[RFC/PATCH v1 0/8] Implement polynomial lsc loader

[Stefan Klug]

Hi all,

This series is not yet completely polished, as I'd like to get some
feedback on the overall direction first. It is based on my colour
temperature series [1].

Polynomial functions allow a relatively precise representation of the
lensshading. The formula used here is from the DNG specification [2]
page 110. Initial implementations in libtuning show that the overall
error is quite low, but it is not yet clear if the ability to model the
lens shading is sufficient for all cases.

The huge benefit of polynomials is that they can be easily resampled for
arbitrary crop rectangles. In case of the rkisp1 the hardware is
configured using a 17x17 grid of gains.  Resampling these for a
arbitrary crop rectangle on the sensor leads to a degradation in
quality. This can either be mitigated using a higher resolution grid as
basis or by describing the lens shading using polynomials. This series
implements the latter.

Patches 1-3 replace the matrix interpolator with a generic interpolator
class. This is only refactoring without functional changes.

Patch 4 Uses the new interpolator for the current lsc algorithm.

Patch 5-8 Implement a loader for polynomial lens shading coefficients.
Sampling for the current sensor crop rectangle is done at load time.

Questions I have in mind:
- libipa/polynomial.h is only used inside the loader. Is that worth a
  own file, or should it be defined in lsc.cpp?
- lsc.cpp now contains several helper classes on the top. Are these fine
  there, or should they be moved into another file?

I'm happy for any feedback.

Best regards,
Stefan

[1] https://patchwork.libcamera.org/project/libcamera/list/?series=4514
[1] https://helpx.adobe.com/content/dam/help/en/photoshop/pdf/DNG_Spec_1_7_1_0.pdf


Stefan Klug (8):
  ipa: libipa: Add generic Interpolator class
  ipa: rkisp1: Use generic Interpolator class
  ipa: rkisp1: Remove MatrixInterpolator
  ipa: rkisp1: Use interpolator in lsc
  ipa: rkisp1: Move loader functions into helper class
  ipa: libipa: Add lsc polynomial class
  ipa: rkisp1: Add sensor info to context
  ipa: rkisp1: Add polynomial LSC loader

 src/ipa/libipa/interpolator.cpp        | 139 +++++++++
 src/ipa/libipa/interpolator.h          | 139 +++++++++
 src/ipa/libipa/matrix_interpolator.cpp | 110 -------
 src/ipa/libipa/matrix_interpolator.h   | 122 --------
 src/ipa/libipa/meson.build             |   6 +-
 src/ipa/libipa/polynomial.cpp          |  23 ++
 src/ipa/libipa/polynomial.h            | 107 +++++++
 src/ipa/rkisp1/algorithms/awb.cpp      |   4 +-
 src/ipa/rkisp1/algorithms/awb.h        |   5 +-
 src/ipa/rkisp1/algorithms/ccm.cpp      |  18 +-
 src/ipa/rkisp1/algorithms/ccm.h        |   6 +-
 src/ipa/rkisp1/algorithms/lsc.cpp      | 405 +++++++++++++++----------
 src/ipa/rkisp1/algorithms/lsc.h        |  13 +-
 src/ipa/rkisp1/ipa_context.h           |   2 +
 src/ipa/rkisp1/rkisp1.cpp              |   4 +-
 15 files changed, 684 insertions(+), 419 deletions(-)
 create mode 100644 src/ipa/libipa/interpolator.cpp
 create mode 100644 src/ipa/libipa/interpolator.h
 delete mode 100644 src/ipa/libipa/matrix_interpolator.cpp
 delete mode 100644 src/ipa/libipa/matrix_interpolator.h
 create mode 100644 src/ipa/libipa/polynomial.cpp
 create mode 100644 src/ipa/libipa/polynomial.h

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2.43.0