how to reduce image using Gaussian Pyramid Decomposition

The image reduction step involves lowpass filtering and downsampling the image pixels. The image expansion step involves upsampling the image pixels and lowpass filtering.


Example
gaussPyramid = vision.Pyramid('PyramidLevel', 2);
I = im2single(imread('cameraman.tif'));                 
J = step(gaussPyramid, I);
figure, imshow(I); title('Original Image');
figure, imshow(J); title('Reduced Image');