RE: [WM]: 2D DWT TRANSFORM

["Dr. Fatih Kurugollu" <f.kurugollu@qub.ac.uk>]

Hi,


You can use colormap(gray)  to display the images in gray level after image(). However using image() is not a good idea to display
the subbands of a wavelet decomposition. The subbands will probably have values out of [0..225] gray level range. I recommend you to
use imagesc() which scales the values automatically to [0..255].  Therefore  usage of "imagesc([ca,ch;cv,cd]), colormap(gray)" will
solve the problem. 

Cheers,

Fatih

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Dr. Fatih KURUGOLLU

Lecturer

School of Electronics, Electrical and Computer Science Queen's University, Belfast

18 Malone Road, Belfast, BT7 1NN, UK

T: +44 (0) 28 9097 4628

+44 (0) 28 9097 1824

F:+44 (0) 28 9097 4879

E: f.kurugollu@qub.ac.uk

kurugol@yahoo.com

W: www.cs.qub.ac.uk/~f.kurugollu

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-----Original Message-----
From: watermarking-owner@watermarkingworld.org
[mailto:watermarking-owner@watermarkingworld.org] On Behalf Of Eyneen Altaf
Sent: Tuesday, March 06, 2007 10:45 AM
To: watermarking@watermarkingworld.org
Cc: im943084@mail.cpu.edu.tw
Subject: [WM]: 2D DWT TRANSFORM

Dear advisor,

I have a question pertaining to applying DWT transform to gray scale images.
I read a  grayscale gif image and then implement the
dwt2() transform in MATLAB.I am using the 'haar'filter. When i plot the image using the approximation and detail coefficients as in
'image([ca,ch;cv,cd]), i get colored subbands. How can i avoid this coloring of the subbands. On applying the
idwt2() transform the image that gets reconstructed is also colored. I wish to avoid this. Please advise.

Regards,
Annie


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