MATLAB: How to plot a histogram from 0-255

imhist

I use img1=imread function to load my image into matlab. The image is 512by512 and the intensity range is 0-255. However the histogram of my image ( which I use imhist(img1) to plot it) has values only at 0 and 1. How is that? I mean when I take a look at the array of my picture, I see numbers varying from 0-255. Is it because I am using imhist? Any idea would be appreciated. and sorry if the question might be very basic for some of you.

Best Answer

I = imread('cameraman.tif');
imhist(I)

shows values from 0 to 255. Do you change I after imread and before imhist?

Related Solutions

MATLAB: How to count the number of occurrences of pixel intensities in an image without using for loop

im = imread('image.jpg');
Rhist = imhist(im(:,:,1));
Ghist = imhist(im(:,:,2));
Bhist = imhist(im(:,:,3));

Or using histcounts:

Rhist = histcounts(im(:,:,1),0:256);
Ghist = histcounts(im(:,:,2),0:256);
Bhist = histcounts(im(:,:,3),0:256);

MATLAB: Imshow(uint8(imagematrix)) and imshow(int8(imagematrix)) gives different results although pixel values are between 0-255

>> uint8(255)
ans =
  uint8
   255
>> int8(uint8(255))
ans =
  int8
   127

When you int8() data that is in the range 0 to 255, all values that are 128 or more are turned into 127, the maximum value for the range.

When you imshow() an int8 image, it notices that it is int8, and scales the colors to run from -128 to +127, with 0 being the middle color and 127 being the brightest color. But since you started with uint8 you do not have any values that are negative, and you will probably have a number of locations that int8() changed from being 128 or more into 127 which is maximum brightness for int8.

Best Answer

Related Solutions

MATLAB: How to count the number of occurrences of pixel intensities in an image without using for loop

MATLAB: Imshow(uin​t8(imagema​trix)) and imshow(int​8(imagemat​rix)) gives different results although pixel values are between 0-255

Related Question

MATLAB: Imshow(uint8(imagematrix)) and imshow(int8(imagematrix)) gives different results although pixel values are between 0-255