c++ - 如何访问 3D CV::Mat 的索引

Question

我在尝试访问 3D CV::Mat 的索引时遇到段错误。代码如下，

int channel = 3;
int sizes[] = { imageheight, imageWidth};
CV::Mat test(2, sizes, CV_8UC3)
for(int i=0;i<image2D->size();i++)
    {
        Point2D &_point = image2D->at(i);       

        test.at<unsigned char>(_point.y,_point.x,0) = _point.rgb.r;
        test.at<unsigned char>(_point.y,_point.x,1) = _point.rgb.g;
        test.at<unsigned char>(_point.y,_point.x,2) = _point.rgb.b; // Segmentation fault in this line
    }

以下方式不会崩溃，但会输出黑色图像。我不确定我做的是否正确，

unsigned char *ptest = test.ptr<unsigned char>(_point.y);
        ptest[channel*_point.x+ 0] = _point.rgb.r;
        ptest[channel*_point.x+ 1] = _point.rgb.g;
        ptest[channel*_point.x+ 2] = _point.rgb.b;

编辑:

将代码更新为以下代码会出现编译错误invalid types ‘unsigned char[int]’ for array subscript，

Matrix test(imageheight, imageWidth, CV_8UC3);
for(int i=0;i<image2D->size();i++)
    {
        Point2D &_point = image2D->at(i);
        // Compile error on the below 3 lines.
        test.at<unsigned char>(_point.y, _point.x)[0] = _point.rgb.b;
        test.at<unsigned char>(_point.y, _point.x)[1] = _point.rgb.g;
        test.at<unsigned char>(_point.y, _point.x)[2] = _point.rgb.r;

    }

编译错误在我用[]访问 channel 索引的位置。我想这不是访问 channel 的正确方式。

Answer 1

使用多个 channel 访问 cv::Mat 的最简单方法，

cv::Mat3b test(imageheight, imageWidth, CV_8UC3);
for(int i=0;i<image2D->size();i++)
{
    Point2D &_point = image2D->at(i);
    test.at<cv::Vec3b>(_point.y, _point.x)[0] = _point.rgb.b;
    test.at<cv::Vec3b>(_point.y, _point.x)[1] = _point.rgb.g;
    test.at<cv::Vec3b>(_point.y, _point.x)[2] = _point.rgb.r;
}

对于单 channel cv::Mat

cv::Mat test(imageheight, imageWidth, CV_32FC1);

for(int i=0;i<image2D->size();i++)
{
    Point2D &_point = image2D->at(i);
    test.at<float>(_point.y, _point.x) = _point.r;
}

多亏了这个answer .