[Mp4-tech] RE: Regarding Hadamard in H264

[Gary Sullivan]

Gomathi Ramamoorthy et al,
The Hadamard transform is only applied to the DC coefficients of the 1st transform stage, and it is only applied under certain circumstances (chroma always, and luma for Intra_16x16 macroblocks).  This has an effect somewhat similar to the use of a larger transform block size and analogous to wavelet transform concepts (in wavelet transforms, there are fewer coefficients associated with lower frequencies than for higher frequencies, and the basis functions are longer for the lower-frequency components).
When signals predominantly contain low frequency phenomena, having longer basis functions (or larger blocks for a block transform) can improve compression.  When they predominantly contain non-stationary short localized phenomena, having shorter basis functions can provide a better ability to adapt to localized statistics and avoid "ringing" artifacts.  A hierarchical transform design like this one provides a sort of hybrid between these two approaches.
Some of the motivating issues here are perceptual-based as well as "objective".
Best Regards,
Gary Sullivan
________________________________
From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Gomathi Ramamoorthy
Sent: Tuesday, October 09, 2023 6:02 AM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] Regarding Hadamard in H264
Dear All,
Why do we use hadamard transform in h264 that too at the output of DCT coefficients.Since we have already taken DCT does it make sence if we again apply a transform to an already transformed set of coefficients.
Please clarify
Thanks & Regards,
Gomathi Ramamoorthy| Senior Engineer | Mindtree Consulting Ltd | Global Village , RVCE post , Mysore Road, Bangalore - 560059,India | Voice +91 80 26264000 Extn 66521 | Fax +91 80 26264100 | Mob +91 9901074757 | Email: gomathi_ramamoorthy mindtree.com<mailto:gomathi_ramamoorthy mindtree.com> | www.mindtree.com<http://www.mindtree.com/>|
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