How to Efficiently Access Pixel Channel Values in OpenCV Mat Images?
Nov 23, 2024 am 08:46 AM
Retrieving Pixel Channel Values from OpenCV Mat Representations
To obtain the channel value for a specific pixel within an OpenCV Mat image, you can utilize the following methods:
Method 1: Using OpenCV's Vec3b
For Mat images of type CV_8UC3, containing three channels (blue, green, and red), the Vec3b data structure can be employed:
for(int i = 0; i < foo.rows; i++)
{
for(int j = 0; j < foo.cols; j++)
{
Vec3b bgrPixel = foo.at<Vec3b>(i, j);
// Access individual channel values:
uint8_t blue = bgrPixel[0];
uint8_t green = bgrPixel[1];
uint8_t red = bgrPixel[2];
}
}
Method 2: Direct Buffer Access
For improved performance, direct access to the image data buffer can be utilized:
uint8_t* pixelPtr = (uint8_t*)foo.data;
int cn = foo.channels(); // Number of channels per pixel
for(int i = 0; i < foo.rows; i++)
{
for(int j = 0; j < foo.cols; j++)
{
// Retrieve channel values:
uint8_t blue = pixelPtr[i*foo.cols*cn + j*cn + 0];
uint8_t green = pixelPtr[i*foo.cols*cn + j*cn + 1];
uint8_t red = pixelPtr[i*foo.cols*cn + j*cn + 2];
}
}
Note: OpenCV internally stores pixel data in BGR (blue, green, red) format, rather than RGB.
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