Opencv Mat create Image

Question

I am trying to load BGR image and than copy some pixels that certifies some condition to a new image which i created using the loaded images width, height and type. The type is CV_8UC3.

Mat initial_Image = imread("image.jpg");
Mat image(img.rows,img.cols, CV_8UC3);

cout<<initial_Image.type()<<endl;

for(int i = 0;i < img.cols ;i++)
{
for(int j = 0;j < img.rows ;j++)
{
Vec3b intensity = initial_Image.at<Vec3b>(j,i);
uchar blue = intensity.val[0];
uchar green = intensity.val[1];
uchar red = intensity.val[2];


image.at<uchar>(j,i) = blue;
image.at<uchar>(j+1,i+1) = green;
image.at<uchar>(j+2,i+2) = red ;

    }
}
out.close();

imshow("im", image);

I have not placed the condition but i just tried to copy all the respective pixels from the read image into the new create image.

My problem is the the read image is 3 channle RGB but when i plot the image by copying the pixel into the new created image it gives me a black and white image which is divide by 3. WHY? Since i have to change the pixles values once i get this working based on some conditions, i cannot use copyto function as some might suggest. The reason i put not condition is to ease the work of getting the correction done. THank u.

Answer 1

The way you are indexing image is not right. The current way you are indexing image will write blue to index j,i, and then when you reach the next column a blue pixel will get written to j+1,i+1 effectively overwriting the green value. Instead you should be indexing image using .at<Vec3b>.

The easiest way would be to do it like this:

image.at<Vec3b>(j,i) = initial_Image.at<Vec3b>(j,i);

If you want to change red, blue, and green you could also do it this way:

Vec3b intensity = initial_Image.at<Vec3b>(j,i);
uchar blue = intensity.val[0];
uchar green = intensity.val[1];
uchar red = intensity.val[2];

//Do stuff with blue, green, and red

image.at<Vec3b>(j,i) = Vec3b(blue,green,red);