如何在Opencv中处理图像的特定部分 [英] How can I process a specific part of an Image in Opencv

问题描述

我使用copyMakeBorder在我的图片周围创建了一个100x100x100x100的边框。我想使用cvtColor只将图像的边缘内部的部分转换为灰色，所以边框保持bgr，我不想使用copyTo来复制图像边框内的东西，我会喜欢处理的图像到位。我看了所有的谷歌和没有具体的代码示例来做到这一点。我可以请别人提供代码示例。

I used copyMakeBorder to create a 100x100x100x100 border around my image. I would like to use cvtColor to convert only the part of the image that is inside the border to gray, so the border remains bgr, I don't want to have to use copyTo to copy something inside the border on the image, I would like to process the image in place. I looked all over google and there was no specific code example to do this. May I ask someone provide code example.

推荐答案

什么Ed.S建议是正确的 - 在opencv中，你不能从更大的图像并将其从rgb转换为灰度而不转换整个图像：

What Ed.S suggested is right - in opencv you cannot take some ROI from the bigger image and convert it in place from rgb to grayscale not converting whole image:

Mat src(1024, 768, CV_8UC3);
src.setTo(Scalar(255, 200, 100));

Mat roi = src(Rect(100, 100, 300, 300));
cvtColor(roi, roi, CV_RGB2GRAY);  // nothing changed, still src is the same after cvtColor

你可以做的是执行转换灰度在所选的roi中，什么不涉及复制，而是工作到位：

What you can do is to perform conversion to grayscale by hand in the selected roi, what does not involve copying, rather that works in place:

    Mat src(1024, 768, CV_8UC3);
    src.setTo(cv::Scalar(255, 200, 100));

    cv::imwrite("out.jpg", src);

    Mat roi = src(cv::Rect(100, 100, 300, 300));

    for(int i=0;i<roi.cols;i++)
        for(int j=0;j<roi.rows;j++) {
            cv::Vec3b p = roi.at<cv::Vec3b>(j,i);
            unsigned char lumination = (unsigned char)( 0.2126*p[2] + 0.7152*p[1] + 0.0722*p[0]);
            p[0] = p[1] = p [2] = lumination;   
            roi.at<cv::Vec3b>(j,i) = p;
        }

编辑：这里是一个lena示例：

here's a lena example:

Mat src = imread("lena.jpg");
Mat roi = src(cv::Rect(src.cols/4, src.cols/4, src.cols/2, src.rows/2));

for(int i=0;i<roi.cols;i++)
    for(int j=0;j<roi.rows;j++) {
        cv::Vec3b p = roi.at<cv::Vec3b>(j,i);
        unsigned char lumination = (unsigned char)( 0.2126*p[2] + 0.7152*p[1] + 0.0722*p[0]);
        p[0] = p[1] = p [2] = lumination;   
        roi.at<cv::Vec3b>(j,i) = p;
    }
cv::imwrite("out.jpg", src);

结果：

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