ABSTRACT
The word spectrum has several meanings. In signal processing, the spec trum of a signal is a particular kind of mapping function. In the case of a waveform, the spectrum maps the signal from the time domain into the frequency domain, where we can see exactly how the signal content is dis tributed over frequency. In the case of an image, the spectrum maps the signal from the spatial domain of the image into a two-dimensional fre quency domain. Sometimes the spectrum of a waveform or an image shows us things we can only see less clearly or even not see at all, when we look at the signal in the time domain. We will see some examples of this later in this chapter.
