[theora-dev] VP3 IDCT

[Dan Miller]

I believe they are.  At some point I replaced them with my own functions off the standard texts and I recall there wasn't any noticeable visual problem.  However I can't remember if they were bit-for-bit accurate.

With any DCT/IDCT implementation, the issue of any loss of precision etc. that might cause the encoder's reference decoding to drift from the decoder's has to be considered.  I know we have run into problems like this when porting decode to different platforms.  The only true document for now (until I get my spec together) is the code, so you will have to look at it or at least compare your output to the output of the present decoder.  It's intended to be a pure 32-bit integer implementation if that helps.

I do know (with my usual 99.44% assurance) that the two speedups (DC only & <=10 AC's) are supposed to be numerically identical to the full-on version.

<p>> -----Original Message-----
> From: Mike Melanson [mailto:melanson at pcisys.net]
> Sent: Wednesday, March 05, 2003 11:10 AM
> To: theora-dev at xiph.org
> Subject: [theora-dev] VP3 IDCT
> 
> 
> Hi,
> 	Is there anything special I need to know about VP3's 
> IDCT? I mean
> besides the fact that there are separate IDCTs to handle sparse
> coefficient matrices. Are the IDCT functions mathematically 
> equivalent to
> any textbook IDCT functions?
> 
> 	Thanks...
> --
> 	-Mike Melanson
> 
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