C++实现Floyd-Steinberg错误扩散图像减色功能异常排查

我尝试实现Floyd-Steinberg错误扩散算法，当前函数支持无错误扩散的图像减色（减至8色），该功能运行正常，但开启错误扩散后，彩色图像处理效果异常，仅灰度图像表现正常。以下是实现代码及不同处理方式的效果对比：

#define BYTE_BOUND(value) (value > 255 ? 255 : (value < 0 ? 0 : value))

Image& Image::color_reduce(bool error_diffusion) {
    double r_diff, g_diff, b_diff, a[] = {0, 0, 0};
    std::pair<double, double*> min(INFINITY, a);
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            min.first = INFINITY;
            for (int color = 0; color < 8; color++) {
                r_diff = data[(i * w + j) * channels] - (((1 << 2) & color) ? 255 : 0);
                g_diff = data[(i * w + j) * channels + (uint8_t)fmin(1, channels - 1)] - (((1 << 1) & color) ? 255 : 0);
                b_diff = data[(i * w + j) * channels + (uint8_t)fmin(2, channels - 1)] - ((1 & color) ? 255 : 0);
                if (r_diff * r_diff + g_diff * g_diff + b_diff * b_diff < min.first) {
                    min.first = r_diff * r_diff + g_diff * g_diff + b_diff * b_diff;
                    min.second[0] = r_diff;
                    min.second[1] = g_diff;
                    min.second[2] = b_diff;
                }
            }
            data[(i * w + j) * channels] -= min.second[0];
            data[(i * w + j) * channels + (uint8_t)fmin(1, channels - 1)] -= min.second[1];
            data[(i * w + j) * channels + (uint8_t)fmin(2, channels - 1)] -= min.second[2];
            if (error_diffusion) {
                // Floyd-Steinberg Error Diffusion
                for (int c_cn = 0; c_cn < (int) fmin(3, channels); c_cn++) {

                    data[(i * w + (uint32_t)fmin(j + 1, w - 1)) * channels + c_cn] =
                        (uint8_t) BYTE_BOUND(data[(i * w + (uint32_t)fmin(j + 1, w - 1)) * channels] + 7/16.0 * min.second[c_cn]);

                    data[((uint32_t)fmin(i + 1, h - 1) * w + (uint32_t)fmin(j + 1, w - 1)) * channels + c_cn] =
                        (uint8_t) BYTE_BOUND( data[((uint32_t)fmin(i + 1, h - 1) * w + (uint32_t)fmin(j + 1, w - 1)) * channels + c_cn] + 1/16.0 * min.second[c_cn]);

                    data[((uint32_t)fmin(i + 1, h - 1) * w + j) * channels + c_cn] =
                        (uint8_t) BYTE_BOUND(data[((uint32_t)fmin(i + 1, h - 1) * w + j) * channels + c_cn] + 5/16.0 * min.second[c_cn]);

                    data[((uint32_t)fmin(i + 1, h - 1) * w + (uint32_t)fmax(j - 1, 0)) * channels + c_cn] =
                        (uint8_t) BYTE_BOUND(data[((uint32_t)fmin(i + 1, h - 1) * w + (uint32_t)fmax(j - 1, 0)) * channels + c_cn] + 3/16.0 * min.second[c_cn]); 
                }
            }
        }
    }
    return *this;
}

效果对比 #

• 原图
  
• 无错误扩散的减色效果
  
• 开启错误扩散的减色效果
  
• 灰度图处理效果（正常）
  

内容的提问来源于stack exchange，提问作者Zero G