[libcamera-devel] [RFC PATCH 0/2] libcamera: converter: introduce software converter for debayering and AWB

[Andrey Konovalov]

Here is a draft implementation of Bayer demosaicing which follows the
Converter interface and runs on CPU.

It also includes a naive version of Grey World AWB. Just for demo purposes
(to make the final image looking a bit nicer). Otherwise, Converter isn't
the right place for AWB - only the statistics should be gathered here,
and the rest belongs to an IPA module.

Currently this software converter supports single output only, but adding
the second stream for statistics is under consideration.

As libcamera::Converter currently assumes a media device underneath the
convertor, I wasn't able to avoid hacking the simple pipeline handler to make
it work with the software converter. For the same reason ConverterFactory
is not used for now.

Only RAW10P format from the sensor is currently supported, but adding more
Bayer formats wouldn't be a problem. Out of 10 bits, only 8 most significant
ones are used to lessen the load on CPU. Simple bilinear interpolation is
used for the same reason.

AWB simplifications:
- a naive implementation of "Grey World" algorithm: all pixels are used (no
  brightest and darkest pixels excluded from the calculations)
- to lessen the load on CPU, works on raw Bayer data and takes red values from
  red pixels, blue values from blue, and green values from green pixels only. 
- to lessen the load on CPU, the red/green/blue gains calculated from the
  current frame data are applied to the next frame. These gains are purely
  in software (no V4L2 controls are set).

No performance analysis or tuning have been done yet. On RB5 board this
software convertor gives:
  ~ 5 fps at 3278x2462 (camera sensor runs at 15 fps)
  ~ 18..19 fps at 1918x1078 (out of 30 fps)
  ~ 18..19 fps at 1638x1230 (out of 30 fps)
  ~ 30 fps at 638x478 (out of 30 fps)
(The resolutions above are the output ones; demosaic filter drops 1 pixel
from each side of the frame, so that 3280x2464 from the camera sensor becomes
3278x2462 etc)

Andrey Konovalov (2):
  libcamera: converter: add software converter
  [DNI] libcamera: pipeline: simple: a hack to use sotware converter
    with qcom-camss

 .../internal/converter/converter_softw.h      |  90 ++++
 src/libcamera/converter/converter_softw.cpp   | 430 ++++++++++++++++++
 src/libcamera/converter/meson.build           |   3 +-
 src/libcamera/pipeline/simple/simple.cpp      |  22 +-
 4 files changed, 542 insertions(+), 3 deletions(-)
 create mode 100644 include/libcamera/internal/converter/converter_softw.h
 create mode 100644 src/libcamera/converter/converter_softw.cpp

-- 
2.34.1