added felzenszwalb code

COPYING

@@ -0,0 +1,339 @@
+		    GNU GENERAL PUBLIC LICENSE
+		       Version 2, June 1991
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+Public License instead of this License.

Makefile

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+INCDIR = -I.
+DBG    = -g
+OPT    = -O3
+CPP    = g++
+CFLAGS = $(DBG) $(OPT) $(INCDIR)
+LINK   = -lm 
+
+.cpp.o:
+	$(CPP) $(CFLAGS) -c $< -o $@
+
+all: segment
+
+segment: segment.cpp segment-image.h segment-graph.h disjoint-set.h
+	$(CPP) $(CFLAGS) -o segment segment.cpp $(LINK)
+
+clean:
+	/bin/rm -f segment *.o
+
+clean-all: clean
+	/bin/rm -f *~ 
+
+
+

README

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+
+Implementation of the segmentation algorithm described in:
+
+Efficient Graph-Based Image Segmentation
+Pedro F. Felzenszwalb and Daniel P. Huttenlocher
+International Journal of Computer Vision, 59(2) September 2004.
+
+The program takes a color image (PPM format) and produces a segmentation
+with a random color assigned to each region.
+
+1) Type "make" to compile "segment".
+
+2) Run "segment sigma k min input output".
+
+The parameters are: (see the paper for details)
+
+sigma: Used to smooth the input image before segmenting it.
+k: Value for the threshold function.
+min: Minimum component size enforced by post-processing.
+input: Input image.
+output: Output image.
+
+Typical parameters are sigma = 0.5, k = 500, min = 20.
+Larger values for k result in larger components in the result.
+

convolve.h

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+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+/* convolution */
+
+#ifndef CONVOLVE_H
+#define CONVOLVE_H
+
+#include <vector>
+#include <algorithm>
+#include <cmath>
+#include "image.h"
+
+/* convolve src with mask.  dst is flipped! */
+static void convolve_even(image<float> *src, image<float> *dst, 
+			  std::vector<float> &mask) {
+  int width = src->width();
+  int height = src->height();
+  int len = mask.size();
+
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      float sum = mask[0] * imRef(src, x, y);
+      for (int i = 1; i < len; i++) {
+	sum += mask[i] * 
+	  (imRef(src, std::max(x-i,0), y) + 
+	   imRef(src, std::min(x+i, width-1), y));
+      }
+      imRef(dst, y, x) = sum;
+    }
+  }
+}
+
+/* convolve src with mask.  dst is flipped! */
+static void convolve_odd(image<float> *src, image<float> *dst, 
+			 std::vector<float> &mask) {
+  int width = src->width();
+  int height = src->height();
+  int len = mask.size();
+
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      float sum = mask[0] * imRef(src, x, y);
+      for (int i = 1; i < len; i++) {
+	sum += mask[i] * 
+	  (imRef(src, std::max(x-i,0), y) - 
+	   imRef(src, std::min(x+i, width-1), y));
+      }
+      imRef(dst, y, x) = sum;
+    }
+  }
+}
+
+#endif

disjoint-set.h

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+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+#ifndef DISJOINT_SET
+#define DISJOINT_SET
+
+// disjoint-set forests using union-by-rank and path compression (sort of).
+
+typedef struct {
+  int rank;
+  int p;
+  int size;
+} uni_elt;
+
+class universe {
+public:
+  universe(int elements);
+  ~universe();
+  int find(int x);  
+  void join(int x, int y);
+  int size(int x) const { return elts[x].size; }
+  int num_sets() const { return num; }
+
+private:
+  uni_elt *elts;
+  int num;
+};
+
+universe::universe(int elements) {
+  elts = new uni_elt[elements];
+  num = elements;
+  for (int i = 0; i < elements; i++) {
+    elts[i].rank = 0;
+    elts[i].size = 1;
+    elts[i].p = i;
+  }
+}
+  
+universe::~universe() {
+  delete [] elts;
+}
+
+int universe::find(int x) {
+  int y = x;
+  while (y != elts[y].p)
+    y = elts[y].p;
+  elts[x].p = y;
+  return y;
+}
+
+void universe::join(int x, int y) {
+  if (elts[x].rank > elts[y].rank) {
+    elts[y].p = x;
+    elts[x].size += elts[y].size;
+  } else {
+    elts[x].p = y;
+    elts[y].size += elts[x].size;
+    if (elts[x].rank == elts[y].rank)
+      elts[y].rank++;
+  }
+  num--;
+}
+
+#endif

filter.h

@@ -0,0 +1,100 @@
+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+/* simple filters */
+
+#ifndef FILTER_H
+#define FILTER_H
+
+#include <vector>
+#include <cmath>
+#include "image.h"
+#include "misc.h"
+#include "convolve.h"
+#include "imconv.h"
+
+#define WIDTH 4.0
+
+/* normalize mask so it integrates to one */
+static void normalize(std::vector<float> &mask) {
+  int len = mask.size();
+  float sum = 0;
+  for (int i = 1; i < len; i++) {
+    sum += fabs(mask[i]);
+  }
+  sum = 2*sum + fabs(mask[0]);
+  for (int i = 0; i < len; i++) {
+    mask[i] /= sum;
+  }
+}
+
+/* make filters */
+#define MAKE_FILTER(name, fun)                                \
+static std::vector<float> make_ ## name (float sigma) {       \
+  sigma = std::max(sigma, 0.01F);			      \
+  int len = (int)ceil(sigma * WIDTH) + 1;                     \
+  std::vector<float> mask(len);                               \
+  for (int i = 0; i < len; i++) {                             \
+    mask[i] = fun;                                            \
+  }                                                           \
+  return mask;                                                \
+}
+
+MAKE_FILTER(fgauss, exp(-0.5*square(i/sigma)));
+
+/* convolve image with gaussian filter */
+static image<float> *smooth(image<float> *src, float sigma) {
+  std::vector<float> mask = make_fgauss(sigma);
+  normalize(mask);
+
+  image<float> *tmp = new image<float>(src->height(), src->width(), false);
+  image<float> *dst = new image<float>(src->width(), src->height(), false);
+  convolve_even(src, tmp, mask);
+  convolve_even(tmp, dst, mask);
+
+  delete tmp;
+  return dst;
+}
+
+/* convolve image with gaussian filter */
+image<float> *smooth(image<uchar> *src, float sigma) {
+  image<float> *tmp = imageUCHARtoFLOAT(src);
+  image<float> *dst = smooth(tmp, sigma);
+  delete tmp;
+  return dst;
+}
+
+/* compute laplacian */
+static image<float> *laplacian(image<float> *src) {
+  int width = src->width();
+  int height = src->height();
+  image<float> *dst = new image<float>(width, height);  
+
+  for (int y = 1; y < height-1; y++) {
+    for (int x = 1; x < width-1; x++) {
+      float d2x = imRef(src, x-1, y) + imRef(src, x+1, y) -
+	2*imRef(src, x, y);
+      float d2y = imRef(src, x, y-1) + imRef(src, x, y+1) -
+	2*imRef(src, x, y);
+      imRef(dst, x, y) = d2x + d2y;
+    }
+  }
+  return dst;
+}
+
+#endif

image.h

@@ -0,0 +1,101 @@
+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+/* a simple image class */
+
+#ifndef IMAGE_H
+#define IMAGE_H
+
+#include <cstring>
+
+template <class T>
+class image {
+ public:
+  /* create an image */
+  image(const int width, const int height, const bool init = true);
+
+  /* delete an image */
+  ~image();
+
+  /* init an image */
+  void init(const T &val);
+
+  /* copy an image */
+  image<T> *copy() const;
+  
+  /* get the width of an image. */
+  int width() const { return w; }
+  
+  /* get the height of an image. */
+  int height() const { return h; }
+  
+  /* image data. */
+  T *data;
+  
+  /* row pointers. */
+  T **access;
+  
+ private:
+  int w, h;
+};
+
+/* use imRef to access image data. */
+#define imRef(im, x, y) (im->access[y][x])
+  
+/* use imPtr to get pointer to image data. */
+#define imPtr(im, x, y) &(im->access[y][x])
+
+template <class T>
+image<T>::image(const int width, const int height, const bool init) {
+  w = width;
+  h = height;
+  data = new T[w * h];  // allocate space for image data
+  access = new T*[h];   // allocate space for row pointers
+  
+  // initialize row pointers
+  for (int i = 0; i < h; i++)
+    access[i] = data + (i * w);  
+  
+  if (init)
+    memset(data, 0, w * h * sizeof(T));
+}
+
+template <class T>
+image<T>::~image() {
+  delete [] data; 
+  delete [] access;
+}
+
+template <class T>
+void image<T>::init(const T &val) {
+  T *ptr = imPtr(this, 0, 0);
+  T *end = imPtr(this, w-1, h-1);
+  while (ptr <= end)
+    *ptr++ = val;
+}
+
+
+template <class T>
+image<T> *image<T>::copy() const {
+  image<T> *im = new image<T>(w, h, false);
+  memcpy(im->data, data, w * h * sizeof(T));
+  return im;
+}
+
+#endif
+  

imconv.h

@@ -0,0 +1,177 @@
+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+/* image conversion */
+
+#ifndef CONV_H
+#define CONV_H
+
+#include <climits>
+#include "image.h"
+#include "imutil.h"
+#include "misc.h"
+
+#define	RED_WEIGHT	0.299
+#define GREEN_WEIGHT	0.587
+#define BLUE_WEIGHT	0.114
+
+static image<uchar> *imageRGBtoGRAY(image<rgb> *input) {
+  int width = input->width();
+  int height = input->height();
+  image<uchar> *output = new image<uchar>(width, height, false);
+
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      imRef(output, x, y) = (uchar)
+	(imRef(input, x, y).r * RED_WEIGHT +
+	 imRef(input, x, y).g * GREEN_WEIGHT +
+	 imRef(input, x, y).b * BLUE_WEIGHT);
+    }
+  }
+  return output;
+}
+
+static image<rgb> *imageGRAYtoRGB(image<uchar> *input) {
+  int width = input->width();
+  int height = input->height();
+  image<rgb> *output = new image<rgb>(width, height, false);
+
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      imRef(output, x, y).r = imRef(input, x, y);
+      imRef(output, x, y).g = imRef(input, x, y);
+      imRef(output, x, y).b = imRef(input, x, y);
+    }
+  }
+  return output;  
+}
+
+static image<float> *imageUCHARtoFLOAT(image<uchar> *input) {
+  int width = input->width();
+  int height = input->height();
+  image<float> *output = new image<float>(width, height, false);
+
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      imRef(output, x, y) = imRef(input, x, y);
+    }
+  }
+  return output;  
+}
+
+static image<float> *imageINTtoFLOAT(image<int> *input) {
+  int width = input->width();
+  int height = input->height();
+  image<float> *output = new image<float>(width, height, false);
+
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      imRef(output, x, y) = imRef(input, x, y);
+    }
+  }
+  return output;  
+}
+
+static image<uchar> *imageFLOATtoUCHAR(image<float> *input, 
+				       float min, float max) {
+  int width = input->width();
+  int height = input->height();
+  image<uchar> *output = new image<uchar>(width, height, false);
+
+  if (max == min)
+    return output;
+
+  float scale = UCHAR_MAX / (max - min);
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      uchar val = (uchar)((imRef(input, x, y) - min) * scale);
+      imRef(output, x, y) = bound(val, (uchar)0, (uchar)UCHAR_MAX);
+    }
+  }
+  return output;
+}
+
+static image<uchar> *imageFLOATtoUCHAR(image<float> *input) {
+  float min, max;
+  min_max(input, &min, &max);
+  return imageFLOATtoUCHAR(input, min, max);
+}
+
+static image<long> *imageUCHARtoLONG(image<uchar> *input) {
+  int width = input->width();
+  int height = input->height();
+  image<long> *output = new image<long>(width, height, false);
+
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      imRef(output, x, y) = imRef(input, x, y);
+    }
+  }
+  return output;  
+}
+
+static image<uchar> *imageLONGtoUCHAR(image<long> *input, long min, long max) {
+  int width = input->width();
+  int height = input->height();
+  image<uchar> *output = new image<uchar>(width, height, false);
+
+  if (max == min)
+    return output;
+
+  float scale = UCHAR_MAX / (float)(max - min);
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      uchar val = (uchar)((imRef(input, x, y) - min) * scale);
+      imRef(output, x, y) = bound(val, (uchar)0, (uchar)UCHAR_MAX);
+    }
+  }
+  return output;
+}
+
+static image<uchar> *imageLONGtoUCHAR(image<long> *input) {
+  long min, max;
+  min_max(input, &min, &max);
+  return imageLONGtoUCHAR(input, min, max);
+}
+
+static image<uchar> *imageSHORTtoUCHAR(image<short> *input, 
+					short min, short max) {
+  int width = input->width();
+  int height = input->height();
+  image<uchar> *output = new image<uchar>(width, height, false);
+
+  if (max == min)
+    return output;
+
+  float scale = UCHAR_MAX / (float)(max - min);
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      uchar val = (uchar)((imRef(input, x, y) - min) * scale);
+      imRef(output, x, y) = bound(val, (uchar)0, (uchar)UCHAR_MAX);
+    }
+  }
+  return output;
+}
+
+static image<uchar> *imageSHORTtoUCHAR(image<short> *input) {
+  short min, max;
+  min_max(input, &min, &max);
+  return imageSHORTtoUCHAR(input, min, max);
+}
+
+#endif

imutil.h

@@ -0,0 +1,66 @@
+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+/* some image utilities */
+
+#ifndef IMUTIL_H
+#define IMUTIL_H
+
+#include "image.h"
+#include "misc.h"
+
+/* compute minimum and maximum value in an image */
+template <class T>
+void min_max(image<T> *im, T *ret_min, T *ret_max) {
+  int width = im->width();
+  int height = im->height();
+  
+  T min = imRef(im, 0, 0);
+  T max = imRef(im, 0, 0);
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      T val = imRef(im, x, y);
+      if (min > val)
+	min = val;
+      if (max < val)
+	max = val;
+    }
+  }
+
+  *ret_min = min;
+  *ret_max = max;
+} 
+
+/* threshold image */
+template <class T>
+image<uchar> *threshold(image<T> *src, int t) {
+  int width = src->width();
+  int height = src->height();
+  image<uchar> *dst = new image<uchar>(width, height);
+  
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      imRef(dst, x, y) = (imRef(src, x, y) >= t);
+    }
+  }
+
+  return dst;
+}
+
+#endif
+

misc.h

@@ -0,0 +1,65 @@
+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+/* random stuff */
+
+#ifndef MISC_H
+#define MISC_H
+
+#include <cmath>
+
+#ifndef M_PI
+#define M_PI 3.141592653589793
+#endif
+
+typedef unsigned char uchar;
+
+typedef struct { uchar r, g, b; } rgb;
+
+inline bool operator==(const rgb &a, const rgb &b) {
+  return ((a.r == b.r) && (a.g == b.g) && (a.b == b.b));
+}
+
+template <class T>
+inline T abs(const T &x) { return (x > 0 ? x : -x); };
+
+template <class T>
+inline int sign(const T &x) { return (x >= 0 ? 1 : -1); };
+
+template <class T>
+inline T square(const T &x) { return x*x; };
+
+template <class T>
+inline T bound(const T &x, const T &min, const T &max) {
+  return (x < min ? min : (x > max ? max : x));
+}
+
+template <class T>
+inline bool check_bound(const T &x, const T&min, const T &max) {
+  return ((x < min) || (x > max));
+}
+
+inline int vlib_round(float x) { return (int)(x + 0.5F); }
+
+inline int vlib_round(double x) { return (int)(x + 0.5); }
+
+inline double gaussian(double val, double sigma) {
+  return exp(-square(val/sigma)/2)/(sqrt(2*M_PI)*sigma);
+}
+
+#endif

pnmfile.h

@@ -0,0 +1,211 @@
+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+/* basic image I/O */
+
+#ifndef PNM_FILE_H
+#define PNM_FILE_H
+
+#include <cstdlib>
+#include <climits>
+#include <cstring>
+#include <fstream>
+#include "image.h"
+#include "misc.h"
+
+#define BUF_SIZE 256
+
+class pnm_error { };
+
+static void read_packed(unsigned char *data, int size, std::ifstream &f) {
+  unsigned char c = 0;
+  
+  int bitshift = -1;
+  for (int pos = 0; pos < size; pos++) {
+    if (bitshift == -1) {
+      c = f.get();
+      bitshift = 7;
+    }
+    data[pos] = (c >> bitshift) & 1;
+    bitshift--;
+    }
+}
+
+static void write_packed(unsigned char *data, int size, std::ofstream &f) {
+  unsigned char c = 0;
+  
+  int bitshift = 7;
+  for (int pos = 0; pos < size; pos++) {
+      c = c | (data[pos] << bitshift);
+      bitshift--;
+      if ((bitshift == -1) || (pos == size-1)) {
+	f.put(c);
+	bitshift = 7;
+	c = 0;
+      }
+  }
+}
+
+/* read PNM field, skipping comments */ 
+static void pnm_read(std::ifstream &file, char *buf) {
+  char doc[BUF_SIZE];
+  char c;
+  
+  file >> c;
+  while (c == '#') {
+    file.getline(doc, BUF_SIZE);
+    file >> c;
+  }
+  file.putback(c);
+  
+  file.width(BUF_SIZE);
+  file >> buf;
+  file.ignore();
+}
+
+static image<uchar> *loadPBM(const char *name) {
+  char buf[BUF_SIZE];
+  
+  /* read header */
+  std::ifstream file(name, std::ios::in | std::ios::binary);
+  pnm_read(file, buf);
+  if (strncmp(buf, "P4", 2))
+    throw pnm_error();
+    
+  pnm_read(file, buf);
+  int width = atoi(buf);
+  pnm_read(file, buf);
+  int height = atoi(buf);
+  
+  /* read data */
+  image<uchar> *im = new image<uchar>(width, height);
+  for (int i = 0; i < height; i++)
+    read_packed(imPtr(im, 0, i), width, file);
+  
+  return im;
+}
+
+static void savePBM(image<uchar> *im, const char *name) {
+  int width = im->width();
+  int height = im->height();
+  std::ofstream file(name, std::ios::out | std::ios::binary);
+
+  file << "P4\n" << width << " " << height << "\n";
+  for (int i = 0; i < height; i++)
+    write_packed(imPtr(im, 0, i), width, file);
+}
+
+static image<uchar> *loadPGM(const char *name) {
+  char buf[BUF_SIZE];
+  
+  /* read header */
+  std::ifstream file(name, std::ios::in | std::ios::binary);
+  pnm_read(file, buf);
+  if (strncmp(buf, "P5", 2))
+    throw pnm_error();
+
+  pnm_read(file, buf);
+  int width = atoi(buf);
+  pnm_read(file, buf);
+  int height = atoi(buf);
+
+  pnm_read(file, buf);
+  if (atoi(buf) > UCHAR_MAX)
+    throw pnm_error();
+
+  /* read data */
+  image<uchar> *im = new image<uchar>(width, height);
+  file.read((char *)imPtr(im, 0, 0), width * height * sizeof(uchar));
+
+  return im;
+}
+
+static void savePGM(image<uchar> *im, const char *name) {
+  int width = im->width();
+  int height = im->height();
+  std::ofstream file(name, std::ios::out | std::ios::binary);
+
+  file << "P5\n" << width << " " << height << "\n" << UCHAR_MAX << "\n";
+  file.write((char *)imPtr(im, 0, 0), width * height * sizeof(uchar));
+}
+
+static image<rgb> *loadPPM(const char *name) {
+  char buf[BUF_SIZE], doc[BUF_SIZE];
+  
+  /* read header */
+  std::ifstream file(name, std::ios::in | std::ios::binary);
+  pnm_read(file, buf);
+  if (strncmp(buf, "P6", 2))
+    throw pnm_error();
+
+  pnm_read(file, buf);
+  int width = atoi(buf);
+  pnm_read(file, buf);
+  int height = atoi(buf);
+
+  pnm_read(file, buf);
+  if (atoi(buf) > UCHAR_MAX)
+    throw pnm_error();
+
+  /* read data */
+  image<rgb> *im = new image<rgb>(width, height);
+  file.read((char *)imPtr(im, 0, 0), width * height * sizeof(rgb));
+
+  return im;
+}
+
+static void savePPM(image<rgb> *im, const char *name) {
+  int width = im->width();
+  int height = im->height();
+  std::ofstream file(name, std::ios::out | std::ios::binary);
+
+  file << "P6\n" << width << " " << height << "\n" << UCHAR_MAX << "\n";
+  file.write((char *)imPtr(im, 0, 0), width * height * sizeof(rgb));
+}
+
+template <class T>
+void load_image(image<T> **im, const char *name) {
+  char buf[BUF_SIZE];
+  
+  /* read header */
+  std::ifstream file(name, std::ios::in | std::ios::binary);
+  pnm_read(file, buf);
+  if (strncmp(buf, "VLIB", 9))
+    throw pnm_error();
+
+  pnm_read(file, buf);
+  int width = atoi(buf);
+  pnm_read(file, buf);
+  int height = atoi(buf);
+
+  /* read data */
+  *im = new image<T>(width, height);
+  file.read((char *)imPtr((*im), 0, 0), width * height * sizeof(T));
+}
+
+template <class T>
+void save_image(image<T> *im, const char *name) {
+  int width = im->width();
+  int height = im->height();
+  std::ofstream file(name, std::ios::out | std::ios::binary);
+
+  file << "VLIB\n" << width << " " << height << "\n";
+  file.write((char *)imPtr(im, 0, 0), width * height * sizeof(T));
+}
+
+#endif

segment-graph.h

@@ -0,0 +1,83 @@
+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+#ifndef SEGMENT_GRAPH
+#define SEGMENT_GRAPH
+
+#include <algorithm>
+#include <cmath>
+#include "disjoint-set.h"
+
+// threshold function
+#define THRESHOLD(size, c) (c/size)
+
+typedef struct {
+  float w;
+  int a, b;
+} edge;
+
+bool operator<(const edge &a, const edge &b) {
+  return a.w < b.w;
+}
+
+/*
+ * Segment a graph
+ *
+ * Returns a disjoint-set forest representing the segmentation.
+ *
+ * num_vertices: number of vertices in graph.
+ * num_edges: number of edges in graph
+ * edges: array of edges.
+ * c: constant for treshold function.
+ */
+universe *segment_graph(int num_vertices, int num_edges, edge *edges, 
+			float c) { 
+  // sort edges by weight
+  std::sort(edges, edges + num_edges);
+
+  // make a disjoint-set forest
+  universe *u = new universe(num_vertices);
+
+  // init thresholds
+  float *threshold = new float[num_vertices];
+  for (int i = 0; i < num_vertices; i++)
+    threshold[i] = THRESHOLD(1,c);
+
+  // for each edge, in non-decreasing weight order...
+  for (int i = 0; i < num_edges; i++) {
+    edge *pedge = &edges[i];
+    
+    // components conected by this edge
+    int a = u->find(pedge->a);
+    int b = u->find(pedge->b);
+    if (a != b) {
+      if ((pedge->w <= threshold[a]) &&
+	  (pedge->w <= threshold[b])) {
+	u->join(a, b);
+	a = u->find(a);
+	threshold[a] = pedge->w + THRESHOLD(u->size(a), c);
+      }
+    }
+  }
+
+  // free up
+  delete threshold;
+  return u;
+}
+
+#endif

segment-image.h

@@ -0,0 +1,154 @@
+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+#ifndef SEGMENT_IMAGE
+#define SEGMENT_IMAGE
+
+#include <cstdlib>
+#include "./image.h"
+#include "./misc.h"
+#include "./filter.h"
+#include "./segment-graph.h"
+
+// random color
+rgb random_rgb(){ 
+  rgb c;
+  double r;
+  
+  c.r = (uchar)random();
+  c.g = (uchar)random();
+  c.b = (uchar)random();
+
+  return c;
+}
+
+// dissimilarity measure between pixels
+static inline float diff(image<float> *r, image<float> *g, image<float> *b,
+			 int x1, int y1, int x2, int y2) {
+  return sqrt(square(imRef(r, x1, y1)-imRef(r, x2, y2)) +
+	      square(imRef(g, x1, y1)-imRef(g, x2, y2)) +
+	      square(imRef(b, x1, y1)-imRef(b, x2, y2)));
+}
+
+/*
+ * Segment an image
+ *
+ * Returns a color image representing the segmentation.
+ *
+ * im: image to segment.
+ * sigma: to smooth the image.
+ * c: constant for treshold function.
+ * min_size: minimum component size (enforced by post-processing stage).
+ * num_ccs: number of connected components in the segmentation.
+ */
+image<rgb> *segment_image(image<rgb> *im, float sigma, float c, int min_size,
+			  int *num_ccs) {
+  int width = im->width();
+  int height = im->height();
+
+  image<float> *r = new image<float>(width, height);
+  image<float> *g = new image<float>(width, height);
+  image<float> *b = new image<float>(width, height);
+
+  // smooth each color channel  
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      imRef(r, x, y) = imRef(im, x, y).r;
+      imRef(g, x, y) = imRef(im, x, y).g;
+      imRef(b, x, y) = imRef(im, x, y).b;
+    }
+  }
+  image<float> *smooth_r = smooth(r, sigma);
+  image<float> *smooth_g = smooth(g, sigma);
+  image<float> *smooth_b = smooth(b, sigma);
+  delete r;
+  delete g;
+  delete b;
+ 
+  // build graph
+  edge *edges = new edge[width*height*4];
+  int num = 0;
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      if (x < width-1) {
+	edges[num].a = y * width + x;
+	edges[num].b = y * width + (x+1);
+	edges[num].w = diff(smooth_r, smooth_g, smooth_b, x, y, x+1, y);
+	num++;
+      }
+
+      if (y < height-1) {
+	edges[num].a = y * width + x;
+	edges[num].b = (y+1) * width + x;
+	edges[num].w = diff(smooth_r, smooth_g, smooth_b, x, y, x, y+1);
+	num++;
+      }
+
+      if ((x < width-1) && (y < height-1)) {
+	edges[num].a = y * width + x;
+	edges[num].b = (y+1) * width + (x+1);
+	edges[num].w = diff(smooth_r, smooth_g, smooth_b, x, y, x+1, y+1);
+	num++;
+      }
+
+      if ((x < width-1) && (y > 0)) {
+	edges[num].a = y * width + x;
+	edges[num].b = (y-1) * width + (x+1);
+	edges[num].w = diff(smooth_r, smooth_g, smooth_b, x, y, x+1, y-1);
+	num++;
+      }
+    }
+  }
+  delete smooth_r;
+  delete smooth_g;
+  delete smooth_b;
+
+  // segment
+  universe *u = segment_graph(width*height, num, edges, c);
+  
+  // post process small components
+  for (int i = 0; i < num; i++) {
+    int a = u->find(edges[i].a);
+    int b = u->find(edges[i].b);
+    if ((a != b) && ((u->size(a) < min_size) || (u->size(b) < min_size)))
+      u->join(a, b);
+  }
+  delete [] edges;
+  *num_ccs = u->num_sets();
+
+  image<rgb> *output = new image<rgb>(width, height);
+
+  // pick random colors for each component
+  rgb *colors = new rgb[width*height];
+  for (int i = 0; i < width*height; i++)
+    colors[i] = random_rgb();
+  
+  for (int y = 0; y < height; y++) {
+    for (int x = 0; x < width; x++) {
+      int comp = u->find(y * width + x);
+      imRef(output, x, y) = colors[comp];
+    }
+  }  
+
+  delete [] colors;  
+  delete u;
+
+  return output;
+}
+
+#endif

segment.cpp

@@ -0,0 +1,49 @@
+/*
+Copyright (C) 2006 Pedro Felzenszwalb
+
+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.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+*/
+
+#include <cstdio>
+#include <cstdlib>
+#include <image.h>
+#include <misc.h>
+#include <pnmfile.h>
+#include "segment-image.h"
+
+int main(int argc, char **argv) {
+  if (argc != 6) {
+    fprintf(stderr, "usage: %s sigma k min input(ppm) output(ppm)\n", argv[0]);
+    return 1;
+  }
+  
+  float sigma = atof(argv[1]);
+  float k = atof(argv[2]);
+  int min_size = atoi(argv[3]);
+	
+  printf("loading input image.\n");
+  image<rgb> *input = loadPPM(argv[4]);
+	
+  printf("processing\n");
+  int num_ccs; 
+  image<rgb> *seg = segment_image(input, sigma, k, min_size, &num_ccs); 
+  savePPM(seg, argv[5]);
+
+  printf("got %d components\n", num_ccs);
+  printf("done! uff...thats hard work.\n");
+
+  return 0;
+}
+