Image Pyramids

There are two common kinds of image pyramids:
– Gaussian pyramid: Used to downsample images
– Laplacian pyramid: Used to reconstruct an upsampled image from an image lower in the pyramid (with
less resolution)

• In this tutorial we’ll use the Gaussian pyramid

Imagine the pyramid as a set of layers in which the higher the layer, the smaller the size.

Notice that it is important that the input image can be divided by a factor of two (in both dimensions).
Otherwise, an error will be shown.
– Finally, we update the input image tmp with the current image displayed, so the subsequent operations

are performed on it.

#include <opencv.hpp>

using namespace cv;
/// Global variables
Mat src, dst, tmp;
char* window_name = "Pyramids Demo";
/**
* @function main
*/
int main(int argc, char** argv)
{
	/// General instructions
	printf("\n Zoom In-Out demo \n ");
	printf("------------------ \n");
	printf(" * [u] -> Zoom in \n");
	printf(" * [d] -> Zoom out \n");
	printf(" * [ESC] -> Close program \n \n");
	/// Test image - Make sure it s divisible by 2^{n}
	src = imread("beauty.jpg");
	if (!src.data)
	{
		printf(" No data! -- Exiting the program \n");
		return -1;
	}
	tmp = src;
	dst = tmp;
	/// Create window
	namedWindow(window_name, CV_WINDOW_AUTOSIZE);
	imshow(window_name, dst);
	/// Loop
	while (true)
	{
		int c;
		c = waitKey(10);
		if ((char)c == 27)
		{
			break;
		}
		if ((char)c == 'u')
		{
			pyrUp(tmp, dst, Size(tmp.cols * 2, tmp.rows * 2));
			printf("** Zoom In: Image x 2 \n");
		}
		else if ((char)c == 'd')
		{
			pyrDown(tmp, dst, Size(tmp.cols / 2, tmp.rows / 2));
			printf("** Zoom Out: Image / 2 \n");
		}
		imshow(window_name, dst);
		tmp = dst;
	}
	return 0;
}

beauty.jpg