DiscreteCosineTransform.cpp

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#include "DiscreteCosineTransform.h"
 
//=====================================================================================
krotos::DiscreteCosineTransform::DiscreteCosineTransform() : m_inputSize(40), m_outputSize(13)
{
    buildDctMatrix(m_inputSize, m_outputSize);
}
 
void krotos::DiscreteCosineTransform::setInputOutputSize(const std::size_t& inputSize, const std::size_t& outputSize)
{
    buildDctMatrix(inputSize, outputSize);
}
 
//=====================================================================================
std::vector<float> krotos::DiscreteCosineTransform::calculateDCT(const std::vector<float>& input)
{
 
    if (input.size() != m_inputSize)
    {
        buildDctMatrix(input.size(), m_outputSize);
    }
 
    std::vector<float> result(m_outputSize, 0.f);
    for (int i = 0; i < m_outputSize; ++i)
    {
        for (int j = 0; j < m_inputSize; ++j)
        {
            result[i] += input[j] * m_dctMatrix[i][j];
        }
    }
 
    return result;
}
 
void krotos::DiscreteCosineTransform::buildDctMatrix(const std::size_t& inputSize, const std::size_t& outputSize)
{
    m_inputSize = inputSize;
    m_outputSize = outputSize;
 
    m_dctMatrix.resize(m_outputSize, std::vector<float>(m_inputSize, 0.f));
 
    // scale for index = 0
    auto scale0 = 1.0f / std::sqrt(m_inputSize);
 
    // scale for index != 0
    auto scale1 = std::sqrt(2.0f / m_inputSize);
 
    for (int i = 0; i < m_outputSize; ++i)
    {
        auto scale = (i == 0) ? scale0 : scale1;
        auto k = m_pi / m_inputSize * i;
        for (int j = 0; j < m_inputSize; ++j)
        {
            m_dctMatrix[i][j] = static_cast<float>(scale * std::cos(k * (j + 0.5)));
        }
    }
}