JVET-AF0142 [AHG9] Local Film Grain Synthesis using Annotated Regions SEI [G. Teniou, S. Wenger (Tencent)]
Film Grain Synthesis (aka FGS) is a tool aimed at maintaining the original film grain while preserving the encoding efficiency due to its random nature and complexity. While being used to maintain the artistic intent or to mitigate visual artefacts, film grain is not necessarily applicable to the entire picture. This contribution proposes to address the film grain synthesis applied locally on the picture by using the annotated regions as a mask.
It is proposed to define labels for enabling/disabling FGS in certain regions.
The proposal is to send an ASCII string as payload in the annotated regions SEI (without changing its syntax or semantics). A change is necessary in FGC, expressing that, if such a label is detected, the film grain synthasis should be performed on the region or not.
It was commented by several experts that this would not be supported by existing devices, and implementation-wise is an additional processing step. The typical use case would be full-frame synthesis of FG.
If the approach would be applied such that it is generated full frame and then using a mask in overlaying, it might by OK, according to one expert.
It was commented that by using content layering the same functionality could also be achieved in legacy devices.
On the other hand, legacy devices may ignore it, anyway.
It was commented that the SEI message might simplify the synthesis when the properties of the two regions are very different.
The proposal would require a change of an existing SEI message, and also introduces an uncommon relationship between two SEI messages, deviating from the original purpose of the annotated regions SEI. Furthermore, there are other ways of achieving this functionality which are more consistent and have even additional flexibility (content layering, alpha map as per subsequent contribution).
No action was taken on this.
JVET-AF0142 [AHG9] Local Film Grain Synthesis using Annotated Regions SEI [G. Teniou, S. Wenger (Tencent)]
See section 4.12.