Esempio: trasformate wavelet

Funzioni > Trasformate e filtri > Esempio: trasformate wavelet

Utilizzare le funzioni per le trasformate wavelet per comprimere dati.

1. Definire un segnale ad onda quadra, in cui:

2. Valutare l'array n e tracciare il grafico del segnale S:

Fare clic per copiare questa espressione

Nell'intervallo 0..255 l'ampiezza del segnale S è uguale a 1 per tutti i valori di n (96..160) e uguale a 0 negli altri casi.

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3. Utilizzare la funzione wave per calcolare la trasformata wavelet del segnale S:

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4. Calcolare il numero di livelli contenuti in questa trasformata:

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5. Utilizzare le funzioni submatrix e floor per acquisire il senso dell'importanza relativa di ogni livello:

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6. Tracciare il grafico di diversi livelli di coefficienti contemporaneamente:

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7. Rappresentare il segnale con una minor quantità di dati eseguendo le due operazioni indicate di seguito.

a. Azzerare i coefficienti di livello superiore.

b. Calcolare la trasformata wavelet inversa dei nuovi vettori di coefficienti.

Primo livello in cui i coefficienti vengono azzerati (L < 7 può variare).

8. Utilizzare la funzione iwave per recuperare il segnale originale:

9. Confrontare il segnale originale con il segnale trasformato e tracciarne il grafico:

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Questa tecnica consente di comprimere i dati necessari per rappresentare un segnale.

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