View Single Post
Old 26th May 2003, 18:57   #20  |  Link
Acaila
Retired
 
Acaila's Avatar
 
Join Date: Jan 2002
Location: Netherlands
Posts: 1,529
Quote:
This leads me to conclude that, since Qpel works with smaller motions than Hpel, Qpel will be less efficient when using high QM values, because the effect of Qpel will be nullified by the high thresholds of the QM. The minimum use of bits by Qpel will remain the same tho.
Am I right in this?
I don't know why you brought QPel into this, for it has next to nothing to do with quantization. QPel increases the sensitivity of Motion Estimation. Once that process is finished the motion estimated frame is subtracted from the current frame with the result being a residual frame. It in on this residual frame that quantization is applied. QPel works before QM, and so there's no way that high QM could nullify the effect of QPel (more like the other way around if anything).
QPel helps to catch more motion, so it decreases the size of the residual frame, and thus also decreases the amount of effect of the QM. If ME were to work for 100% the residual frame would be empty and no quantization (of the residual frame anyway) could take place.

Quote:
3-Using high values for high frequencies in B/P-frame QM could improve compressability.
And that's exactly what all matrices already do...
And since using too high values cause ringing as mentioned before, I believe the standard matrices are already quite well made. The only reason I could see anyone using a custom QM is for increasing the amount of detail/size of a video (since for higher compression you could just as well use a higher quant, no need for a custom matrix).

Quote:
Also, does anybody have the QM's for DivX 3 Low-motion and Fast-motion?
As far as I know the two flavors of DivX 3 have identical quantization matrices. The only difference is the quant ranges that they can use. I believe low-motion could use anything 2-31, while the high-motion codec could only use 4-31, but I'm not sure if these ranges are correct.

Last edited by Acaila; 26th May 2003 at 19:06.
Acaila is offline   Reply With Quote