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Old 2nd August 2018, 11:48   #1  |  Link
iAvoe
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Join Date: Sep 2017
Posts: 9
In HEVC, only QP=4 is truly lossless quantization... what about 0~3?

This is definitly very hard to answer, the document source: x265.readthedocs.io/en/default/lossless.html

Updated - Aug.16:
Quantization is the process of dividing the DCT coefficients by another matrix that is sorted by quantizer, when specifed QP=0, x265 skips dividing and gives output. When QP=4, x265 gives a lossless output that is same as x264's QP=0.

Since value 0~3 are available, and 0 disables quantization, it appears the --qp option has 4 states:
0 disable, 1~3 unknown, 4 lossless and 5~51 x264Setting+4

I thought this could be an error in the doc, but they also says the highest RDO optmization is --qp 4, which it's lossless.
Since 4 is --qp 0 in x264, it looks like we need to give a +-4 to switch encoders, but it won't make sense when the maximum of --qp is 51.

Last edited by iAvoe; 16th August 2018 at 06:24. Reason: make my sentences readable
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