Continuous mappings | Integral transforms
Continuous wavelet transform
In mathematics, the continuous wavelet transform (CWT) is a formal (i.e., non-numerical) tool that provides an overcomplete representation of a signal by letting the translation and scale parameter of the wavelets vary continuously. The continuous wavelet transform of a function at a scale (a>0) and translational value is expressed by the following integral where is a continuous function in both the time domain and the frequency domain called the mother wavelet and the overline represents operation of complex conjugate. The main purpose of the mother wavelet is to provide a source function to generate the daughter wavelets which are simply the translated and scaled versions of the mother wavelet. To recover the original signal , the first inverse continuous wavelet transform can be exploited. is the dual function of and is admissible constant, where hat means Fourier transform operator. Sometimes, , then the admissible constant becomes Traditionally, this constant is called wavelet admissible constant. A wavelet whose admissible constant satisfies is called an admissible wavelet. An admissible wavelet implies that , so that an admissible wavelet must integrate to zero. To recover the original signal , the second inverse continuous wavelet transform can be exploited. This inverse transform suggests that a wavelet should be defined as where is a window. Such defined wavelet can be called as an analyzing wavelet, because it admits to time-frequency analysis. An analyzing wavelet is unnecessary to be admissible. (Wikipedia).
