MATLAB Answers

Image display with uint8 and double

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Mohsin Shah
Mohsin Shah on 20 Mar 2018
Commented: Anindya Banerjee on 17 Dec 2019
Can someone explain why the following image, 'yinyang.png', is displayed differently when I use uint8 and double in the imshow function?
I = imread('yinyang.png');
figure(1), imshow(I); title('image displayed with uint8')
figure(2), imshow(double(I)); title('image displayed with double')
The original image displayed in Windows Photo Viewer and the two figure(1) and figure(2) are attached.

Accepted Answer

Stephen
Stephen on 20 Mar 2018
Edited: Stephen on 11 Sep 2019
It seems that you have a "binary" image with values 0 and 1, which is stored as uint8.
  • Because floating-point images are assumed to contain values between 0 and 1 the double image displays those colors as black and white.
  • But for the uint8 image the values are assumed to be from 0 to 255, so those two colors are shown as black and very-dark-gray (indeed, the symbol is just visible in your screenshot).
You can probably use imshow's optional input argument to specify the (non-default) range:
imshow(double(I),[0,255])
imshow(I,[0,1])
See also:
Addendum: the PNG standard supports 1-bit (i.e. binary) images, which MATLAB imports as logical images. Logical images are displayed as black-and-white.
  4 Comments
Anindya Banerjee
Anindya Banerjee on 17 Dec 2019
@ Stephen Cobeldick but inthe case of double, why the image turns out to be inverse? i.e white part of the image becomes black and black part becomes white?

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