How to set a pixel to a value in a cv::Mat object?

Question

I need to set a single pixel in the Mat object to a certain value.

How to do it?

I am using openCV 2.1 with visual studio 2010.

Answer 1

如果您正在处理uchar（CV_8U）矩阵：

 mat.at<uchar>(row, column, channel) = val;

Answer 2

In fact, there are 4 kinds of methods to get/set a pixel value in a cv::Mat object as described in the OpenCV tutorial .

The one @Régis mentioned is called On-The-Fly RA in OpenCV tutorial. It's the most convenient but also time-consuming.

Based on the tutorial's experiment , it also lists performance differences in all the 4 methods.

• Efficient Way 79.4717 milliseconds
• Iterator 83.7201 milliseconds
• On-The-Fly RA 93.7878 milliseconds
• LUT function 32.5759 milliseconds

Answer 3

Here's an example:

vector<cv::Point3f> xyzBuffer;
cv::Mat xyzBuffMat = cv::Mat(307200, 1, CV_32FC3);
for (int i = 0; i < xyzBuffer.size(); i++) {
    xyzBuffMat.at<cv::Vec3f>(i, 1, 0) = xyzBuffer[i].x;
    xyzBuffMat.at<cv::Vec3f>(i, 1, 1) = xyzBuffer[i].y;
    xyzBuffMat.at<cv::Vec3f>(i, 1, 2) = xyzBuffer[i].z;
}