Re: {JPEG}Discrete Cosine Transformation

From: Gernot Hoffmann (hoffmann_at_fho-emden.de)
Date: 07/12/04


Date: 12 Jul 2004 09:10:49 -0700

mintiSPAMBLOCK@yahoo.com (Minti) wrote in message news:<e87fc4b0.0407111151.32f29a93@posting.google.com>...
> Hi there,
>
> I am doing some research on JPEG, being from a non-mathematical
> background I am having quite some difficulty in understanding the
> basic concepts of DCT. I have searched the web for couple of days but
> nothing concrete. A lot of articles just refered to Rao's book for
> understanding DCT, unfortunately I can't find it anywhere nearby. I
> will be thankful if anyone could either explain the _basis_ and
> _advantages_ of DCT or provide some pointers on web, pointers to
> articles on ACM also welcomed.
>
>
> Thanks.

Minti,

in at least one of the URLs in the other posts the DCT is considered
as the cosine part of the discrete Fourier series. Thatīs wrong.
The cosines in the DCT have a phase shift.
Some illustrations are here:
http://www.fho-emden.de/~hoffmann/jpeg131200.pdf
The graphics may help to understand the SHAPES of the functions in the
function system.

Best regards --Gernot Hoffmann



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