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hardware implementation of data compression ... - INFN Bologna

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132<br />

Wavelet based <strong>compression</strong> algorithm<br />

s<br />

a 5<br />

d 5<br />

d 4<br />

d 3<br />

−50<br />

40<br />

20<br />

d 0<br />

2 −20<br />

−40<br />

d 1<br />

150<br />

100<br />

50<br />

0<br />

30<br />

20<br />

10<br />

10<br />

0<br />

−10<br />

20<br />

0<br />

−20<br />

50<br />

0<br />

20<br />

0<br />

−20<br />

Decomposition at level 5 : s = a5 + d5 + d4 + d3 + d2 + d1 .<br />

1 2 3 4 5 6<br />

Figure 5.1: Uni-dimensional analysis on 5 levels <strong>of</strong> the signal S<br />

– the coefficients Cth have been synthesized into the signal R, using<br />

the filters H and G.<br />

Both in the uni-dimensional and in the bi-dimensional case, the performances<br />

related to <strong>compression</strong> have been quantified using the percentage<br />

P <strong>of</strong> the number <strong>of</strong> null coefficients in Cth, while the performances<br />

related to the reconstruction error have been quantified using the root<br />

mean square error E between the original signal S and the signal R,<br />

obtained after the analysis and synthesis <strong>of</strong> Cth.<br />

In particular, since the total number <strong>of</strong> elements in Cth is 65536, in<br />

the uni-dimensional case, the parameter P can be expressed in the<br />

following way:<br />

P =<br />

100 · (number <strong>of</strong> null coefficients in Cth)<br />

65536<br />

x 10 4<br />

(5.3)<br />

Even the total number <strong>of</strong> elements in S and in R is 65536, so, if si<br />

is the i-th element <strong>of</strong> the uni-dimensional signal S and ri is the i-th

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