[XviD-devel] why DCT image/video compression?

Christoph Lampert chl at math.uni-bonn.de
Wed Sep 22 09:01:43 CEST 2004


On Wed, 15 Sep 2004, prabhakar p wrote:

> Hi Guys,

>      Hope ur doing fine there.Can anybody let me know, what all the
>      reasons DCT is preferred over other Transformations in image/video
>      compression techniques.

Like _what_ other transformations? 

DCT is a classical approximation of PCA, and very succesful for it 
computational efficiency and very good energy compression property. 
DCT has been used for several decades, and people and device know how to 
work with it. The only alternatives, which only came up recently are 

* integer approximations of DCT like in H.264 or WMV9 (IIRC). Those are 
  somehwat less effective, but can be done exact to the bit on PCs, which 
  avoids error drift. So, it's not really a different approach, only an 
  implementation better suited to PCs. 

* wavelet transforms, which might be "the future", but which are 
  mathematically more difficult, and Motion Estimation has many more 
  problem than in blockbased DCT. Rumors are that RealVideo uses Wavelets, 
  but I never saw anything concrete about it. I haven't even heard rumors 
  about hardware for those. 

DCT was first and works well, and so far, it's the method of choice (i.e.  
MPEG2, MPEG4, JPEG, DV), until the new standards really kick in (if they
ever do).

gruel



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