Images, sampling and frequency domain processing - Feature Extraction and Image Processing - page 44

Signal

Time

∆ t
(a) Sampled signal

Frequency response

Frequency

-f sample
= -1/ ∆

-f max f max f sample

= 1/ ∆

t t

(b) Oversampled spectra

Frequency response

Frequency

-3f max -2f max

= -f sample

-f max f max 2f max

= f sample

3f max

(c) Sampling at the Nyquist rate

Frequency response

Frequency

-f sample -f max f max f sample

(d) Undersampled, aliased, spectra

Figure 2.9 Sampled spectra