Plotting histogram of image data present in a stack

Hi All,

I have looked at the examples shown here to underetand how to plot histogram of a single image data. But

it's not clear to me how the data in a stack can be plotted.

For exmaple, I tried

f = "Test_Image.tiff";
img_data = imfinfo(f);
imhist(img_data)

test_image stack.

This returns

double, uint8, int8, logical, uint16, int16, single, uint32, int32

Instead its type was struct.

Any suggestions?

Answer 1

[Ameer Hamza]

iminfo just read the metadata of the image. Use imread() to read the image as matrix

f = "Test_Image.tiff";
img_data = imread(f);
imhist(img_data)

If it is an rgb image, then first convert it to grayscale too

f = "Test_Image.tiff";
img_data = rgb2gray(imread(f));
imhist(img_data)

[Deepa Maheshvare]

Could you please let me know if `imread()` can be used to read an image stack? I have tested it before and it reads only the first image of the stack which is also mentioned in the documentation (https://in.mathworks.com/help/matlab/ref/imread.html?s_tid=srchtitle)

[Ameer Hamza]

Yes, you can use

img_data = imread(f, 'all');

to read all frames. But then how to you want to do imhist()? Do you want to plot histogram of each image individually.

[Deepa Maheshvare]

"But then how to you want to do imhist()? Do you want to plot histogram of each image individually".

No, I would like to generate the histogram in a single plot. May I know how to do this?

[Ameer Hamza]

Try this

f = "Test_Image.tiff";
img_data = imfinfo(f);
imgs = cell(1, numel(img_data));
for i = 1:numel(img_data)
    imgs{i} = imread(f, i);
end
imgs = cat(3, imgs{:});

imhist(imgs(:))

[Deepa Maheshvare]

Thanks a lot. This helps! I would also like to know if it is possible to get the stats like mean, sd, mode, binwidth (I checked that the default bin is 256) , min and max and count?

[Ameer Hamza]

By default imhist() uses 256 bins. You can get the counts using output of imhist()

[binCount, binLoc] = imhist(imgs(:));

To get min and max values

mean(imgs(:))
min(imgs(:))
max(imgs(:))