annotate base/LogRange.cpp @ 519:21f86744d38e sv-v1.4

...
author Chris Cannam
date Thu, 11 Dec 2008 12:37:16 +0000
parents 1405f4a2caf3
children bdc9bb371a9f
rev   line source
Chris@224 1 /* -*- c-basic-offset: 4 indent-tabs-mode: nil -*- vi:set ts=8 sts=4 sw=4: */
Chris@224 2
Chris@224 3 /*
Chris@224 4 Sonic Visualiser
Chris@224 5 An audio file viewer and annotation editor.
Chris@224 6 Centre for Digital Music, Queen Mary, University of London.
Chris@224 7 This file copyright 2006 Chris Cannam.
Chris@224 8
Chris@224 9 This program is free software; you can redistribute it and/or
Chris@224 10 modify it under the terms of the GNU General Public License as
Chris@224 11 published by the Free Software Foundation; either version 2 of the
Chris@224 12 License, or (at your option) any later version. See the file
Chris@224 13 COPYING included with this distribution for more information.
Chris@224 14 */
Chris@224 15
Chris@224 16 #include "LogRange.h"
Chris@224 17
Chris@224 18 #include <algorithm>
Chris@464 19 #include <iostream>
Chris@224 20 #include <cmath>
Chris@224 21
Chris@224 22 void
Chris@224 23 LogRange::mapRange(float &min, float &max, float logthresh)
Chris@224 24 {
Chris@224 25 if (min > max) std::swap(min, max);
Chris@224 26 if (max == min) max = min + 1;
Chris@224 27
Chris@464 28 // std::cerr << "LogRange::mapRange: min = " << min << ", max = " << max << std::endl;
Chris@464 29
Chris@224 30 if (min >= 0.f) {
Chris@224 31
Chris@224 32 max = log10f(max); // we know max != 0
Chris@224 33
Chris@224 34 if (min == 0.f) min = std::min(logthresh, max);
Chris@224 35 else min = log10f(min);
Chris@224 36
Chris@464 37 // std::cerr << "LogRange::mapRange: positive: min = " << min << ", max = " << max << std::endl;
Chris@464 38
Chris@224 39 } else if (max <= 0.f) {
Chris@224 40
Chris@224 41 min = log10f(-min); // we know min != 0
Chris@224 42
Chris@224 43 if (max == 0.f) max = std::min(logthresh, min);
Chris@224 44 else max = log10f(-max);
Chris@224 45
Chris@224 46 std::swap(min, max);
Chris@224 47
Chris@464 48 // std::cerr << "LogRange::mapRange: negative: min = " << min << ", max = " << max << std::endl;
Chris@464 49
Chris@224 50 } else {
Chris@224 51
Chris@224 52 // min < 0 and max > 0
Chris@224 53
Chris@224 54 max = log10f(std::max(max, -min));
Chris@224 55 min = std::min(logthresh, max);
Chris@464 56
Chris@464 57 // std::cerr << "LogRange::mapRange: spanning: min = " << min << ", max = " << max << std::endl;
Chris@224 58 }
Chris@224 59
Chris@224 60 if (min == max) min = max - 1;
Chris@224 61 }
Chris@224 62
Chris@224 63 float
Chris@224 64 LogRange::map(float value, float thresh)
Chris@224 65 {
Chris@224 66 if (value == 0.f) return thresh;
Chris@224 67 return log10f(fabsf(value));
Chris@224 68 }
Chris@224 69
Chris@266 70 float
Chris@266 71 LogRange::unmap(float value)
Chris@266 72 {
Chris@266 73 return powf(10.0, value);
Chris@266 74 }
Chris@478 75
Chris@478 76 static float
Chris@478 77 sd(const std::vector<float> &values, size_t start, size_t n)
Chris@478 78 {
Chris@478 79 float sum = 0.f, mean = 0.f, variance = 0.f;
Chris@478 80 for (size_t i = 0; i < n; ++i) {
Chris@478 81 sum += values[start + i];
Chris@478 82 }
Chris@478 83 mean = sum / n;
Chris@478 84 for (size_t i = 0; i < n; ++i) {
Chris@478 85 float diff = values[start + i] - mean;
Chris@478 86 variance += diff * diff;
Chris@478 87 }
Chris@478 88 variance = variance / n;
Chris@478 89 return sqrtf(variance);
Chris@478 90 }
Chris@478 91
Chris@478 92 bool
Chris@478 93 LogRange::useLogScale(std::vector<float> values)
Chris@478 94 {
Chris@478 95 // Principle: Partition the data into two sets around the median;
Chris@478 96 // calculate the standard deviation of each set; if the two SDs
Chris@478 97 // are very different, it's likely that a log scale would be good.
Chris@478 98
Chris@478 99 if (values.size() < 4) return false;
Chris@478 100 std::sort(values.begin(), values.end());
Chris@478 101 size_t mi = values.size() / 2;
Chris@478 102
Chris@478 103 float sd0 = sd(values, 0, mi);
Chris@478 104 float sd1 = sd(values, mi, values.size() - mi);
Chris@478 105
Chris@478 106 std::cerr << "LogRange::useLogScale: sd0 = "
Chris@478 107 << sd0 << ", sd1 = " << sd1 << std::endl;
Chris@478 108
Chris@478 109 if (sd0 == 0 || sd1 == 0) return false;
Chris@478 110
Chris@478 111 // I wonder what method of determining "one sd much bigger than
Chris@478 112 // the other" would be appropriate here...
Chris@478 113 if (std::max(sd0, sd1) / std::min(sd0, sd1) > 10.f) return true;
Chris@478 114 else return false;
Chris@478 115 }
Chris@478 116