TABLE OF CONTENTS In Chapter 21 we looked at methods for removing distracting elements of an image based on color values. Sometimes patterns exist in images that may not have color value, preventing a color isolation technique from working. Examples of patterns that may be removed with a Fast Fourier Transform (FFT) include an interference pattern in a video, a security pattern behind a fingerprint, and the cloth weave pattern behind a bloody footprint. If the pattern is consistent, it may be possible to remove the pattern while retaining the remaining valuable information in the image using an FFT filter.
There is no FFT filter built directly into Photoshop, so in this chapter we'll use a plug-in from Ocean Systems called ClearID and also a separate program called ImageJ from the National Institutes of Health. I'll show you how to get both of these tools.
ClearID, from Ocean Systems, consists of several plug-in filters and JavaScript scripts that expand on the built-in functionality of Photoshop. These include filters and features for deblurring, noise reduction, frame averaging, an FFT filter, and others. A demo version of ClearID is included on this book's companion CD.
These tools can all be accessed directly from the Filter menu, but they can also be accessed by using scripts from the File > Scripts menu. When these filters are used with the scripts, they will convert your image to 16 bit if it isn't already. They will also warn you if the visibility is...
