opencv::调整图像亮度与对比度

图像变换可以看作如下：
 - 像素变换 – 点操作
 - 邻域操作 – 区域

调整图像亮度和对比度属于像素变换-点操作

//创建一张跟原图像大小和类型一致的空白图像、像素值初始化为0
Mat new_image = Mat::zeros( image.size(), image.type() );  

//确保值大小范围为0~255之间
saturate_cast<uchar>(value)

//给每个像素点每个通道赋值
Mat.at<Vec3b>(y,x)[index]=value 

int main(int argc, char** argv) {

    Mat src, dst;
    src = imread(STRPAHT2);
    if (!src.data) {
        printf("could not load image...
");
        return -1;
    }
    char input_win[] = "input image";
    cvtColor(src, src, CV_RGB2GRAY);
    namedWindow(input_win, CV_WINDOW_AUTOSIZE);
    imshow(input_win, src);

    int height = src.rows;
    int width = src.cols;
    //创建一张跟原图像大小和类型一致的空白图像、像素值初始化为0
    dst = Mat::zeros(src.size(), src.type());
    float alpha = 1.2;
    float beta = 30;

    Mat m1;
    src.convertTo(m1, CV_32F);
    for (int row = 0; row < height; row++) {
        for (int col = 0; col < width; col++) {
            if (src.channels() == 3) {
                float b = m1.at<Vec3f>(row, col)[0];// blue
                float g = m1.at<Vec3f>(row, col)[1]; // green
                float r = m1.at<Vec3f>(row, col)[2]; // red

                // output
                dst.at<Vec3b>(row, col)[0] = saturate_cast<uchar>(b*alpha + beta);
                dst.at<Vec3b>(row, col)[1] = saturate_cast<uchar>(g*alpha + beta);
                dst.at<Vec3b>(row, col)[2] = saturate_cast<uchar>(r*alpha + beta);
            }
            else if (src.channels() == 1) {
                float v = src.at<uchar>(row, col);
                dst.at<uchar>(row, col) = saturate_cast<uchar>(v*alpha + beta);
            }
        }
    }

    char output_title[] = "contrast and brightness change demo";
    namedWindow(output_title, CV_WINDOW_AUTOSIZE);
    imshow(output_title, dst);

    waitKey(0);
    return 0;
}