[PATCH 00/10] Centralise Agc into libipa

[Daniel Scally]

Hello all

The IPU3 and RkISP1 IPAs do Agc the same way (following the Rpi method closely),
but the implementations are wholly separate. This introduces the potential for
divergence and also makes both maintenance and improvement more difficult. This
series unifies them as derivations of a new MeanLuminanceAgc class within
libipa. The algorithm itself is done through functions of the base class
with the IPA's derived classes providing a function through which the mean
luminance input to the algorithm can be calculated from their specific stats
formats.

The old implementations effectively hard coded values for the AeConstraintMode
and AeExposureMode controls; they adhered to a single lower-bound constraint of
0.5 across the top 2% of a Histogram and acted as though the AeExposureMode
expected shutter time to be driven to its maximum before touching gain at all.
The base class additionally adds infrastructure to discover the supported values
for AeConstraintMode and AeExposureMode controls from a camera sensor tuning
file and uses the values defined in those files with the algorithm instead,
though as no tuning files are modified in this series the behaviour currently
remains as it was before.

The series **does** alter the calculated shutter time and gain for both the
IPU3 and RkISP1 compared to their bespoke implementations, for two reasons:

1. A bug in the way they were implemented meant that an over-exposed image was
   corrected more slowly than an under-exposed one. This is fixed and will
   improve both IPAs' response to a too-bright image.
2. The default kRelativeLuminanceTarget is centrally set to 0.16 which matches
   the value from the IPU3 implementation. In the RkISP1 implementation that
   value was set to 0.4 with a \todo to see why they were different. My belief
   is that they were different because they were implemented in different
   lighting conditions. In my very imperfect testing setup the 0.16 target
   produced reasonable images on both.

Without those two changes, the shutter time and gain calculated after this
series matches those calculated by their independent implementations.

Thanks
Dan

Daniel Scally (9):
  ipa: libipa: Allow creation of empty Histogram
  libcamera: controls: Generate enum value-name maps
  ipa: libipa: Add MeanLuminanceAgc base class
  ipa: ipu3: Parse and store Agc stats
  ipa: ipu3: Derive ipu3::algorithms::Agc from MeanLuminanceAgc
  ipa: ipu3: Remove bespoke AGC functions from IPU3
  ipa: rkisp1: Add parseStatistics() to Agc
  ipa: rkisp1: Derive rkisp1::algorithms::Agc from MeanLuminanceAgc
  ipa: rkisp1: Remove bespoke Agc functions

Paul Elder (1):
  ipa: libipa: Add ExposureModeHelper

 include/libcamera/control_ids.h.in      |   2 +
 include/libcamera/property_ids.h.in     |   2 +
 src/ipa/ipu3/algorithms/agc.cpp         | 306 ++++----------
 src/ipa/ipu3/algorithms/agc.h           |  27 +-
 src/ipa/ipu3/ipa_context.cpp            |   3 +
 src/ipa/ipu3/ipa_context.h              |   5 +
 src/ipa/ipu3/ipu3.cpp                   |   2 +-
 src/ipa/libipa/agc.cpp                  | 526 ++++++++++++++++++++++++
 src/ipa/libipa/agc.h                    |  82 ++++
 src/ipa/libipa/exposure_mode_helper.cpp | 307 ++++++++++++++
 src/ipa/libipa/exposure_mode_helper.h   |  61 +++
 src/ipa/libipa/histogram.h              |   1 +
 src/ipa/libipa/meson.build              |   4 +
 src/ipa/rkisp1/algorithms/agc.cpp       | 303 ++++----------
 src/ipa/rkisp1/algorithms/agc.h         |  19 +-
 src/ipa/rkisp1/ipa_context.h            |   5 +
 src/ipa/rkisp1/rkisp1.cpp               |   2 +-
 utils/gen-controls.py                   |  19 +
 18 files changed, 1219 insertions(+), 457 deletions(-)
 create mode 100644 src/ipa/libipa/agc.cpp
 create mode 100644 src/ipa/libipa/agc.h
 create mode 100644 src/ipa/libipa/exposure_mode_helper.cpp
 create mode 100644 src/ipa/libipa/exposure_mode_helper.h

-- 
2.34.1