PiCapture

Simple OpenCV wrapper for the Raspberry PI Camera Module

This is based on Samarth Brahmbatt's code listed on his title: Practical OpenCV. Modified by George Profenza for a simpler/faster colour callback and added camera settings. The setter methods are minimally commented to include ranges for the available parameters.

How to use the sample

First you need to fetch the userland repo

git clone https://github.com/raspberrypi/userland.git

Then replace USERLAND_DIR in CMakeLists.txt with the path to the userland repo you just downloaded/cloned.

Finally, build the demo:

mkdir build && cd build
cmake ..
make
./main

By default this will open the camera in grayscale mode. Pass any command line argument to main and it will start in colour

Note

For the BGR encoding mode make sure you have updated your Pi to the latest version

sudo rpi-update

The color mode has been tested with firmware 3.10.36+ #665 and the conversion is on the GPU in this case.

If for some reason you don't want to update, you can use this color callback:

static void color_callback(MMAL_PORT_T *port, MMAL_BUFFER_HEADER_T *buffer) {
	MMAL_BUFFER_HEADER_T *new_buffer;
	mmal_buffer_header_mem_lock(buffer);
	unsigned char* pointer = (unsigned char *)(buffer -> data);
	int w = PiCapture::width, h = PiCapture::height;
	Mat y(h, w, CV_8UC1, pointer);
	pointer = pointer + (h*w);
	Mat u(h/2, w/2, CV_8UC1, pointer);
	pointer = pointer + (h*w/4);
	Mat v(h/2, w/2, CV_8UC1, pointer);
	resize(u, u, Size(), 2, 2, INTER_NEAREST);
	resize(v, v, Size(), 2, 2, INTER_NEAREST);
	int from_to[] = {0, 0};
	mixChannels(&y, 1, &image, 1, from_to, 1);
	from_to[1] = 1;
	mixChannels(&v, 1, &image, 1, from_to, 1);
	from_to[1] = 2;
	mixChannels(&u, 1, &image, 1, from_to, 1);
	cvtColor(image, image, CV_YCrCb2BGR);
	int from_to[] = {0, 0};
	 mixChannels(&r, 1, &image, 1, from_to, 1);
    	from_to[1] = 1;
    	mixChannels(&g, 1, &image, 1, from_to, 1);
    	from_to[1] = 2;
    	mixChannels(&b, 1, &image, 1, from_to, 1);
	PiCapture::set_image(image);
}

and you need to make sure you are using YUV encoding in the constructor (I420 instead of RGB24)

		format->encoding = MMAL_ENCODING_I420;
		format->encoding_variant = MMAL_ENCODING_I420;

This would be a wee bit slower as the conversion is done on the CPU, but will work on older firmware