OpenCV 2.3: Convert Mat to RGBA pixel array

c++, opencv, sfml, webcam

Solution

OpenCV can do all job for you:

VideoCapture cap(0);
Mat frame;
cap >> frame;

uchar* camData = new uchar[frame.total()*4];
Mat continuousRGBA(frame.size(), CV_8UC4, camData);
cv::cvtColor(frame, continuousRGBA, CV_BGR2RGBA, 4);
img.LoadFromPixels(frame.cols, frame.rows, camData);

Problem

I am attempting to use OpenCV to grab frames from a webcam and display them in a window using SFML. VideoCapture returns frames in OpenCV's Mat format. To display the frames, SFML requires a 1D array of pixels in its uint8 format, which (as far as I can tell) is interchangeable with uchar. This array is expected to represent 32 bits per pixel RGBA. So, I have a uchar array, and I'm looping over the Mat data and copying each pixel: ``` VideoCapture cap(0); Mat frame; cap >> frame; uchar* camData = new uchar[640*480*4]; uchar* pixelPtr = frame.data; for(int i = 0; i < frame.rows; i++) { for(int j = 0; j < frame.cols; j++) { camData[i*frame.cols + j + 2] = pixelPtr[i*frame.cols + j + 0]; // B camData[i*frame.cols + j + 1] = pixelPtr[i*frame.cols + j + 1]; // G camData[i*frame.cols + j + 0] = pixelPtr[i*frame.cols + j + 2]; // R camData[i*frame.cols + j + 3] = 255; } } img.LoadFromPixels(640, 480, camData); //Load pixels into SFML Image object for display ``` Unfortunately, this doesn't quite work. Something in that loop is wrong, as the resulting image when I load and display camData is scrambled. As far as I can discern, either my math in the loop is wrong so the pixels are being assigned wrong, or the Mat data is in some format other than BGR. Any ideas?

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