JVET-F0038 AHG8: adaptive QP for 360° video coding [F. Racape, F. Galpin, G. Rath, E. François (Technicolor)]
This contribution presents the results of encoding ERP sequences with a vertically adapted QP. On HM-16.15, it was reported that this method brings, 4.3%, 2.9% coding gains in RA main 10, AI 1 frame main 10 configurations, w.r.t WS-PSNR. It is proposed to include such an adaptive QP when generating the anchors for an asserted more fair comparison between the different proposed projections.
This uses a similar formula for QP adaptation as used in WS-PSNR, therefore the improvement on that criterion is not surprising. The QP adaptation is signalled by the encoder.
Typically, this ends up in QP+12 from the equator to the poles (4× the quantization step size), clipped if the value 51 would be surpassed. Some experts raised a concern that this might be too aggressive.
No assessment of subjective effects had been done so far.
The proponents requested including this in the CTC, but more study seemed necessary.
If used for ERP, it should also be considered for other projection formats.