JavaScript image processing: Image pyramid

Objective

In a previous article, we explained the edge gradient computing function, which we'll look at in the image pyramid.

Image pyramid?

Image pyramid is widely used in computer vision applications.

Image Pyramid is an image set, all the images in the set originate from the same original image, and are obtained by successive descending sampling of the original image.

--"Learning OpenCV"

The common image pyramid has the following two kinds:

Gauss Pyramid (Gaussian pyramid): Used to sample down

Laplace pyramid (Laplacian Pyramid): Used to reconstruct upper-layer images from the lower pyramid image

Gauss Pyramid

Like the pyramid, the Gaussian pyramid is gradually sampled from the underlying original graph, getting smaller and lower.

So how do you get the next layer of images?

First, and the Gaussian kernel convolution:

Then, delete all the even rows.

Visible, this next level of image is about 1/4 of the previous level.

So how does the upward transformation change?

First, expand the row of pictures to twice times the original, and then add the rows and columns with a 0 fill.

Finally, multiply the volume by 4 after the Gaussian kernel.