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Methods for the extraction of low-level image features, including global image features and pixel/patch classification models.
/**
* Copyright (c) 2011, The University of Southampton and the individual contributors.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* * Neither the name of the University of Southampton nor the names of its
* contributors may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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package org.openimaj.image.segmentation;
import gnu.trove.map.hash.TObjectFloatHashMap;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import org.openimaj.citation.annotation.Reference;
import org.openimaj.citation.annotation.ReferenceType;
import org.openimaj.image.FImage;
import org.openimaj.image.Image;
import org.openimaj.image.MBFImage;
import org.openimaj.image.pixel.ConnectedComponent;
import org.openimaj.image.pixel.Pixel;
import org.openimaj.image.processing.convolution.FGaussianConvolve;
import org.openimaj.image.processor.SinglebandImageProcessor;
import org.openimaj.math.graph.SimpleWeightedEdge;
import org.openimaj.util.set.DisjointSetForest;
/**
* 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.
*
* @author Jonathon Hare ([email protected])
* @param Type of {@link Image}
*/
@Reference(
type = ReferenceType.Article,
author = {"Felzenszwalb, Pedro F.", "Huttenlocher, Daniel P."},
title = "Efficient Graph-Based Image Segmentation",
journal = "Int. J. Comput. Vision",
volume = "59",
number = "2",
month = "September",
year = "2004",
pages = {"167","181"},
url = "http://dx.doi.org/10.1023/B:VISI.0000022288.19776.77",
publisher = "Kluwer Academic Publishers"
)
public class FelzenszwalbHuttenlocherSegmenter & SinglebandImageProcessor.Processable> implements Segmenter {
protected float sigma = 0.5f;
protected float k = 500f / 255f;
protected int minSize = 50;
/**
* Default constructor
*/
public FelzenszwalbHuttenlocherSegmenter() {}
/**
* Construct with the given parameters
* @param sigma amount of blurring
* @param k threshold
* @param minSize minimum allowed component size
*/
public FelzenszwalbHuttenlocherSegmenter(float sigma, float k, int minSize) {
this.sigma = sigma;
this.k = k;
this.minSize = minSize;
}
@Override
public List segment(I image) {
if (((Object)image) instanceof MBFImage) {
return segmentImage((MBFImage)((Object)image));
} else {
return segmentImage(new MBFImage((FImage)((Object)image)));
}
}
private float diff(MBFImage image, Pixel p1, Pixel p2) {
float sum = 0;
for (FImage band : image.bands) {
float d = band.pixels[p1.y][p1.x] - band.pixels[p2.y][p2.x];
sum += d*d;
}
return (float) Math.sqrt(sum);
}
protected List segmentImage(MBFImage im) {
int width = im.getWidth();
int height = im.getHeight();
MBFImage smooth = im.process(new FGaussianConvolve(sigma));
// build graph
List> edges = new ArrayList>();
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
if (x < width-1) {
SimpleWeightedEdge p = new SimpleWeightedEdge();
p.from = new Pixel(x, y);
p.to = new Pixel(x+1, y);
p.weight = diff(smooth, p.from, p.to);
edges.add(p);
}
if (y < height-1) {
SimpleWeightedEdge p = new SimpleWeightedEdge();
p.from = new Pixel(x, y);
p.to = new Pixel(x, y+1);
p.weight = diff(smooth, p.from, p.to);
edges.add(p);
}
if ((x < width-1) && (y < height-1)) {
SimpleWeightedEdge p = new SimpleWeightedEdge();
p.from = new Pixel(x, y);
p.to = new Pixel(x+1, y+1);
p.weight = diff(smooth, p.from, p.to);
edges.add(p);
}
if ((x < width-1) && (y > 0)) {
SimpleWeightedEdge p = new SimpleWeightedEdge();
p.from = new Pixel(x, y);
p.to = new Pixel(x+1, y-1);
p.weight = diff(smooth, p.from, p.to);
edges.add(p);
}
}
}
// segment
DisjointSetForest u = segmentGraph(width*height, edges);
// post process small components
for (int i = 0; i < edges.size(); i++) {
Pixel a = u.find(edges.get(i).from);
Pixel b = u.find(edges.get(i).to);
if ((a != b) && ((u.size(a) < minSize) || (u.size(b) < minSize)))
u.union(a, b);
}
Set> subsets = u.getSubsets();
List ccs = new ArrayList();
for (Set sp : subsets) ccs.add(new ConnectedComponent(sp));
return ccs;
}
protected DisjointSetForest segmentGraph(int numVertices, List> edges) {
// sort edges by weight
Collections.sort(edges, SimpleWeightedEdge.ASCENDING_COMPARATOR);
// make a disjoint-set forest
DisjointSetForest u = new DisjointSetForest(numVertices);
for (SimpleWeightedEdge edge : edges) {
u.add(edge.from);
u.add(edge.to);
}
// init thresholds
TObjectFloatHashMap threshold = new TObjectFloatHashMap();
for (Pixel p : u) {
threshold.put(p, k);
}
// for each edge, in non-decreasing weight order...
for (int i = 0; i < edges.size(); i++) {
SimpleWeightedEdge pedge = edges.get(i);
// components connected by this edge
Pixel a = u.find(pedge.from);
Pixel b = u.find(pedge.to);
if (a != b) {
if ((pedge.weight <= threshold.get(a)) && (pedge.weight <= threshold.get(b))) {
a = u.union(a, b);
threshold.put(a, pedge.weight + (k / u.size(a)));
}
}
}
return u;
}
}
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