Computer Vision Foundations · free preview

Quadrature Pairs and Local Amplitude

Pairing a filter with its ninety-degree phase partner and summing squares yields local amplitude, a polarity-invariant measurement of structure that a two-channel network computes in one pass.

1. The missing partner

The missing partner

2. Amplitude from two phases

Amplitude from two phases

3. Polarity stops mattering

Polarity stops mattering

4. A two-channel machine

A two-channel machine

5. Why the pair has no blind phase

A cosine-phase filter produces zero response on a stripe patch shifted a quarter cycle. How does adding the sine-phase partner fix this?

6. Amplitude on opposite edges

A bright-on-dark edge and a dark-on-bright edge pass through the same quadrature pair. Compare the linear responses and the local amplitudes.

7. Amplitude of a pair

A quadrature pair returns h = 3 and q = 4 at some position. Write the local amplitude a.

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