A Photoshop Wavelet Workout

(not totally finished but well worth a look)

Presentation and requirement

This collection of exercises teaches how to implement wavelet filters in Photoshop and how they can be used for image compression.

It has been designed with Photoshop 5 and has been used by students with Photoshop 6. It requires a photoshop plugin called 'Filter Factory', which is part of the Photoshop package but is not installed when using the 'easy install' option. You may read the Filter factory documentation here. If you do not have Filter Factory or if it is not supported anymore by your application, you can try FilterFoundry, which is compatible and is available for Windows and Mac. Once you have installed the Filter Factory plugin, it should be available in the 'synthetic' filter category (or 'Telegraphics' if you use FilterFoundry). Print the manual (you will need it).

This is a preview of the image we are going to work with:

You will have to download the full 1024x1024 image to do the exercises. It has the advantage of having dimensions which are a power of 2; however, you may work with an image of any size, except that you may end up with extra rows or colums at the image reconstruction.

The exercise is basically an implementation of a wavelet decomposition and reconstruction using filter banks. We will also perform some basic image processing on the wavelet transform.

Let us have a look at the structure of these filters.