Pyramids are multiple copies of the same images that differ in their sizes. They are represented as layers, as shown in the following figure. Each level in the pyramid is obtained by reducing the rows and columns by half. Thus, effectively, we make the image's size one quarter of its original size:
Pyramids intrinsically define reduce and expand as their two operations. Reduce refers to a reduction in the image's size, whereas expand refers to an increase in its size.
We will use a convention that lower levels in a pyramid mean downsized images and higher levels mean upsized images.
In the ...