DCT-Quantum-Matrix-Generator-C++

DCT_QMG.cpp

#include "DCT_QMG.hpp"

// Quantitum Matrix: Q_{50}
// using Q_{50} as a standard to generate other Matrix
std::vector<double> DCT::Quant_matrix_50 = std::vector<double> {
        16, 11, 10, 16, 24, 40, 51, 61,
        12, 12, 14, 19, 26, 58, 60, 55,
        14, 13, 16, 24, 40, 57, 69, 56,
        14, 17, 22, 29, 51, 87, 80, 62,
        18, 22, 37, 56, 68, 109,103,77,
        24, 35, 55, 64, 81, 104,113,92,
        49, 64, 78, 87, 103,121,120,101,
        72, 92, 95, 98, 112,100,103,99
};

/*
 * the function comes from the highest reply post in:
 * https://stackoverflow.com/questions/29215879/how-can-i-generalize-the-quantization-matrix-in-jpeg-compression
 *
 * through test(test_Q_gen),
 * this function can generate Q Matrix(e.g. Q_{10} and Q_{90}).
 */
std::vector<double> DCT::Quant_matrix_gen(size_t target_Q) {
    size_t S;
    if (target_Q < 50)
        S = 5000 / target_Q;
    else
        S = 200 - 2*target_Q;

    std::vector<double> ret;
    for (double elem : DCT::Quant_matrix_50) {
        size_t input = floor((S*elem + 50) / 100);
        ret.push_back(DCT::round(input));
    }
    return ret;
}

/*
 * round function
 * unsign is true:
 *  input is restricted in [0, 255]
 * while unsign is false:
 *  round() is round() in mathematic.
 */
int DCT::round(double input, bool unsign) {
    if (unsign) {
        if (input > 255)
            return 255;
        else if (input < 0)
            return 0;
        else
            return int(input + 0.5);
    }
    else {
        if (input > 0)
            return int(input + 0.5);
        else
            return int(input - 0.5);
    }
}

DCT_QMG.hpp

#include <vector>

namespace DCT {
    extern std::vector<double> Quant_matrix_50;
    std::vector<double> Quant_matrix_gen(
        size_t target_Q
    );
    int round(double input, bool unsign=1);
}