LunaTranslator/cpp/winsharedutils/otsu.cpp

typedef struct
{
    BYTE b;
    BYTE g;
    BYTE r;
} RGB;

int calculateOtsuThreshold(const std::vector<uint8_t> &grayscaleImage)
{
    int histogram[256] = {0};
    int totalPixels = grayscaleImage.size();

    for (int i = 0; i < totalPixels; ++i)
    {
        histogram[grayscaleImage[i]]++;
    }

    float maxVariance = 0.0f;
    int threshold = 0;

    for (int t = 0; t < 256; ++t)
    {
        int w0 = 0;
        int w1 = 0;
        int sum0 = 0;
        int sum1 = 0;

        for (int i = 0; i < 256; ++i)
        {
            if (i <= t)
            {
                w0 += histogram[i];
                sum0 += i * histogram[i];
            }
            else
            {
                w1 += histogram[i];
                sum1 += i * histogram[i];
            }
        }

        float mean0 = (w0 == 0) ? 0 : static_cast<float>(sum0) / w0;
        float mean1 = (w1 == 0) ? 0 : static_cast<float>(sum1) / w1;

        float variance = static_cast<float>(w0 * w1) * pow(mean0 - mean1, 2);
        if (variance > maxVariance)
        {
            maxVariance = variance;
            threshold = t;
        }
    }

    return threshold;
}
DECLARE_API bool otsu_binary(const void *image, int thresh)
{
    auto imageptr = (uintptr_t)image;
    BITMAPFILEHEADER *fileHeader = (BITMAPFILEHEADER *)imageptr;
    imageptr += sizeof(BITMAPFILEHEADER);
    BITMAPINFOHEADER *infoHeader = (BITMAPINFOHEADER *)imageptr;
    imageptr += sizeof(BITMAPINFOHEADER);

    int height, weight;
    height = infoHeader->biHeight;
    weight = infoHeader->biWidth;
    if (infoHeader->biBitCount == 24)
    {
        int size = height * weight;
        RGB *img = (RGB *)imageptr;
        int threshold;
        if (thresh == -1)
        {
            std::vector<uint8_t> grayscaleImage;

            for (int i = 0; i < size; i++)
            {
                grayscaleImage.push_back((BYTE)((img[i].r * 19595 + img[i].g * 38469 + img[i].b * 7472) >> 16));
            }
            threshold = calculateOtsuThreshold(grayscaleImage);
        }
        else
        {
            threshold = thresh;
        }
        for (int i = 0; i < size; i++)
        {
            if ((BYTE)((img[i].r * 19595 + img[i].g * 38469 + img[i].b * 7472) >> 16) > threshold)
            {
                img[i].r = img[i].g = img[i].b = 255;
            }
            else
            {
                img[i].r = img[i].g = img[i].b = 0;
            }
        }

        return true;
    }
    else
    {
        return false;
    }
}