"""
Source code from:
https://github.com/clovaai/voxceleb_trainer/blob/master/tuneThreshold.py
"""
from operator import itemgetter
import numpy
from sklearn import metrics
[docs]def tuneThresholdfromScore(scores, labels, target_fa, target_fr=None):
fpr, tpr, thresholds = metrics.roc_curve(labels, scores, pos_label=1)
fnr = 1 - tpr
tunedThreshold = []
if target_fr:
for tfr in target_fr:
idx = numpy.nanargmin(numpy.absolute((tfr - fnr)))
tunedThreshold.append([thresholds[idx], fpr[idx], fnr[idx]])
for tfa in target_fa:
idx = numpy.nanargmin(
numpy.absolute((tfa - fpr))
) # numpy.where(fpr<=tfa)[0][-1]
tunedThreshold.append([thresholds[idx], fpr[idx], fnr[idx]])
idxE = numpy.nanargmin(numpy.absolute((fnr - fpr)))
eer = max(fpr[idxE], fnr[idxE]) * 100
return (tunedThreshold, eer, fpr, fnr)
# Creates a list of false-negative rates, a list of false-positive rates
# and a list of decision thresholds that give those error-rates.
[docs]def ComputeErrorRates(scores, labels):
# Sort the scores from smallest to largest, and also get the corresponding
# indexes of the sorted scores. We will treat the sorted scores as the
# thresholds at which the the error-rates are evaluated.
sorted_indexes, thresholds = zip(
*sorted(
[(index, threshold) for index, threshold in enumerate(scores)],
key=itemgetter(1),
)
)
sorted_labels = []
labels = [labels[i] for i in sorted_indexes]
fnrs = []
fprs = []
# At the end of this loop, fnrs[i] is the number of errors made by
# incorrectly rejecting scores less than thresholds[i]. And, fprs[i]
# is the total number of times that we have correctly accepted scores
# greater than thresholds[i].
for i in range(0, len(labels)):
if i == 0:
fnrs.append(labels[i])
fprs.append(1 - labels[i])
else:
fnrs.append(fnrs[i - 1] + labels[i])
fprs.append(fprs[i - 1] + 1 - labels[i])
fnrs_norm = sum(labels)
fprs_norm = len(labels) - fnrs_norm
# Now divide by the total number of false negative errors to
# obtain the false positive rates across all thresholds
fnrs = [x / float(fnrs_norm) for x in fnrs]
# Divide by the total number of corret positives to get the
# true positive rate. Subtract these quantities from 1 to
# get the false positive rates.
fprs = [1 - x / float(fprs_norm) for x in fprs]
return fnrs, fprs, thresholds
# Computes the minimum of the detection cost function. The comments refer to
# equations in Section 3 of the NIST 2016 Speaker Recognition Evaluation Plan.
[docs]def ComputeMinDcf(fnrs, fprs, thresholds, p_target, c_miss, c_fa):
min_c_det = float("inf")
min_c_det_threshold = thresholds[0]
for i in range(0, len(fnrs)):
# See Equation (2). it is a weighted sum of false negative
# and false positive errors.
c_det = c_miss * fnrs[i] * p_target + c_fa * fprs[i] * (1 - p_target)
if c_det < min_c_det:
min_c_det = c_det
min_c_det_threshold = thresholds[i]
# See Equations (3) and (4). Now we normalize the cost.
c_def = min(c_miss * p_target, c_fa * (1 - p_target))
min_dcf = min_c_det / c_def
return min_dcf, min_c_det_threshold