IMWRITE followed by IMREAD Changes Pixel Values

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)

Answer 1

[Amith Kamath]

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.

Answer 2

[Image Analyst]

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.