CODEWITHSUNDEEP
c++opencv
Mohammad Saifullah
Mohammad Saifullah

Reputation: 1143

Open CV: Acces pixels of grayscale image

I know this question can be wired for experts, but I want to access pixels of grayscale image in openCV. I am using the following code:

cv::Mat img1 = cv::imread("bauckhage.jpg", CV_LOAD_IMAGE_GRAYSCALE);

Now if I want to print any pixel(say at position 255,255) using img1.at<float>(255,255) I get 0, which is not actually black pixel. I thought the image has been read as 2d Matrix.

Actually I want to do some calculation on each pixel, for that I need to access each pixel explicitly.

Any help or suggestion will be appreciated.

Upvotes: 1

Views: 2799

Answers (2)

sleeping_dragon
sleeping_dragon

Reputation: 711

You will have to do this

   int x = (int)(img.at<uchar>(j,i))

This is because of the way the image is stored and the way img.at works. Grayscale image is stored in CV_8UC1 format and hence it is basically an array of uchar type. So the return value is a uchar which you typecast into an int to operate on it as ints.

Also, this is similar to your questions: accessing pixel value of gray scale image in OpenCV

Upvotes: 3

berak
berak

Reputation: 39816

float is the wrong type here.

if you read an image like this:

cv::Mat img1 = cv::imread("bauckhage.jpg", CV_LOAD_IMAGE_GRAYSCALE);

then it's type will be CV_8U, (uchar, a single grayscale byte per pixel). so, to access it:

uchar &pixel = img1.at<uchar>(row,col);

Upvotes: 1

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