[PATCH v2 2/3] ipa: libipa: Add MatrixInterpolator class

[Stefan Klug]

Hi Paul,

thanks for the patch.

On Fri, Apr 19, 2024 at 04:18:18PM +0900, Paul Elder wrote:
> Add a class to encapsulate the functionality of fetching a matrix based
> on an integer key, and interpolating if there is no exact match. This is
> expected to be used by both color correction matrices / crosstalk
> correction as well as lens shading correction.
> 
> Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
> 
> ---
> Changes in v2:
> - initialize to identity matrix
> - add a function to reset to identity matrix
> - other minor fixes
> ---
>  src/ipa/libipa/matrix_interpolator.cpp |  54 +++++++++++++
>  src/ipa/libipa/matrix_interpolator.h   | 105 +++++++++++++++++++++++++
>  src/ipa/libipa/meson.build             |   2 +
>  3 files changed, 161 insertions(+)
>  create mode 100644 src/ipa/libipa/matrix_interpolator.cpp
>  create mode 100644 src/ipa/libipa/matrix_interpolator.h
> 
> diff --git a/src/ipa/libipa/matrix_interpolator.cpp b/src/ipa/libipa/matrix_interpolator.cpp
> new file mode 100644
> index 00000000..fc1837e7
> --- /dev/null
> +++ b/src/ipa/libipa/matrix_interpolator.cpp
> @@ -0,0 +1,54 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2019, Raspberry Pi Ltd
> + * Copyright (C) 2024, Paul Elder <paul.elder at ideasonboard.com>
> + *
> + * matrix_interpolator.cpp - Helper class for interpolating maps of matrices
> + */
> +#include "matrix_interpolator.h"
> +
> +#include <algorithm>
> +#include <string>
> +
> +#include <libcamera/base/log.h>
> +
> +#include "libcamera/internal/yaml_parser.h"
> +
> +#include "matrix.h"
> +
> +/**
> + * \file ccm.h
> + * \brief Helper class for interpolating maps of matrices
> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(MatrixInterpolator)
> +
> +namespace ipa {
> +
> +/**
> + * \class MatrixInterpolator
> + * \brief Class for storing, retrieving, and interpolating matrices
> + */
> +
> +/**
> + * \fn int MatrixInterpolator<T, R, C>::readYaml(const libcamera::YamlObject &yaml)
> + * \brief Initialize an MatrixInterpolator instance from yaml
> + * \tparam T Type of data stored in the matrices
> + * \tparam R Number of rows of the matrices
> + * \tparam C Number of columns of the matrices
> + * \param[in] yaml The yaml object that contains the map of unsigned integers to matrices
> + * \return Zero on success, negative error code otherwise
> + */
> +
> +/**
> + * \fn Matrix<T, R, C> MatrixInterpolator<T, R, C>::get(unsigned int key)
> + * \brief Retrieve a matrix from the list of matrices, interpolating if necessary
> + * \param[in] key The unsigned integer key of the matrix to retrieve
> + * \return The matrix corresponding to the color temperature
> + */
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> diff --git a/src/ipa/libipa/matrix_interpolator.h b/src/ipa/libipa/matrix_interpolator.h
> new file mode 100644
> index 00000000..ddc7b350
> --- /dev/null
> +++ b/src/ipa/libipa/matrix_interpolator.h
> @@ -0,0 +1,105 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2019, Raspberry Pi Ltd
> + * Copyright (C) 2024, Paul Elder <paul.elder at ideasonboard.com>
> + *
> + * matrix_interpolator.h - Helper class for interpolating maps of matrices
> + */
> +
> +#pragma once
> +
> +#include <algorithm>
> +#include <map>
> +#include <string>
> +#include <tuple>
> +
> +#include <libcamera/base/log.h>
> +
> +#include "libcamera/internal/yaml_parser.h"
> +
> +#include "matrix.h"
> +
> +namespace libcamera {
> +
> +LOG_DECLARE_CATEGORY(MatrixInterpolator)
> +
> +namespace ipa {
> +
> +template<typename T, unsigned int R, unsigned int C,
> +	 std::enable_if_t<std::is_arithmetic_v<T>> * = nullptr>
> +class MatrixInterpolator
> +{
> +public:
> +	MatrixInterpolator()
> +	{
> +		reset();
> +	};
> +
> +	~MatrixInterpolator(){};
> +
> +	void reset()
> +	{
> +		Matrix<T, R, C> unit;
> +		matrices_[0] = unit;

I thinks that stems from a my bad english :-) As Kieran wrote in another
mail it should be called "identity".

I wonder however if reset should actually add a matrix. It makes
readYaml more complicated and would be easy to catch in get().

> +	}
> +
> +	int readYaml(const libcamera::YamlObject &yaml)
> +	{
> +		int ret;

Here matrices must be erased. Otherwise he one from reset is still in
there (or the ones from a previous readYaml).

> +
> +		if (!yaml.isDictionary()) {
> +			LOG(MatrixInterpolator, Error) << "yaml object must be a dictionary";
> +			return -EINVAL;
> +		}
> +
> +		for (const auto &[ctStr, value] : yaml.asDict()) {
> +			unsigned int ct = std::stoul(ctStr);
> +			Matrix<T, R, C> matrix;
> +			if ((ret = matrix.readYaml(value)) < 0) {
> +				LOG(MatrixInterpolator, Error) << "Failed to read matrix";
> +				return ret;
> +			}
> +
> +			matrices_[ct] = matrix;
> +
> +			LOG(MatrixInterpolator, Debug)
> +				<< "Read matrix for key " << ct << ": "
> +				<< matrices_[ct].toString();
> +		}
> +
> +		if (matrices_.size() < 1) {
> +			LOG(MatrixInterpolator, Error) << "Need at least one matrix";
> +			return -EINVAL;
> +		}
> +
> +		return 0;
> +	}
> +
> +	Matrix<T, R, C> get(unsigned int ct)
> +	{

I think a check for matrices_.size() == 0 wouldn't hurt here. Or even
better a assert, as there is no way to continue in a sensible way.

Regards,
Stefan

> +		if (matrices_.size() == 1 ||
> +		    ct <= matrices_.begin()->first)
> +			return matrices_.begin()->second;
> +
> +		if (ct >= matrices_.rbegin()->first)
> +			return matrices_.rbegin()->second;
> +
> +		if (matrices_.count(ct))
> +			return matrices_[ct];
> +
> +		/* The above four guarantee that this will succeed */
> +		auto iter = matrices_.upper_bound(ct);
> +		unsigned int ctUpper = iter->first;
> +		unsigned int ctLower = (--iter)->first;
> +
> +		double lambda = (ct - ctLower) / static_cast<double>(ctUpper - ctLower);
> +		return lambda * matrices_[ctUpper] + (1.0 - lambda) * matrices_[ctLower];
> +	}
> +
> +private:
> +	std::map<unsigned int, Matrix<T, R, C>> matrices_;
> +};
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
> index 1e34355f..305acf64 100644
> --- a/src/ipa/libipa/meson.build
> +++ b/src/ipa/libipa/meson.build
> @@ -8,6 +8,7 @@ libipa_headers = files([
>      'fc_queue.h',
>      'histogram.h',
>      'matrix.h',
> +    'matrix_interpolator.h',
>      'module.h',
>      'pwl.h',
>  ])
> @@ -20,6 +21,7 @@ libipa_sources = files([
>      'fc_queue.cpp',
>      'histogram.cpp',
>      'matrix.cpp',
> +    'matrix_interpolator.cpp',
>      'module.cpp',
>      'pwl.cpp'
>  ])
> -- 
> 2.39.2
>