Pispconvert: Color bug / visual artefacts only present on C1

[jack-obrien]

Hi there, I have found a few visual bugs when doing color format conversions with pispconvert. These ones are only present on the C1 stepping of the BCM2712 SOC.

The bugs are:

1. Image too blue when output of pispconvert is NV12.
2. Image has vertical bar artefacts when output of pispconvert is BGRx or RGBx

Please refer to my forum post for more details. https://forums.raspberrypi.com/viewtopic.php?t=399760

Thanks!!

[njhollinghurst]

These are known limitations of ISP-BE minor version 0 in BCM2712C1:

1. insufficient bit-depth for colour matrix offsets, means that those parameters can overflow leading to wrong offset;
2. the BPP_32 flag is ignored, so outputs requiring it will be written as 24bpp with black bars between tiles.

There are some point workarounds in convert.cpp and in libcamera, and others are feasible, though it probably won't be possible to cover all combinations of conversion and scaling.

It may take a while to figure out what can be done...

Eventually, it might make sense to move the workarounds into some common code that can be called from both the standalone and gstreamer converters.