[XviD-devel] lambda patch

Radek Czyz radoslaw at syskin.cjb.net
Fri Dec 9 06:12:34 CET 2005


I committed the small patch to HEAD and 1_0_branch, and tagged the two 
files as release_1_1_0. Hopefully I did this correctly, I was mostly 
guessing what I need to do ;))

I also committed the "expose VHQ and trellis lambda to plugins" patch 
(to HEAD), with one modification over what I shown you before (there was 
an xvidcore bug that was harmless until now). The patch is a NOP if no 
lambda plugins are connected.


Michael Militzer wrote:
> Hi Radek,
> indeed, it's a short patch ;) I have no objections against it: it's 
> reasonable to give a higher penalty to 8x8 modes, especially at VHQ=0.
> Also, I have no problem with switching back to a pure linear lambda
> scaling also for the low quants. As said, it won't make much of a 
> difference either way.
> As a side note: I've also ran some tests recently because of the lambdas.
> However, aside from 8x8/16x16 mode decision it also seemed to me that
> inter/intra decision isn't working perfectly with VHQ=0. On some sequences
> I had large gains from lowering the value of MV16_INTER_BIAS, e.g. to 400.
> You may want to give it a try if it works for your test sequences too...
> Regards,
> Michael
> Quoting Radek Czyz <radoslaw at syskin.cjb.net>:
>> Hi everyone,
>> I finally found some time to tweak lambdas and mode decisions back.
>> Effect:
>> - slowdown introduced by Michael's patch remains, but is now translated 
>> to PSNR gain at all quants, so it's worth it.
>> - I changed lambdas to be linear for low quants too. I understand 
>> Michael's reasoning for lower-than-psnr-best values (and probably agree 
>> with the theory). However, I believe that such HVS experiments belong to 
>> 1.2.-127 tree, and need some testing. With linear quants everywhere, at 
>> least we can explain slowdown as PSNR-boosting.
>> - I tweaked constants for much better VHQ 0 mode decision.
>> Patch is short, I put it online at http://syskin.is.dreaming.org/lambda.txt
>> I strongly think this is the best thing to do for 1.1.0, and the best 
>> starting point for 1.2.-127.
>> Comments? If no one writes anything (why that crossed my mind? lol) I'll 
>> commit to both cvs head and 1.1.0. If you disagree, say so now.
>> Regards,
>> Radek
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