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[Octave-bug-tracker] [bug #44118] imwrite saves wrong pixel values into

From: Carnë Draug
Subject: [Octave-bug-tracker] [bug #44118] imwrite saves wrong pixel values into jpg file
Date: Thu, 29 Jan 2015 19:47:31 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Firefox/31.0 Iceweasel/31.4.0

Follow-up Comment #3, bug #44118 (project octave):

You are correct, the intensity values on the saved image are much lower.

I think I know what may be happening. When an image in GraphicsMagick is
grayscale, the intensity values are stored in the red channels. This is true
for reading and writing.  However, for writing a jpeg grayscale, seems like it
looks into the green and blue channels. These seem to default to zero which is
why it is darker. The whole point of using GraphicsMagick is avoid coder
specific code but seems that it won't do.

Maybe I am wrong about the reason, but the following seems to be a

A = uint8 ([0 50 255; 1 3 6])
file = "new.jpg";  
imwrite (repmat (A, [1 1 3]), file);
B = imread (file)


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