts(maxval)   %check the max intensity

First of all, counts(maxval) returns zero, and here is the histogram stem plot - defaulting to 65535 levels. I want to have 1-12285 levels.

Answer 1

[Image Analyst]

Try this:

grayImage = imread(file);
maxGrayLevel = max(grayImage(:))  % determine max gray level.
[counts, grayLevels] = imhist(grayImage);
bar(grayLevels, counts, 'Color', 'b');
xlim([0, maxGrayLevel)]; % Specify range of x axis.

Let me know how it works.

[Jason]

OK, so you don't suppress the unwanted gray levels, but use display via xlim to view only whats wanted.

Yes this works, thanks IA!

[Image Analyst]

You're welcome. Can you go ahead and officially mark the answer as "Accepted" then? Thanks in advance.

Answer 2

[DGM]

I don't know where everyone is getting uint12-scale images, but I guess it's a thing. I posted an example which demonstrates three ways of representing improperly scaled images (uint12 in uint16, and int12 in int16) using imhist() and other tools.

https://www.mathworks.com/matlabcentral/answers/159792-problem-with-imhist-method#answer_1460156

[Jason]

Thankyou!

[DGM]

Oh wow. I didn't even notice both threads were yours. I certainly didn't expect a prompt reply!

You're welcome.