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Didée · 15th December 2002, 13:32

I did no serious compares/researches on the qpel feature lately. Furthermore, I am speaking out of pure theory now, but anyway:

In principle, qpel should deliver better compressability, because the ME can "point" more precisly on the destination block, and thus lower quants are needed, resp. the compression gets better for a given quant.
The problem is (was), that with activated qpel the search distance is cut to half, and therefore the ME might not find the best possible destination block. This must obviously lead to worse compressability in mid/hi-motion scenes.
Now, this problem should have become minor since XviD has dynamic qpel decision in the latest alphas: using qpel on lo motion, and take the benefit. On mid/hi motion, take classic hpel to catch the motion better.

If the above is not right, *please* do correct me!
I'm not into the codec's inner mysteries (as you might see from my probably not-quite-right terminology above) ... but in general, I like theoretic approaches, and I (would) like to understand how things are really working!

Regards and Thx

Didée

15th December 2002, 13:32	#12 \| Link
Didée Registered User Join Date: Apr 2002 Location: Germany Posts: 5,391	I did no serious compares/researches on the qpel feature lately. Furthermore, I am speaking out of pure theory now, but anyway: In principle, qpel should deliver better compressability, because the ME can "point" more precisly on the destination block, and thus lower quants are needed, resp. the compression gets better for a given quant. The problem is (was), that with activated qpel the search distance is cut to half, and therefore the ME might not find the best possible destination block. This must obviously lead to worse compressability in mid/hi-motion scenes. Now, this problem should have become minor since XviD has dynamic qpel decision in the latest alphas: using qpel on lo motion, and take the benefit. On mid/hi motion, take classic hpel to catch the motion better. If the above is not right, please do correct me! I'm not into the codec's inner mysteries (as you might see from my probably not-quite-right terminology above) ... but in general, I like theoretic approaches, and I (would) like to understand how things are really working! Regards and Thx Didée __________________ - We´re at the beginning of the end of mankind´s childhood - My little flickr gallery. (Yes indeed, I do have hobbies other than digital video!)