From a084afd1028f3aba5bfe883d696d0c8954b14f33 Mon Sep 17 00:00:00 2001
From: Guillaume HEUSCH <guillaume.heusch@idiap.ch>
Date: Wed, 4 Jul 2018 11:34:26 +0200
Subject: [PATCH] [extractor] corrected 2-3 (minor ?) bugs on the feature
computation
---
bob/pad/face/extractor/LTSS.py | 24 ++++++++++++++++++++----
1 file changed, 20 insertions(+), 4 deletions(-)
diff --git a/bob/pad/face/extractor/LTSS.py b/bob/pad/face/extractor/LTSS.py
index 2177e1ed..a47475d7 100644
--- a/bob/pad/face/extractor/LTSS.py
+++ b/bob/pad/face/extractor/LTSS.py
@@ -56,7 +56,10 @@ class LTSS(Extractor, object):
"""
super(LTSS, self).__init__(**kwargs)
self.framerate = framerate
+
+ # TODO: try to use window size as NFFT - Guillaume HEUSCH, 04-07-2018
self.nfft = nfft
+
self.debug = debug
self.window_size = window_size
self.concat = concat
@@ -80,27 +83,40 @@ class LTSS(Extractor, object):
# log-magnitude of DFT coefficients
log_mags = []
-
+
# go through windows
for w in range(0, (signal.shape[0] - self.window_size), window_stride):
+
+ # n is even, as a consequence the fft is as follows [y(0), Re(y(1)), Im(y(1)), ..., Re(y(n/2))]
+ # i.e. each coefficient, except first and last, is represented by two numbers (real + imaginary)
fft = rfft(signal[w:w+self.window_size], n=self.nfft)
- mags = numpy.zeros(int(self.nfft/2), dtype=numpy.float64)
- # XXX : bug was here (no clipping)
+ # the magnitude is the norm of the complex numbers, so its size is n/2 + 1
+ mags = numpy.zeros((int(self.nfft/2) + 1), dtype=numpy.float64)
+
+ # first coeff is real
if abs(fft[0]) < 1:
mags[0] = 1
else:
mags[0] = abs(fft[0])
- # XXX
+ # go through coeffs 2 to n/2
index = 1
for i in range(1, (fft.shape[0]-1), 2):
mags[index] = numpy.sqrt(fft[i]**2 + fft[i+1]**2)
if mags[index] < 1:
mags[index] = 1
index += 1
+
+ # last coeff is real too
+ if abs(fft[-1]) < 1:
+ mags[index] = 1
+ else:
+ mags[index] = abs(fft[-1])
+
log_mags.append(numpy.log(mags))
+ # build final feature
log_mags = numpy.array(log_mags)
mean = numpy.mean(log_mags, axis=0)
std = numpy.std(log_mags, axis=0)
--
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