vpHistogram.cpp

/*
 * ViSP, open source Visual Servoing Platform software.
 * Copyright (C) 2005 - 2024 by Inria. All rights reserved.
 *
 * This software 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 LICENSE.txt at the root directory of this source
 * distribution for additional information about the GNU GPL.
 *
 * For using ViSP with software that can not be combined with the GNU
 * GPL, please contact Inria about acquiring a ViSP Professional
 * Edition License.
 *
 * See https://visp.inria.fr for more information.
 *
 * This software was developed at:
 * Inria Rennes - Bretagne Atlantique
 * Campus Universitaire de Beaulieu
 * 35042 Rennes Cedex
 * France
 *
 * If you have questions regarding the use of this file, please contact
 * Inria at visp@inria.fr
 *
 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Description:
 * Gray level histogram manipulation.
 */

 
#include <stdlib.h>
#include <visp3/core/vpDisplay.h>
#include <visp3/core/vpHistogram.h>
#include <visp3/core/vpImageConvert.h>
 
BEGIN_VISP_NAMESPACE
const unsigned int vpHistogram::constr_val_256 = 256;
#if defined(VISP_HAVE_THREADS)
#ifndef DOXYGEN_SHOULD_SKIP_THIS
namespace
{
struct vpHistogram_Param_t
{
  unsigned int m_start_index;
  unsigned int m_end_index;
 
  unsigned int m_lut[256];
  unsigned int *m_histogram;
  const vpImage<unsigned char> *m_I;
  const vpImage<bool> *m_mask;
 
  vpHistogram_Param_t() : m_start_index(0), m_end_index(0), m_lut(), m_histogram(nullptr), m_I(nullptr), m_mask(nullptr) { }
 
  vpHistogram_Param_t(unsigned int start_index, unsigned int end_index, const vpImage<unsigned char> *const I, const vpImage<bool> *const mask)
    : m_start_index(start_index), m_end_index(end_index), m_lut(), m_histogram(nullptr), m_I(I), m_mask(mask)
  { }
 
  ~vpHistogram_Param_t()
  {
    if (m_histogram != nullptr) {
      delete[] m_histogram;
    }
  }
};
 
void computeHistogramThread(vpHistogram_Param_t *histogram_param)
{
  unsigned int start_index = histogram_param->m_start_index;
  unsigned int end_index = histogram_param->m_end_index;
 
  const vpImage<unsigned char> *I = histogram_param->m_I;
 
  unsigned char *ptrStart = (unsigned char *)(I->bitmap) + start_index;
  unsigned char *ptrEnd = (unsigned char *)(I->bitmap) + end_index;
  unsigned char *ptrCurrent = ptrStart;
 
  const bool alwaysTrue = true;
  const bool *ptrMaskCurrent = &alwaysTrue;
  if (histogram_param->m_mask) {
    ptrMaskCurrent = (const bool *)histogram_param->m_mask->bitmap + start_index;
  }
 
  if (end_index >= 8 + start_index) {
    // Unroll loop version
    for (; ptrCurrent <= ptrEnd - 8;) {
      if (*ptrMaskCurrent) {
        histogram_param->m_histogram[histogram_param->m_lut[*ptrCurrent]]++;
      }
      ++ptrCurrent;
      if (histogram_param->m_mask != nullptr) {
        ++ptrMaskCurrent;
      }
 
      if (*ptrMaskCurrent) {
        histogram_param->m_histogram[histogram_param->m_lut[*ptrCurrent]]++;
      }
      ++ptrCurrent;
      if (histogram_param->m_mask != nullptr) {
        ++ptrMaskCurrent;
      }
 
      if (*ptrMaskCurrent) {
        histogram_param->m_histogram[histogram_param->m_lut[*ptrCurrent]]++;
      }
      ++ptrCurrent;
      if (histogram_param->m_mask != nullptr) {
        ++ptrMaskCurrent;
      }
 
      if (*ptrMaskCurrent) {
        histogram_param->m_histogram[histogram_param->m_lut[*ptrCurrent]]++;
      }
      ++ptrCurrent;
      if (histogram_param->m_mask != nullptr) {
        ++ptrMaskCurrent;
      }
 
      if (*ptrMaskCurrent) {
        histogram_param->m_histogram[histogram_param->m_lut[*ptrCurrent]]++;
      }
      ++ptrCurrent;
      if (histogram_param->m_mask != nullptr) {
        ++ptrMaskCurrent;
      }
 
      if (*ptrMaskCurrent) {
        histogram_param->m_histogram[histogram_param->m_lut[*ptrCurrent]]++;
      }
      ++ptrCurrent;
      if (histogram_param->m_mask != nullptr) {
        ++ptrMaskCurrent;
      }
 
      if (*ptrMaskCurrent) {
        histogram_param->m_histogram[histogram_param->m_lut[*ptrCurrent]]++;
      }
      ++ptrCurrent;
      if (histogram_param->m_mask != nullptr) {
        ++ptrMaskCurrent;
      }
 
      if (*ptrMaskCurrent) {
        histogram_param->m_histogram[histogram_param->m_lut[*ptrCurrent]]++;
      }
      ++ptrCurrent;
      if (histogram_param->m_mask != nullptr) {
        ++ptrMaskCurrent;
      }
    }
  }
 
  for (; ptrCurrent != ptrEnd; ++ptrCurrent) {
    if (*ptrMaskCurrent) {
      histogram_param->m_histogram[histogram_param->m_lut[*ptrCurrent]]++;
    }
    if (histogram_param->m_mask != nullptr) {
      ++ptrMaskCurrent;
    }
  }
}
} // namespace
#endif // DOXYGEN_SHOULD_SKIP_THIS
#endif
 
bool compare_vpHistogramPeak(vpHistogramPeak first, vpHistogramPeak second);
 
// comparison,
bool compare_vpHistogramPeak(vpHistogramPeak first, vpHistogramPeak second)
{
  if (first.getValue() > second.getValue()) {
    return true;
  }
  else {
    return false;
  }
}

vpHistogram::vpHistogram(const unsigned int &size) : m_histogram(nullptr), m_size(size), mp_mask(nullptr), m_total(0) { init(size); }

vpHistogram::vpHistogram(const vpHistogram &h) : m_histogram(nullptr), m_size(constr_val_256), mp_mask(h.mp_mask), m_total(h.m_total)
{
  init(h.m_size);
  memcpy(m_histogram, h.m_histogram, m_size * sizeof(unsigned));
}

vpHistogram::vpHistogram(const vpImage<unsigned char> &I) : m_histogram(nullptr), m_size(constr_val_256), mp_mask(nullptr), m_total(0)
{
  init();
 
  calculate(I);
}

vpHistogram::vpHistogram(const vpImage<unsigned char> &I, const vpImage<bool> *p_mask) : m_histogram(nullptr), m_size(constr_val_256), mp_mask(nullptr), m_total(0)
{
  init();
  setMask(p_mask);
  calculate(I);
}

vpHistogram::~vpHistogram()
{
  if (m_histogram != nullptr) {
    delete[] m_histogram;
    m_histogram = nullptr;
    m_size = 0;
  }
}

vpHistogram &vpHistogram::operator=(const vpHistogram &h)
{
  init(h.m_size);
  memcpy(m_histogram, h.m_histogram, m_size * sizeof(unsigned));
  mp_mask = h.mp_mask;
  m_total = h.m_total;
 
  return *this;
}

void vpHistogram::init(unsigned size_)
{
  if (m_histogram != nullptr) {
    delete[] m_histogram;
    m_histogram = nullptr;
  }
 
  this->m_size = size_;
  m_histogram = new unsigned[m_size];
 
  memset(m_histogram, 0, m_size * sizeof(unsigned));
 
  mp_mask = nullptr;
  m_total = 0;
}

void vpHistogram::calculate(const vpImage<unsigned char> &I, unsigned int nbins, unsigned int nbThreads)
{
  const unsigned int val_256 = 256;
  if (m_size != nbins) {
    if (m_histogram != nullptr) {
      delete[] m_histogram;
      m_histogram = nullptr;
    }
 
    m_size = nbins > val_256 ? val_256 : (nbins > 0 ? nbins : val_256);
    if ((nbins > val_256) || (nbins == 0)) {
      std::cerr << "nbins=" << nbins << " , nbins should be between ]0 ; 256] ; use by default nbins=256" << std::endl;
    }
    m_histogram = new unsigned int[m_size];
  }
 
  memset(m_histogram, 0, m_size * sizeof(unsigned int));
 
  bool use_single_thread;
#if !defined(VISP_HAVE_THREADS)
  use_single_thread = true;
#else
  use_single_thread = (nbThreads == 0 || nbThreads == 1);
#endif
 
  if ((!use_single_thread) && (I.getSize() <= nbThreads)) {
    use_single_thread = true;
  }
 
  unsigned int lut[256];
  for (unsigned int i = 0; i < val_256; ++i) {
    lut[i] = static_cast<unsigned int>((i * m_size) / 256.0);
  }
 
  if (use_single_thread) {
    // Single thread
    const bool alwaysTrue = true;
    const bool *ptrMaskCurrent = &alwaysTrue;
    if (mp_mask) {
      ptrMaskCurrent = static_cast<const bool *>(mp_mask->bitmap);
    }
 
    unsigned int size_ = I.getWidth() * I.getHeight();
    unsigned char *ptrStart = static_cast<unsigned char *>(I.bitmap);
    unsigned char *ptrEnd = ptrStart + size_;
    unsigned char *ptrCurrent = ptrStart;
 
    m_total = 0;
    while (ptrCurrent != ptrEnd) {
      if (*ptrMaskCurrent) {
        ++m_histogram[lut[*ptrCurrent]];
        ++m_total;
      }
      ++ptrCurrent;
      if (mp_mask) {
        ++ptrMaskCurrent;
      }
    }
  }
  else {
#if defined(VISP_HAVE_THREADS)
    // Multi-threads
    std::vector<std::thread *> threadpool;
    std::vector<vpHistogram_Param_t *> histogramParams;
 
    unsigned int image_size = I.getSize();
    unsigned int step = image_size / nbThreads;
    unsigned int last_step = image_size - step * (nbThreads - 1);
 
    for (unsigned int index = 0; index < nbThreads; ++index) {
      unsigned int start_index = index * step;
      unsigned int end_index = (index + 1) * step;
 
      if (index == nbThreads - 1) {
        end_index = start_index + last_step;
      }
 
      vpHistogram_Param_t *histogram_param = new vpHistogram_Param_t(start_index, end_index, &I, mp_mask);
      histogram_param->m_histogram = new unsigned int[m_size];
      histogram_param->m_mask = mp_mask;
      memset(histogram_param->m_histogram, 0, m_size * sizeof(unsigned int));
      memcpy(histogram_param->m_lut, lut, 256 * sizeof(unsigned int));
 
      histogramParams.push_back(histogram_param);
 
      // Start the threads
      std::thread *histogram_thread = new std::thread(&computeHistogramThread, histogram_param);
      threadpool.push_back(histogram_thread);
    }
 
    for (size_t cpt = 0; cpt < threadpool.size(); ++cpt) {
      // Wait until thread ends up
      threadpool[cpt]->join();
    }
 
    m_total = 0;
    for (unsigned int cpt1 = 0; cpt1 < m_size; ++cpt1) {
      unsigned int sum = 0;
 
      for (size_t cpt2 = 0; cpt2 < histogramParams.size(); ++cpt2) {
        sum += histogramParams[cpt2]->m_histogram[cpt1];
      }
 
      m_histogram[cpt1] = sum;
      m_total += sum;
    }
 
    // Delete
    for (size_t cpt = 0; cpt < threadpool.size(); ++cpt) {
      delete threadpool[cpt];
    }
 
    for (size_t cpt = 0; cpt < histogramParams.size(); ++cpt) {
      delete histogramParams[cpt];
    }
#endif
  }
}
 
void vpHistogram::equalize(const vpImage<unsigned char> &I, vpImage<unsigned char> &Iout)
{
  // Compute the histogram
  calculate(I);
 
  // Calculate the cumulative distribution function
  unsigned int cdf[256];
  unsigned int cdfMin = std::numeric_limits<unsigned int>::max(), cdfMax = 0;
  unsigned int minValue = std::numeric_limits<unsigned int>::max(), maxValue = 0;
  cdf[0] = m_histogram[0];
 
  if ((cdf[0] < cdfMin) && (cdf[0] > 0)) {
    cdfMin = cdf[0];
    minValue = 0;
  }
 
  const unsigned int val_256 = 256;
  for (unsigned int i = 1; i < val_256; ++i) {
    cdf[i] = cdf[i - 1] + m_histogram[i];
 
    if ((cdf[i] < cdfMin) && (cdf[i] > 0)) {
      cdfMin = cdf[i];
      minValue = i;
    }
 
    if (cdf[i] > cdfMax) {
      cdfMax = cdf[i];
      maxValue = i;
    }
  }
 
  unsigned int nbPixels = I.getWidth() * I.getHeight();
  if (nbPixels == cdfMin) {
    // Only one brightness value in the image
    return;
  }
 
  // Construct the look-up table
  unsigned char lut[256];
  for (unsigned int x = minValue; x <= maxValue; ++x) {
    lut[x] = vpMath::round(((cdf[x] - cdfMin) / static_cast<double>(nbPixels - cdfMin)) * 255.0);
  }
 
  Iout = I;
  Iout.performLut(lut);
}

void vpHistogram::display(const vpImage<unsigned char> &I, const vpColor &color, unsigned int thickness,
                          unsigned int maxValue_)
{
  unsigned int width = I.getWidth(), height = I.getHeight();
  // Minimal width and height are 36 px
  if ((width < 36) || (height < 36)) {
    std::cerr << "Image I must have at least width >= 36 && height >= 36 !" << std::endl;
    return;
  }
 
  unsigned int maxValue = maxValue_;
  if (maxValue == 0) {
    for (unsigned int i = 0; i < m_size; ++i) {
      if (m_histogram[i] > maxValue) {
        maxValue = m_histogram[i];
      }
    }
  }
 
  if (maxValue == 0) {
    throw(vpException(vpException::divideByZeroError, "Cannot display histogram; max value=0"));
  }
  // Keep 12 free pixels at the top
  unsigned int max_height = height - 12;
  double ratio_height = max_height / static_cast<double>(maxValue);
  double ratio_width = (width - 1) / static_cast<double>(m_size - 1.0);
 
  for (unsigned int i = 1; i < m_size; ++i) {
    unsigned int value1 = m_histogram[i - 1];
    unsigned int value2 = m_histogram[i];
 
    vpImagePoint startPt((height - 1) - (value1 * ratio_height), (i - 1) * ratio_width);
    vpImagePoint endPt((height - 1) - (value2 * ratio_height), (i * ratio_width));
    vpDisplay::displayLine(I, startPt, endPt, color, thickness);
  }
}

void vpHistogram::smooth(unsigned int fsize)
{
  if (m_histogram == nullptr) {
    throw(vpImageException(vpImageException::notInitializedError, "Histogram array not initialised"));
  }
 
  vpHistogram h;
  h = *this;
 
  unsigned int hsize = fsize / 2; // half filter size
  unsigned int sizeAsInt = m_size;
 
  for (unsigned int i = 0; i < sizeAsInt; ++i) {
    unsigned int sum = 0;
    unsigned int nb = 0;
    for (unsigned int j = 0; j <= hsize; ++j) {
      // exploitation of the overflow to detect negative value...
      if ((i - j) < sizeAsInt) {
        sum += h.m_histogram[i - j];
        ++nb;
      }
      if ((i + j) < sizeAsInt) {
        sum += h.m_histogram[i + j];
        ++nb;
      }
    }
    m_histogram[i] = sum / nb;
  }
}

unsigned vpHistogram::getPeaks(std::list<vpHistogramPeak> &peaks)
{
  if (m_histogram == nullptr) {
    throw(vpImageException(vpImageException::notInitializedError, "Histogram array not initialised"));
  }
 
  int prev_slope;    // Previous histogram inclination
  vpHistogramPeak p; // An histogram peak
  unsigned nbpeaks;  // Number of peaks in the histogram (ie local maxima)
 
  peaks.clear();
 
  // Parse the histogram to get the local maxima
  unsigned cpt = 0;
  unsigned sum_level = 0;
  nbpeaks = 0;
  prev_slope = 1;
 
  for (unsigned i = 0; i < (m_size - 1); ++i) {
    int next_slope = static_cast<int>(m_histogram[i + 1]) - static_cast<int>(m_histogram[i]); // Next histogram inclination
 
    if ((prev_slope > 0) && (next_slope == 0)) {
      sum_level += i + 1;
      ++cpt;
    }
    else {
      // Peak detection
      if ((prev_slope > 0) && (next_slope < 0)) {
        sum_level += i;
        ++cpt;
 
        unsigned int level = sum_level / cpt;
        p.set(static_cast<unsigned char>(level), m_histogram[level]);
        peaks.push_back(p);
 
        ++nbpeaks;
      }
 
      prev_slope = next_slope;
      sum_level = 0;
      cpt = 0;
    }
  }
  if (prev_slope > 0) {
    p.set(static_cast<unsigned char>(m_size) - 1u, m_histogram[m_size - 1]);
    peaks.push_back(p);
    ++nbpeaks;
  }
 
  return nbpeaks;
}

unsigned vpHistogram::getPeaks(unsigned char dist, vpHistogramPeak &peak1, vpHistogramPeak &peak2)
{
  std::list<vpHistogramPeak> peaks;
  unsigned nbpeaks; // Number of peaks in the histogram (ie local maxima)
  const unsigned int val_2 = 2;
 
  nbpeaks = getPeaks(peaks);
  sort(peaks);
 
  if (nbpeaks == 0) {
    peak1.set(0, 0);
    peak2.set(0, 0);
    return 0;
  }
 
  if (nbpeaks == 1) {
    peak1 = peaks.front();
    peak2.set(0, 0);
    return 1;
  }
 
  // Parse the peaks list to get the peak with a distance greater
  // than dist to the highest
  peak1 = peaks.front();
  std::list<vpHistogramPeak>::const_iterator peaks_end = peaks.end();
  for (std::list<vpHistogramPeak>::const_iterator it = peaks.begin(); it != peaks_end; ++it) {
    vpHistogramPeak p = *it;
    if (abs(p.getLevel() - peak1.getLevel()) > dist) {
      // The second peak is found
      peak2 = p;
      return val_2;
    }
  }
 
  // No second peak found
  peak2.set(0, 0);
  return 1;
}

 
bool vpHistogram::getPeaks(unsigned char dist, vpHistogramPeak &peakl, vpHistogramPeak &peakr, vpHistogramValey &valey)
{
  unsigned char *peak;         // Local maxima values
  int prev_slope;              // Previous histogram inclination
  unsigned index_highest_peak; // Index in peak[] array of the highest peak
  unsigned index_second_peak;  // Index in peak[] array of the second peak
 
  unsigned int prof;
  unsigned int maxprof;    // Nb pixels difference between 2 maxi peaks
  unsigned int nbmini;     // Minimum numbers
  unsigned int sumindmini; // Sum
  unsigned int mini;       // current minimum
  unsigned int nbpeaks;    // Number of peaks in the histogram (ie local maxima)
 
  // Init the valey
  valey.set(0, 0);
 
  // Allocation for the
  peak = new unsigned char[m_size];
 
  // Parse the histogram to get the local maxima
  nbpeaks = 0;
  prev_slope = 1;
  for (unsigned i = 0; i < (m_size - 1); ++i) {
    int next_slope = static_cast<int>(m_histogram[i + 1]) - static_cast<int>(m_histogram[i]); // Next histogram inclination
    if (next_slope == 0) {
      // continue
    }
    else {
    // Peak detection
      if ((prev_slope > 0) && (next_slope < 0)) {
        peak[nbpeaks++] = static_cast<unsigned char>(i);
      }
 
      prev_slope = next_slope;
    }
  }
  if (prev_slope > 0) {
    peak[nbpeaks++] = static_cast<unsigned char>(m_size - 1);
  }
 
  // Get the global maximum
  index_highest_peak = 0;
  for (unsigned int i = 0; i < nbpeaks; ++i) {
    if (m_histogram[peak[i]] > m_histogram[peak[index_highest_peak]]) {
      index_highest_peak = i;
    }
  }
 
  maxprof = 0;
  index_second_peak = index_highest_peak;
 
  // Search second local maximum on the left of the global maximum
  for (unsigned i = 0; i < index_highest_peak; ++i) {
    if ((peak[index_highest_peak] - peak[i]) > dist) {
      prof = 0;
      for (int j = peak[i]; j <= (peak[index_highest_peak] - dist); ++j) {
        if ((m_histogram[peak[i]] - m_histogram[j]) > prof) {
          prof = m_histogram[peak[i]] - m_histogram[j];
        }
      }
 
      if (prof > maxprof) {
        maxprof = prof;
        index_second_peak = i;
      }
    }
  }
 
  // Search second local maximum on the right of the global maximum
  for (unsigned i = index_highest_peak + 1; i < nbpeaks; ++i) {
    if ((peak[i] - peak[index_highest_peak]) > dist) {
      prof = 0;
      for (int j = peak[index_highest_peak] + dist; j <= peak[i]; ++j) {
        if ((m_histogram[peak[i]] - m_histogram[j]) > prof) {
          prof = m_histogram[peak[i]] - m_histogram[j];
        }
      }
 
      if (prof > maxprof) {
        maxprof = prof;
        index_second_peak = i;
      }
    }
  }
 
  // Determine position of the first and second highest peaks
  if (peak[index_highest_peak] < peak[index_second_peak]) {
    peakr.set(peak[index_second_peak], m_histogram[peak[index_second_peak]]);
    peakl.set(peak[index_highest_peak], m_histogram[peak[index_highest_peak]]);
  }
  else {
    peakl.set(peak[index_second_peak], m_histogram[peak[index_second_peak]]);
    peakr.set(peak[index_highest_peak], m_histogram[peak[index_highest_peak]]);
  }
 
  if (peakl == peakr) {
 
    delete[] peak;
 
    return false; // Not a bimodal histogram
  }
 
  // Search the valey
  mini = peakl.getValue();
  sumindmini = 0;
  nbmini = 0;
  unsigned peakr_level = peakr.getLevel();
  for (unsigned i = peakl.getLevel(); i <= peakr_level; ++i) {
    if (m_histogram[i] < mini) {
      mini = m_histogram[i];
      nbmini = 1;
      sumindmini = i;
      // continue
    }
    else {
      if (m_histogram[i] == mini) {
        sumindmini += i;
        ++nbmini;
      }
    }
  }
 
  if (nbmini == 0) {
    // no valey found
    valey.set(0, 0);
 
    delete[] peak;
 
    return false;
  }
  else {
    mini = sumindmini / nbmini; // mean
    valey.set(static_cast<unsigned char>(mini), m_histogram[mini]);
 
    delete[] peak;
 
    return true;
  }
}

unsigned vpHistogram::getValey(std::list<vpHistogramValey> &valey)
{
  if (m_histogram == nullptr) {
    throw(vpImageException(vpImageException::notInitializedError, "Histogram array not initialised"));
  }
 
  int prev_slope;     // Previous histogram inclination
  vpHistogramValey p; // An histogram valey
  unsigned nbvaley;   // Number of valey in the histogram (ie local minima)
 
  valey.clear();
 
  // Parse the histogram to get the local minima
  unsigned cpt = 0;
  unsigned sum_level = 0;
  nbvaley = 0;
  prev_slope = -1;
 
  for (unsigned i = 0; i < (m_size - 1); ++i) {
    int next_slope = static_cast<int>(m_histogram[i + 1]) - static_cast<int>(m_histogram[i]); // Next histogram inclination
 
    if ((prev_slope < 0) && (next_slope == 0)) {
      sum_level += i + 1;
      ++cpt;
      // continue
    }
    else {
    // Valey detection
      if ((prev_slope < 0) && (next_slope > 0)) {
        sum_level += i;
        ++cpt;
 
        unsigned int level = sum_level / cpt;
        p.set(static_cast<unsigned char>(level), m_histogram[level]);
        valey.push_back(p);
 
        ++nbvaley;
      }
 
      prev_slope = next_slope;
      sum_level = 0;
      cpt = 0;
    }
  }
  if (prev_slope < 0) {
    p.set(static_cast<unsigned char>(m_size) - 1u, m_histogram[m_size - 1]);
    valey.push_back(p);
    ++nbvaley;
  }
 
  return nbvaley;
}

bool vpHistogram::getValey(const vpHistogramPeak &peak1, const vpHistogramPeak &peak2, vpHistogramValey &valey)
{
 
  // Set the left and right peaks
  vpHistogramPeak peakl, peakr;
  if (peak1.getLevel() > peak2.getLevel()) {
    peakl = peak2;
    peakr = peak1;
  }
  else {
    peakl = peak1;
    peakr = peak2;
  }
 
  // Search the valey
  unsigned int nbmini;     // Minimum numbers
  unsigned int sumindmini; // Sum
  unsigned int mini;       // current minimum
 
  mini = peakl.getValue();
  sumindmini = 0;
  nbmini = 0;
  unsigned peakr_level = peakr.getLevel();
  for (unsigned i = peakl.getLevel(); i <= peakr_level; ++i) {
    if (m_histogram[i] < mini) {
      mini = m_histogram[i];
      nbmini = 1;
      sumindmini = i;
      // continue
    }
    else {
      if (m_histogram[i] == mini) {
        sumindmini += i;
        ++nbmini;
      }
    }
  }
 
  if (nbmini == 0) {
    // no valey found
    valey.set(0, 0);
 
    return false;
  }
  else {
    unsigned int minipos = sumindmini / nbmini; // position of the minimum
 
    valey.set(static_cast<unsigned char>(minipos), m_histogram[minipos]);
    return true;
  }
}

unsigned vpHistogram::getValey(unsigned char dist, const vpHistogramPeak &peak, vpHistogramValey &valeyl,
                               vpHistogramValey &valeyr)
{
  const unsigned int val_ui_0x10 = 0x10;
  const unsigned int val_ui_0x11 = 0x11;
  unsigned int ret = 0x11;
  unsigned int nbmini;              // Minimum numbers
  unsigned int sumindmini;          // Sum
  unsigned int mini;                // current minimum
  vpHistogramPeak peakr, peakl;     // Left and right peaks of peak
  std::list<vpHistogramPeak> peaks; // list of histogram peaks
  //   unsigned int nbpeaks=0; // Number of peaks in the histogram (ie local
  //   maxima)
 
  if (peak.getLevel() == 0) {
    valeyl.set(0, 0);
    ret &= 0x01;
  }
  if (peak.getLevel() == (m_size - 1)) {
    valeyr.set(static_cast<unsigned char>(m_size - 1), 0);
    ret &= val_ui_0x10;
  }
 
  if (ret >> 1) // consider the left part of the requested peak
  {
    // If the list of peaks is empty, compute it
    if (peaks.empty()) {
      /* nbpeaks = */ getPeaks(peaks);
    }
 
    // Go to the requested peak in the list
    std::list<vpHistogramPeak>::const_iterator it;
    unsigned index = 0;
    std::list<vpHistogramPeak>::const_iterator peaks_end = peaks.end();
    for (it = peaks.begin(); it != peaks_end; ++it) {
      if (peak == *it) {
        // we are on the peak.
        break;
      }
      ++index;
    }
 
    bool found = false;
    if (index == 0) {
      // No chance to get a peak on the left
      // should not occur !
      peakl.set(0, 0);
    }
    else {
      // search for the nearest peak on the left that matches the distance
      std::list<vpHistogramPeak>::const_iterator lit; // left iterator
      for (lit = peaks.begin(); lit != it; ++lit) {
        if (abs((*lit).getLevel() - peak.getLevel()) > dist) {
          // peakl found
          peakl = *lit;
          found = true; // we cannot stop here, since the other peaks on the
          // right may exist
        }
      }
    }
    if (!found) {
      peakl.set(0, 0);
    }
 
    // Search the valey on the left
    mini = peak.getValue();
    sumindmini = 0;
    nbmini = 0;
    unsigned peak_level = peak.getLevel();
    for (unsigned i = peakl.getLevel(); i < peak_level; ++i) {
      if (m_histogram[i] < mini) {
        mini = m_histogram[i];
        nbmini = 1;
        sumindmini = i;
        // continue
      }
      else {
        if (m_histogram[i] == mini) {
          sumindmini += i;
          ++nbmini;
        }
      }
    }
    if (nbmini == 0) {
      valeyl.set(0, 0);
      ret &= 0x01;
    }
    else {
      unsigned int minipos = sumindmini / nbmini; // position of the minimum
      valeyl.set(static_cast<unsigned char>(minipos), m_histogram[minipos]);
      ret &= val_ui_0x11;
    }
  }
 
  if (ret << 1) {
    // If the list of peaks is empty, compute it
    if (peaks.empty()) {
      /* nbpeaks = */ getPeaks(peaks);
    }
    // Go to the requested peak in the list
    std::list<vpHistogramPeak>::const_iterator it;
    std::list<vpHistogramPeak>::const_iterator peaks_end = peaks.end();
    for (it = peaks.begin(); it != peaks_end; ++it) {
      if (peak == *it) {
        // we are on the peak.
        break;
      }
    }
 
    bool found = false;
    // search for the nearest peak on the right that matches the distance
    std::list<vpHistogramPeak>::const_iterator rit; // right iterator
    std::list<vpHistogramPeak>::const_iterator peaks_end_s = peaks.end();
    for (rit = it; rit != peaks_end_s; ++rit) {
 
      if (abs((*rit).getLevel() - peak.getLevel()) > dist) {
        // peakr found
        peakr = *rit;
        found = true;
        break; // we can stop here
      }
    }
 
    if (!found) {
      peakr.set(static_cast<unsigned char>(m_size - 1), 0);
    }
 
    // Search the valey on the right
    mini = peak.getValue();
    sumindmini = 0;
    nbmini = 0;
    unsigned int peakr_level = static_cast<unsigned int>(peakr.getLevel());
    for (unsigned i = static_cast<unsigned int>(peak.getLevel()) + 1; i <= peakr_level; ++i) {
      if (m_histogram[i] < mini) {
        mini = m_histogram[i];
        nbmini = 1;
        sumindmini = i;
        // continue
      }
      else {
        if (m_histogram[i] == mini) {
          sumindmini += i;
          ++nbmini;
        }
      }
    }
    if (nbmini == 0) {
      valeyr.set(static_cast<unsigned char>(m_size - 1), 0);
      ret &= val_ui_0x10;
    }
    else {
      unsigned int minipos = sumindmini / nbmini; // position of the minimum
      valeyr.set(static_cast<unsigned char>(minipos), m_histogram[minipos]);
      ret &= val_ui_0x11;
    }
  }
 
  return ret;
}

unsigned vpHistogram::sort(std::list<vpHistogramPeak> &peaks)
{
 
  if (peaks.empty()) {
    return 0;
  }
 
  peaks.sort(compare_vpHistogramPeak);
 
  return static_cast<unsigned int>(peaks.size());
}

 
bool vpHistogram::write(const std::string &filename) { return (this->write(filename.c_str())); }

 
bool vpHistogram::write(const char *filename)
{
  FILE *fd = fopen(filename, "w");
  if (fd == nullptr) {
    return false;
  }
  for (unsigned i = 0; i < m_size; ++i) {
    fprintf(fd, "%u %u\n", i, m_histogram[i]);
  }
  fclose(fd);
 
  return true;
}
END_VISP_NAMESPACE