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Re: usage of imread.m in octave

From: Daniel J Sebald
Subject: Re: usage of imread.m in octave
Date: Thu, 15 Jul 2004 03:41:17 -0500
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.2) Gecko/20021120 Netscape/7.01

From what I've seen, only gray scale and color palettes (i.e., "colormap") currently work in Octave. To show a color image, you need independent primary color components, e.g., RGB. So first, you can't use

X = imread('testimage.jpg');

because X can't have RGB. (Unless it were a 3 dimensional matrix, which I think it isn't.) So you need something like the RGB variant:

[r,g,b]= imread( fname );

Then you can do an


But, currently here is what imshow() does for the RGB

elseif (nargin == 3)
[a1, a2] = rgb2ind (a1, a2, a3);
colormap (a2);

i.e., converts to an indexed image. I believe in general that can only be an approximation.


Ole Jacob Hagen wrote:


Octave-Forge has imread.m as part of the signal processing module inside.
I am using imread like this:
X = imread('testimage.jpg');
The testimage.jpg can be found here

And imshow(X), will then give me a black-white image, but it's supposed
to be a colour image. I'd like to have colours.
Does imshow or image work with colour?

I would like to have working example script, if anyone has a working example...if it's possible....

Why doesn't this works? Where does it fails, what is wrong, and does
someone have a fix for this?

Oplot-developers have implemented the same thing, but the image popups
in Oplot instead of ImageMagic. :-)

We can do:

Line, Image, Axes, Figure.
Soon Patch and Surface.

Then we are heading for UIControl...


Ole J.


Dan Sebald
email: daniel DOT sebald AT ieee DOT org
URL: http://acer-access DOT com/~dsebald AT acer-access DOT com/

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