How to plot a histogram from 0-255

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Changoleon
Changoleon 2016-9-6
评论： Guillaume 2017-9-11
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.

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采纳的回答

Thorsten
Thorsten 2016-9-6
编辑：Thorsten 2016-9-6
I = imread('cameraman.tif');
imhist(I)
shows values from 0 to 255. Do you change I after imread and before imhist?
  2 个评论
Changoleon
Changoleon 2016-9-6
actualy this is how I code: a = double(imread('Wk1_O5_Image017.tif')); is it double?
Thorsten
Thorsten 2016-9-6
Either use
I = imread('yourfile.tif');
imhist(I);
or as Guillaume suggests,
I = im2double(imread('yourfile.tif'));
imhist(I)

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更多回答（2 个）

Guillaume
Guillaume 2016-9-6
See the documentation on image classes.
Most image processing functions expect double images to be in the range 0-1. If the range is 0-255, matlab expects it to be a uint8 image.
a = im2double(imread('yourimage'));
imhist(a);
should solve your problem. Or keep the image as uint8.
dhafer alhajim
dhafer alhajim 2017-9-11
编辑：dhafer alhajim 2017-9-11
if you want the value and the range from 0 to 255 a = im2double(imread('your image')); h=uint8(imhist(a));
  1 个评论
Guillaume
Guillaume 2017-9-11
@dhifer alhajm
I don't see the point in answering a question that is over a year old. Particularly as your answer is totally incorrect. Because of the call to im2double, the input range is 0-1. As for the uint8(imhist), that's completely silly, any histogram count above 255 will be clamped to 255.
Here's an example:
a = uint8(repelem([0 63 127 255]', [20 40 60 80], 200));
imshow(a);
This is an image with 4000 counts of intensity 0, 8000 of intensity 63, 12000 of intensity 127 and 16000 counts of intensity 255.
>>h = uint8(imhist(im2double(a)))
>>h(1) %counts of intensity 0
ans =
255
>>h(end) %count of intensity 255
ans =
255
The count of all intensities present in the image is 255 according to you.

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