How to change the amount of the histogram?

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Faranak on 25 Feb 2014
Answered: Jos (10584) on 26 Feb 2014
Hello all,
I have an image and I want to plot the histogram of the image,but the histogram is unusual,maybe it is because lots of amount of the pixels have the value 1. Is there anything that I can do so that I can put the range of the histogram became between [2,989],, 989 is the maximum pixel value.for the histogram I use this command: I don't know why the amount of the value for the histogram are until 3*10^3 In the picture there are lots of value between [2,989],I don't know why it doesn't show them,how can I show the value for other pixel values in the histogram. figure,imhist(a)

Answers (3)

Image Analyst
Image Analyst on 25 Feb 2014
This is a double image, isn't it? Not an integer image. Do this:
and tell me what it says. I suspect it's double, and that's the problem. If it's double, then imhist thinks that all the numbers should be between 0 and 1 and if you have any bigger than 1 it clips to 1. You'll have to use im2double() or just use hist instead of imhist:
pixelCounts = hist(a(:), 16384);
bar(pixelCounts, 'BarWidth', 1);
Faranak on 26 Feb 2014
it's not working. what is 16384 related to?
Image Analyst
Image Analyst on 26 Feb 2014
Thats the number of bins. It's the mas to make sure you get just one graylevel per bin. If you don't put that then the default is only 10 bins I believe, which gives a pretty chunky histogram.

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Jos (10584)
Jos (10584) on 25 Feb 2014
use HISTC to specify the bins
Faranak on 26 Feb 2014
it gives me this error .
Error using histc Not enough input arguments.
Jos (10584)
Jos (10584) on 26 Feb 2014
Did you read the documentation of histc? It requires two arguments ...

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Jos (10584)
Jos (10584) on 26 Feb 2014
I will spell it out for you, provided that you read the documentation , ok?
% let X be your image with values between 2 and M, and 1 being background
doc histc
maxX = max(X(:))
edges = 2:maxX ;
n = histc(X(:),2:maxX) ;
bar(edges,n) ;

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