在OpenCV 2.x中具有像素访问的错误 [英] Bug with pixel access in OpenCV 2.x

问题描述

我在尝试找到如何在新版本（2.x）的OpenCV中访问rgb像素时遇到问题。

这是我的代码

  #include< opencv2\imgproc\imgproc.hpp> 
 #include< opencv2\highgui\highgui.hpp> 
 
 using namespace cv; 
 using namespace std; 
 
 int main（int argc，char * argv []）
 {
 Mat img; 
 
 
 string winMain =Main; 
 
 img = imread（argv [1]）; 
 
 for（int j = 0; j  {
 for（int i = 0; i  {
 img.data [j * img.cols + i * 3 + 0] =（uchar）0; // B 
 //img.data [j * img.cols + i + 1] =（uchar）0; // G 
 //img.data [j * img.cols + i + 2] =（uchar）0; // R 
} 
} 
 
 namedWindow（winMain）; 
 
 imshow（winMain，img）; 
 
 waitKey（）; 
 
 return 1; 
} 
  

正如你可以注意到在下面的例子中，修改。

）：

使用OP的代码生成的结果：

使用修改后的代码结果（ j * img.cols * 3 ）：

I'm having trouble trying to find out how to access rgb pixel in the new version (2.x) of OpenCV. I tried using a mix of the old and the new method but without success.

Here is my code

#include <opencv2\imgproc\imgproc.hpp>
#include <opencv2\highgui\highgui.hpp>

using namespace cv;
using namespace std;

int main (int argc, char* argv[])
{
Mat img;


string winMain = "Main";

img = imread(argv[1]);

for (int j = 0; j < img.rows; j++)
{
    for (int i = 0; i < img.cols; i++)
    {
        img.data[j * img.cols + i * 3 + 0] = (uchar)0; //B
        //img.data[j * img.cols + i + 1] = (uchar)0; //G
        //img.data[j * img.cols + i + 2] = (uchar)0; //R
    }
}

namedWindow(winMain);

imshow(winMain, img);

waitKey();  

return 1;
}

As you can notice in the following example, only a third of the image is modified.

Link to example

Thanks for helping

解决方案

I tested out your code, and I found the bug. You multiplied the column index by 3 (i * 3), but it's also necessary to multiply the row index by 3 (j * img.cols * 3).

I replaced j * img.cols with j * img.cols * 3:

for (int j = 0; j < img.rows; j++)
{
    for (int i = 0; i < img.cols; i++)
    {
        img.data[j * img.cols * 3 + i*3 + 0] = (uchar)0; //B
        //img.data[j * img.cols * 3 + i*3 + 1] = (uchar)0; //G
        //img.data[j * img.cols * 3 + i*3 + 2] = (uchar)0; //R
    }
}

Let's try an example.

Example image (from MIT pedestrian dataset):

Result using OP's code:

Result using the revised code (with j * img.cols * 3):

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