lsc_polynomial.h

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2024, Ideas On Board
 *
 * Helper for radial polynomial used in lens shading correction.
 */
#pragma once

#include <algorithm>
#include <array>
#include <assert.h>
#include <cmath>

#include <libcamera/base/log.h>
#include <libcamera/base/span.h>

#include "libcamera/internal/yaml_parser.h"

namespace libcamera {

LOG_DECLARE_CATEGORY(LscPolynomial)

namespace ipa {

class LscPolynomial
{
public:
    LscPolynomial(double cx = 0.0, double cy = 0.0, double k0 = 0.0,
              double k1 = 0.0, double k2 = 0.0, double k3 = 0.0,
              double k4 = 0.0)
        : cx_(cx), cy_(cy), cnx_(0), cny_(0),
          coefficients_({ k0, k1, k2, k3, k4 })
    {
    }

    double sampleAtNormalizedPixelPos(double x, double y) const
    {
        double dx = x - cnx_;
        double dy = y - cny_;
        double r = sqrt(dx * dx + dy * dy);
        double res = 1.0;
        for (unsigned int i = 0; i < coefficients_.size(); i++) {
            res += coefficients_[i] * std::pow(r, (i + 1) * 2);
        }
        return res;
    }

    double getM() const
    {
        double cpx = imageSize_.width * cx_;
        double cpy = imageSize_.height * cy_;
        double mx = std::max(cpx, std::fabs(imageSize_.width - cpx));
        double my = std::max(cpy, std::fabs(imageSize_.height - cpy));

        return sqrt(mx * mx + my * my);
    }

    void setReferenceImageSize(const Size &size)
    {
        assert(!size.isNull());
        imageSize_ = size;

        /* Calculate normalized centers */
        double m = getM();
        cnx_ = (size.width * cx_) / m;
        cny_ = (size.height * cy_) / m;
    }

private:
    double cx_;
    double cy_;
    double cnx_;
    double cny_;
    std::array<double, 5> coefficients_;

    Size imageSize_;
};

} /* namespace ipa */

#ifndef __DOXYGEN__

template<>
struct YamlObject::Getter<ipa::LscPolynomial> {
    std::optional<ipa::LscPolynomial> get(const YamlObject &obj) const
    {
        std::optional<double> cx = obj["cx"].get<double>();
        std::optional<double> cy = obj["cy"].get<double>();
        std::optional<double> k0 = obj["k0"].get<double>();
        std::optional<double> k1 = obj["k1"].get<double>();
        std::optional<double> k2 = obj["k2"].get<double>();
        std::optional<double> k3 = obj["k3"].get<double>();
        std::optional<double> k4 = obj["k4"].get<double>();

        if (!(cx && cy && k0 && k1 && k2 && k3 && k4))
            LOG(LscPolynomial, Error)
                << "Polynomial is missing a parameter";

        return ipa::LscPolynomial(*cx, *cy, *k0, *k1, *k2, *k3, *k4);
    }
};

#endif

} /* namespace libcamera */