[libcamera-devel] softISP for libcamera

[Hans de Goede]

Hi All,

I have pushed a new version of my optimization work here:

https://gitlab.freedesktop.org/camera/libcamera-softisp/-/commits/SoftwareISP-v02-hans1/

As the branch name suggests this has been rebased on top
of the SoftwareISP-v02 branch.

There are 2 new things here:

1. The color gains for whitebalance now use a lookup table
instead of a fixed 0-256 multiplication factor. This allows
color gains > 1.0 without needing to call std::min() 6 million
times per frame (for FHD) to clamp. Gains > 1.0 are is necessary
to avoid overexposed white areas like a lamp on the ceiling
or a window in the roof to not turn purple.

At least in my measurements the lookups are actually
a bit faster then the multiplication + fixed divide by 256
used before.

And on top of this using lookup tables allows adding
gamma correction for free. So I have added gamma correction
now too.

Together this results in a pretty usable picture.
My home-office has pretty bad lighting conditions at night
and here is what the official proprietary Intel stack
generates as image:

https://fedorapeople.org/~jwrdegoede/ov2740-intel-stack.png

And here is the softisp code with fixed white-balance
and gamma-correction:

https://fedorapeople.org/~jwrdegoede/ov2740-softisp.png

This is with manually tweaked vertical blank time
to drop the FPS to exactly 25 fps so that it is
synced with the artificial light frequency, to avoid
the typical banding sometimes seen with artificial
lightning. I think we will need some way to control
this to libcamera. Does libcamera already have a way
for an app to request light-frequency filtering ?

I see on my main monitor that this looks a bit
overexposed. Which is interesting because it looked
less overexposed on the actual laptop ...

My plan for tomorrow / next week is to write
a debayer-class. I plan to add the debayer-class
as a separate commit which just adds it and
then port the softisp code over to it in
a separate commit. The idea being that the next
version of this series can then just cherry-pick
the patch adding the debayering class as is and
then integrate / squash the changes to move
the softisp code over to the separate class.

Regards,

Hans