I got a problem where I need to access pixels of a opencv Mat image container. I use opencv inRange function to create a mask. In that mask I need to check the value of different pixels, but I won't receive the values I expect to receive.

// convert image to hsv for better color-detection
cv::Mat img_hsv, maskR, maskY, mask1, mask2;
cv::cvtColor(image, img_hsv, cv::COLOR_BGR2HSV);
// Gen lower mask (0-5) and upper mask (175-180) of RED
cv::inRange(img_hsv, cv::Scalar(0, 50, 20), cv::Scalar(5, 255, 255), mask1);
cv::inRange(img_hsv, cv::Scalar(175, 50, 20), cv::Scalar(180, 255, 255), mask2);
// Merge the masks
cv::bitwise_or(mask1, mask2, maskR);

after that I try to read the pixel values where I got extremely high values and even nans, but most of them zeros, which is expected as the mask is only black and white

if (maskR.at<double>(position.x, position.y) == 255) 

is there something I'm missing? I tried with double, uchar, int and float

when I print the mask, I can clearly see the 0 and 255 entries(no nans or strange numbers), but when I access them with the at() function, I wont get the same results.

The coordinates of the pixels should be in the range of the Mat as the dimension of the mask is 1080x1920 and non of the coordinates reach over that.

I got the dimension by using cv::size

CodePudding user response：

I finnaly found the answer to my own question. It works when I use uchar:

maskR.at<uchar>(position.x, position.y) == 255

I thought this wouldn't work because printing this with std::cout wouldn't give me an output, but the reason for that is that I forgot to cast uchar so it could be printed in the console