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njit-etd2003-081 - New Jersey Institute of Technology

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74<br />

The measure dadb used in the transform domain is consistent with the discussion<br />

a 2<br />

<strong>of</strong> the scaling property. Scaling by s while conserving the energy will spread the<br />

wavelet transform by s in both the dimensions a and b, and thus a renormalization by<br />

1<br />

a<br />

is necessary. It is worth noting that the wavelet transform energy between the<br />

different scales is also preserves such that<br />

3.7.3 Discrete Wavelet Transform<br />

Although the admissibility condition assures the complete representation <strong>of</strong> f (t) with its<br />

wavelet transform coefficients W f (a ,b) , it requires the wavelet transform operation to<br />

be performed for all values <strong>of</strong> a and b which are continuous parameters. This transform<br />

representation is not practical. One would prefer to perform the wavelet transform<br />

operation as few times as possible. Therefore these scaling or dilation, and translation or<br />

shift parameters, a and b respectively, are discretized. This discretization provides a<br />

transform grid or frame on the time-scale plane for the representation <strong>of</strong> signal f (t) . It<br />

is intuitive that this grid or frame should be defined properly such that the complete<br />

representation <strong>of</strong> f (t) is still possible. This is called the Discrete Wavelet Transform<br />

(DWT). This version <strong>of</strong> the wavelet transform reduces the redundancies <strong>of</strong> the wavelet<br />

space W f (a,b) significantly. The mathematical reasoning on the choice <strong>of</strong> frames or<br />

grids is perfectly treated in the literature.

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