Re: [SIP-users] imshow problem in 0.3.1

[Ricardo F. <rf...@if...>]

On Tue, 17 Feb 2004, Charlls Quarra wrote:

>  Hi,
>
>  I have scilab 2.7 on RH9, i loaded SIP doing exec
> loader.sce, then i did
>
>
> --> A=imread('somegrayscaleimage.jpg');
> --> imshow(A)
>
> the graphics window shows empty!
>
>  is this a known problem or its something else?

Hi,

SIP 0.3.1 changed  the way it treats image ranges.

The grayscale image you read is actually an indexed image with gray
colormap.

The correct way to read/display it would be:

[A,map] = imread('grayimage.jpg');
imshow(A,map);

The matrix A is not an image itself; its entries are indexes to the colormap
"map". Therefore, indexes range from 1 to NC, where NC is the number
of colors of the image.

if you do a simple

imshow(A)

Then imshow will assume 0 is black, 1 is white, and all above 1 is
white, so that's why your image is all blank.

Alternatively, you may:
A = imread('grayimage.jpg');
imshow(A,256);

OR

imshow(A/maxi(A));

OR  even

imshow(A,[]);

The last command rescales A to occupy the 0-1 range.

Ricardo.

--
  Ricardo Fabbri, Cybernetic Vision Research Group, USP, Brazil.
  WEB: cyvision.if.sc.usp.br/~rfabbri   ICQ: 208974212

  "With pain and suddeness is how Real Offsprings are born. But they
  must result from intense pleasure and a long period of development."