小波影象處理 —— 奇異點(不連續點)檢測
阿新 • • 發佈:2019-02-01
動態系統(dynamic system)中的訊號常常表現出瞬時(transient)急劇的變化,一般為幅度的突然跳躍或一階導二階導數值的尖銳變化。傅立葉分析通常無法檢測出這種瞬時的變化,小波分析卻可以檢測和捕捉到訊號在某一時刻的突變。
1. 頻率跳變(frequency breakdown)
load freqbrk
x = freqbrk;
level = 1;
[c, l] = wavedec(x, level, 'haar');
d = detcoef(c, l, level);
subplot(1, 2, 1), plot(x)
subplot(1, 2, 2), plot (interpft(d, 2*length(d)))
2. 二階導跳變(second derivation breakdown)
load scddvbrk
x = scddvbrk;
level = 2;
[c, l] = wavedec(x, level, 'db4');
[d1, d2] = detcoef(c, l, 1:level);
% 上取樣;
d1up = dyadup(d1, 0);
d2up = dyadup(dyadup(d2, 0), 0);
subplot(131), plot(x), xlim([400, 600])
subplot(132), plot(d1up), xlim ([400, 600])
subplot(133), plot(d2up), xlim([400, 600])