CODEWITHSUNDEEP
matlabimage-processinghistogram
StuckInPhDNoMore
StuckInPhDNoMore

Reputation: 2679

Histogram function imhist() produces a white line with black dots

I want to see the histogram of an image using the built in function imhist() but instead of giving me the expected histogram I am presented with a straight white line.

This is the test image which I am using to create a histogram: http://tenettech.com/content/images/thumbs/0002817_basys2_spartan_3e_250k_gates_fpga_board_600.jpeg

This is the code I am using to get my histogram:

img = imread('test.jpg');
gray = rgb2gray(img);
hist = imhist(gray);
imshow(hist);

This is what I get from imshow(hist);

https://i.sstatic.net/vqnlb.jpg

Its difficult to see properly but with a gray background it is just a white line with the black spot at top.

I was expecting a result like this: http://nf.nci.org.au/facilities/software/Matlab/techdoc/ref/graphiac.gif

Upvotes: 0

Views: 2110

Answers (2)

lennon310
lennon310

Reputation: 12689

Just directly use:

img = imread('test.jpg');
gray = rgb2gray(img);
figure,imhist(gray)
figure, bar(imhist(img))
figure,bar(imhist(img,50))

Upvotes: 1

gevang
gevang

Reputation: 5014

The output of imhist is a vector of counts, not an image (i.e., displaying this 1D vector of numbers as an image through imshow will produce the "black-dots line").

Either use plot (or bar) to display the histogram OR use imhist without any output arguments to get a (default) histogram plot. 

nBins = 100; % 
[counts, x] = imhist(gray, nBins);
figure; bar(x, counts);

figure; imhist(gray, nBins)

Upvotes: 2

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