annotate maths/MedianFilter.h @ 167:a82362d50144

Median filter standalone method, and tests

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    QM DSP Library

    Centre for Digital Music, Queen Mary, University of London.
    This file Copyright 2010 Chris Cannam.

    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

#ifndef MEDIAN_FILTER_H
#define MEDIAN_FILTER_H

#include <algorithm>
#include <cassert>
#include <cmath>
#include <iostream>
#include <vector>

template <typename T>
class MedianFilter
{
public:
    MedianFilter(int size, float percentile = 50.f) :
	m_size(size),
	m_frame(new T[size]),
	m_sorted(new T[size]),
	m_sortend(m_sorted + size - 1) {
        setPercentile(percentile);
	reset();
    }

    ~MedianFilter() { 
	delete[] m_frame;
	delete[] m_sorted;
    }

    void setPercentile(float p) {
        m_index = int((m_size * p) / 100.f);
        if (m_index >= m_size) m_index = m_size-1;
        if (m_index < 0) m_index = 0;
    }

    void push(T value) {
        if (value != value) return; // nan
	drop(m_frame[0]);
	const int sz1 = m_size-1;
	for (int i = 0; i < sz1; ++i) m_frame[i] = m_frame[i+1];
	m_frame[m_size-1] = value;
	put(value);
    }

    T get() const {
	return m_sorted[m_index];
    }

    T getAt(float percentile) {
	int ix = int((m_size * percentile) / 100.f);
        if (ix >= m_size) ix = m_size-1;
        if (ix < 0) ix = 0;
	return m_sorted[ix];
    }

    void reset() {
	for (int i = 0; i < m_size; ++i) m_frame[i] = 0;
	for (int i = 0; i < m_size; ++i) m_sorted[i] = 0;
    }

    static std::vector<T> filter(int size, const std::vector<T> &in) {
        std::vector<T> out;
        MedianFilter<T> f(size);
        for (int i = 0; i < int(in.size()); ++i) {
            f.push(in[i]);
            T median = f.get();
            if (i >= size/2) out.push_back(median);
        }
        while (out.size() < in.size()) {
            f.push(T());
            out.push_back(f.get());
        }
        return out;
    }

private:
    const int m_size;
    T *const m_frame;
    T *const m_sorted;
    T *const m_sortend;
    int m_index;

    void put(T value) {
	// precondition: m_sorted contains m_size-1 values, packed at start
	// postcondition: m_sorted contains m_size values, one of which is value
	T *point = std::lower_bound(m_sorted, m_sortend, value);
	const int n = m_sortend - point;
	for (int i = n; i > 0; --i) point[i] = point[i-1];
	*point = value;
    }

    void drop(T value) {
	// precondition: m_sorted contains m_size values, one of which is value
	// postcondition: m_sorted contains m_size-1 values, packed at start
	T *point = std::lower_bound(m_sorted, m_sortend + 1, value);
	if (*point != value) {
	    std::cerr << "WARNING: MedianFilter::drop: *point is " << *point
		      << ", expected " << value << std::endl;
	}
	const int n = m_sortend - point;
	for (int i = 0; i < n; ++i) point[i] = point[i+1];
	*m_sortend = T(0);
    }

    MedianFilter(const MedianFilter &); // not provided
    MedianFilter &operator=(const MedianFilter &); // not provided
};

#endif