MATLAB: Histogram doesn’t work for .png images

imhistpng

hello everyone. I am having trouble with displaying histogram for .png image. the image is grayscale already, so I just use this code.

I=imread('38_training.png');
figure,imhist(I)

but the histogram is.. empty.

any idea why? this is the image i'm trying to show the histagram of.

thank you! please help.

Best Answer

Your image is binary. It only has white and black pixels. Therefore it only has peaks at 0 and 255. Following example show, it has nothing to do it with png file.

im = imread('pears.png');
imhist(im)

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MATLAB: Saving .png images in directory

The counterpart to imread is imwrite, not save. save as you've used it saves all the workspace variable in a mat file (irrespective of the extension you use).

Replace your save by:

imwrite(compositeImage, sprintf('CompsiteImage%d.png', y));

Note that I'm using sprintf to build the filename instead of string concatenation as you'd done. In my opinion, it's more readable. If you're going to use string concatenation, at the very least be consistent in your use of separator. You used a space to separate 'compositeImage' and num2str(y) and a comma to separate num2str(y) and '.png'.

MATLAB: Creating .PNG image from temperature values

I guess you are using saveas() or some other function to save the .png file. They are not suitable for maintaining the resolution. Use imwrite() as shows in the following lines

image = round(rescale(image, 1, 256));
imwrite(image, jet, 'image.png');

Best Answer

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