IMWRITE followed by IMREAD Changes Pixel Values

Question

Ajmal 2013-8-19

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采纳的回答： Amith Kamath

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I have an image matrix

aa 150x200x3 720000 double

With pixel values 0-255

Why does this test fail :

imwrite(aa, 'aatest.png');
aanew = imread('aatest.png');
isequal(aa, aanew)

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Answer 1

Amith Kamath 2013-8-19

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编辑：Amith Kamath 2013-8-19

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I tried this, and I realized that ISEQUAL compares a DOUBLE and UINT8, which quite obviously does not return true.

 p = rand(150,200,3);
 imwrite(p,'test.png');
 pnew = imread('test.png');
 isequal(p,pnew)

if you really want to check equality,

isequal(im2uint8(p),pnew)

is the way to go.

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Answer 2

Image Analyst 2013-8-19

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I don't believe PNG is meant for doubles, though I could be wrong. Anyway I never try to save color images while in a double class unless it's to a mat file. Try casting your aa array to uint8 before you save it out. I think that's really what you want and intended anyway.