id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
1542	QPA algorithm does not work properly when internal bitdepth is 8	JaviCru		"When you enable the QPA algorithm (Perceptually optimised QP adaptation, `-qpa 1 --SliceChromaQPOffsetPeriodicity=1`) is enabled and the internal bit-depth parameter is the default set in the main .cfg files (`--internal-bitdepth=10`), the result is as expected, a considerable rate saving and an improvement in perceptual quality.

However, if we force the internal bitdepth to be 8 (`--internal-bitdepth=8`), the result is a considerable increase in bitrate compared to not enabling the QPA algorithm.

As an example, I have encoded frames 1, 101, 201, 301, 401 and 501 of the BQTerrace sequence in All Intra mode, with base QPs 22, 27, 32, 37 and 42. Here are the average results:

InternalBitDepth=8, QPA off

  ||= base QP =||= Mbps =||= MS-SSIM =||
  ||= 22 =|| 2.659 || 0.996 ||
  ||= 27 =|| 0.989 || 0.986 ||
  ||= 32 =|| 0.503 || 0.979 ||
  ||= 37 =|| 0.268 || 0.966 ||
  ||= 42 =|| 0.138 || 0.942 ||

InternalBitDepth=10, QPA off

  ||= base QP =||= Mbps =||= MS-SSIM =||
  ||= 22 =|| 2.724 || 0.996 ||
  ||= 27 =|| 1.021 || 0.987 ||
  ||= 32 =|| 0.517 || 0.979 ||
  ||= 37 =|| 0.275 || 0.967 ||
  ||= 42 =|| 0.142 || 0.944 ||

InternalBitDepth=8, QPA on

  ||= base QP =||= Mbps =||= MS-SSIM =||
  ||= 22 =|| 3.388 || 0.998 ||
  ||= 27 =|| 1.561 || 0.992 ||
  ||= 32 =|| 0.601 || 0.983 ||
  ||= 37 =|| 0.309 || 0.972 ||
  ||= 42 =|| 0.167 || 0.952 ||

InternalBitDepth=10, QPA on

  ||= base QP =||= Mbps =||= MS-SSIM =||
  ||= 22 =|| 2.454 || 0.996 ||
  ||= 27 =|| 0.820 || 0.986 ||
  ||= 32 =|| 0.408 || 0.977 ||
  ||= 37 =|| 0.210 || 0.963 ||
  ||= 42 =|| 0.115 || 0.935 ||

As can be seen, for a base QP of 22, enabling the QPA algorithm increases the bit rate by almost 1 Mbps if we compare the bit depth level of 8 versus 10, when it would be expected to have a very similar value.

I attach the RD curves corresponding to the tables, where you can visually appreciate the mentioned rate increase.

I suspect that the problem, if any, may be in the calculation of picture or block energy (activity), or in the algorithm that modifies the Lagrangian during the rate control."	defect	closed	minor	VTM-16.1	VTM	VTM-15.0	fixed	QPA, internal-bitdepth	ksuehring XiangLi fbossen jvet@…