OpenCV get pixel channel value from Mat image
Solution 1:
Assuming the type is CV_8UC3 you would do this:
for(int i = 0; i < foo.rows; i++)
{
for(int j = 0; j < foo.cols; j++)
{
Vec3b bgrPixel = foo.at<Vec3b>(i, j);
// do something with BGR values...
}
}
Here is the documentation for Vec3b. Hope that helps! Also, don't forget OpenCV stores things internally as BGR not RGB.
EDIT :
For performance reasons, you may want to use direct access to the data buffer in order to process the pixel values:
Here is how you might go about this:
uint8_t* pixelPtr = (uint8_t*)foo.data;
int cn = foo.channels();
Scalar_<uint8_t> bgrPixel;
for(int i = 0; i < foo.rows; i++)
{
for(int j = 0; j < foo.cols; j++)
{
bgrPixel.val[0] = pixelPtr[i*foo.cols*cn + j*cn + 0]; // B
bgrPixel.val[1] = pixelPtr[i*foo.cols*cn + j*cn + 1]; // G
bgrPixel.val[2] = pixelPtr[i*foo.cols*cn + j*cn + 2]; // R
// do something with BGR values...
}
}
Or alternatively:
int cn = foo.channels();
Scalar_<uint8_t> bgrPixel;
for(int i = 0; i < foo.rows; i++)
{
uint8_t* rowPtr = foo.row(i);
for(int j = 0; j < foo.cols; j++)
{
bgrPixel.val[0] = rowPtr[j*cn + 0]; // B
bgrPixel.val[1] = rowPtr[j*cn + 1]; // G
bgrPixel.val[2] = rowPtr[j*cn + 2]; // R
// do something with BGR values...
}
}
Solution 2:
The below code works for me, for both accessing and changing a pixel value.
For accessing pixel's channel value :
for (int i = 0; i < image.cols; i++) {
for (int j = 0; j < image.rows; j++) {
Vec3b intensity = image.at<Vec3b>(j, i);
for(int k = 0; k < image.channels(); k++) {
uchar col = intensity.val[k];
}
}
}
For changing a pixel value of a channel :
uchar pixValue;
for (int i = 0; i < image.cols; i++) {
for (int j = 0; j < image.rows; j++) {
Vec3b &intensity = image.at<Vec3b>(j, i);
for(int k = 0; k < image.channels(); k++) {
// calculate pixValue
intensity.val[k] = pixValue;
}
}
}
`
Source : Accessing pixel value