LIRe 源代码分析 6：检索（ImageSearcher）[以颜色布局为例]
注：此前写了一系列的文章，分析LIRe的源代码，在此列一个列表：
LIRe 源代码分析 1：整体结构LIRe 源代码分析 2：基本接口（DocumentBuilder）
LIRe 源代码分析 3：基本接口（ImageSearcher）
LIRe 源代码分析 4：建立索引（DocumentBuilder）[以颜色布局为例]
LIRe 源代码分析 5：提取特征向量[以颜色布局为例]
LIRe 源代码分析 6：检索（ImageSearcher）[以颜色布局为例]
LIRe 源代码分析 7：算法类[以颜色布局为例]
前几篇文章介绍了LIRe 的基本接口：
LIRe 源代码分析 1：整体结构LIRe 源代码分析 2：基本接口（DocumentBuilder）
LIRe 源代码分析 3：基本接口（ImageSearcher）
以及其建立索引（DocumentBuilder）[以颜色直方图为例]
LIRe 源代码分析 4：建立索引（DocumentBuilder）[以颜色布局为例]
LIRe 源代码分析 5：提取特征向量[以颜色布局为例]
现在来看一看它的检索部分（ImageSearcher）。不同的方法的检索功能的类各不相同，它们都位于“net.semanticmetadata.lire.impl”中，如下图所示：
在这里仅分析一个比较有代表性的：颜色布局。前文已经分析过ColorLayoutDocumentBuilder，在这里我们分析一下ColorLayoutImageSearcher。源代码如下：
/*
* This file is part of the LIRe project: http://www.semanticmetadata.net/lire
* LIRe 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.
*
* LIRe 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 LIRe; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* We kindly ask you to refer the following paper in any publication mentioning Lire:
*
* Lux Mathias, Savvas A. Chatzichristofis. Lire: Lucene Image Retrieval 鈥�
* An Extensible Java CBIR Library. In proceedings of the 16th ACM International
* Conference on Multimedia, pp. 1085-1088, Vancouver, Canada, 2008
*
* http://doi.acm.org/10.1145/1459359.1459577
*
* Copyright statement:
* --------------------
* (c) 2002-2011 by Mathias Lux (mathias@juggle.at)
* http://www.semanticmetadata.net/lire
*/
package net.semanticmetadata.lire.impl;
import net.semanticmetadata.lire.DocumentBuilder;
import net.semanticmetadata.lire.ImageDuplicates;
import net.semanticmetadata.lire.ImageSearchHits;
import net.semanticmetadata.lire.imageanalysis.ColorLayout;
import net.semanticmetadata.lire.imageanalysis.LireFeature;
import org.apache.lucene.document.Document;
import org.apache.lucene.index.IndexReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.logging.Level;
/**
* Provides a faster way of searching based on byte arrays instead of Strings. The method
* {@link net.semanticmetadata.lire.imageanalysis.ColorLayout#getByteArrayRepresentation()} is used
* to generate the signature of the descriptor much faster. First tests have shown that this
* implementation is up to 4 times faster than the implementation based on strings
* (for 120,000 images)
* <p/>
* User: Mathias Lux, mathias@juggle.at
* Date: 30.06 2011
*/
public class ColorLayoutImageSearcher extends GenericImageSearcher {
public ColorLayoutImageSearcher(int maxHits) {
super(maxHits, ColorLayout.class, DocumentBuilder.FIELD_NAME_COLORLAYOUT_FAST);
}
protected float getDistance(Document d, LireFeature lireFeature) {
float distance = 0f;
ColorLayout lf;
try {
lf = (ColorLayout) descriptorClass.newInstance();
byte[] cls = d.getBinaryValue(fieldName);
if (cls != null && cls.length > 0) {
lf.setByteArrayRepresentation(cls);
distance = lireFeature.getDistance(lf);
} else {
logger.warning("No feature stored in this document ...");
}
} catch (InstantiationException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
} catch (IllegalAccessException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
}
return distance;
}
public ImageSearchHits search(Document doc, IndexReader reader) throws IOException {
SimpleImageSearchHits searchHits = null;
try {
ColorLayout lireFeature = (ColorLayout) descriptorClass.newInstance();
byte[] cls = doc.getBinaryValue(fieldName);
if (cls != null && cls.length > 0)
lireFeature.setByteArrayRepresentation(cls);
float maxDistance = findSimilar(reader, lireFeature);
searchHits = new SimpleImageSearchHits(this.docs, maxDistance);
} catch (InstantiationException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
} catch (IllegalAccessException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
}
return searchHits;
}
public ImageDuplicates findDuplicates(IndexReader reader) throws IOException {
// get the first document:
SimpleImageDuplicates simpleImageDuplicates = null;
try {
if (!IndexReader.indexExists(reader.directory()))
throw new FileNotFoundException("No index found at this specific location.");
Document doc = reader.document(0);
ColorLayout lireFeature = (ColorLayout) descriptorClass.newInstance();
byte[] cls = doc.getBinaryValue(fieldName);
if (cls != null && cls.length > 0)
lireFeature.setByteArrayRepresentation(cls);
HashMap<Float, List<String>> duplicates = new HashMap<Float, List<String>>();
// find duplicates ...
boolean hasDeletions = reader.hasDeletions();
int docs = reader.numDocs();
int numDuplicates = 0;
for (int i = 0; i < docs; i++) {
if (hasDeletions && reader.isDeleted(i)) {
continue;
}
Document d = reader.document(i);
float distance = getDistance(d, lireFeature);
if (!duplicates.containsKey(distance)) {
duplicates.put(distance, new LinkedList<String>());
} else {
numDuplicates++;
}
duplicates.get(distance).add(d.getFieldable(DocumentBuilder.FIELD_NAME_IDENTIFIER).stringValue());
}
if (numDuplicates == 0) return null;
LinkedList<List<String>> results = new LinkedList<List<String>>();
for (float f : duplicates.keySet()) {
if (duplicates.get(f).size() > 1) {
results.add(duplicates.get(f));
}
}
simpleImageDuplicates = new SimpleImageDuplicates(results);
} catch (InstantiationException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
} catch (IllegalAccessException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
}
return simpleImageDuplicates;
}
}
源代码里面重要的函数有3个：
float getDistance(Document d, LireFeature lireFeature)：
ImageSearchHits search(Document doc, IndexReader reader)：检索。最核心函数。
ImageDuplicates findDuplicates(IndexReader reader)：目前还没研究。
在这里忽然发现了一个问题：这里竟然只有一个Search()？！应该是有参数不同的3个Search()才对啊......
经过研究后发现，ColorLayoutImageSearcher继承了一个类——GenericImageSearcher，而不是继承AbstractImageSearcher。Search()方法的实现是在GenericImageSearcher中实现的。看来这个ColorLayoutImageSearcher还挺特殊的啊......
看一下GenericImageSearcher的源代码：
package net.semanticmetadata.lire.impl;
import net.semanticmetadata.lire.AbstractImageSearcher;
import net.semanticmetadata.lire.DocumentBuilder;
import net.semanticmetadata.lire.ImageDuplicates;
import net.semanticmetadata.lire.ImageSearchHits;
import net.semanticmetadata.lire.imageanalysis.LireFeature;
import net.semanticmetadata.lire.utils.ImageUtils;
import org.apache.lucene.document.Document;
import org.apache.lucene.index.IndexReader;
import java.awt.image.BufferedImage;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.TreeSet;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* This file is part of the Caliph and Emir project: http://www.SemanticMetadata.net
* <br>Date: 01.02.2006
* <br>Time: 00:17:02
*
* @author Mathias Lux, mathias@juggle.at
*/
public class GenericImageSearcher extends AbstractImageSearcher {
protected Logger logger = Logger.getLogger(getClass().getName());
Class<?> descriptorClass;
String fieldName;
private int maxHits = 10;
protected TreeSet<SimpleResult> docs;
public GenericImageSearcher(int maxHits, Class<?> descriptorClass, String fieldName) {
this.maxHits = maxHits;
docs = new TreeSet<SimpleResult>();
this.descriptorClass = descriptorClass;
this.fieldName = fieldName;
}
public ImageSearchHits search(BufferedImage image, IndexReader reader) throws IOException {
logger.finer("Starting extraction.");
LireFeature lireFeature = null;
SimpleImageSearchHits searchHits = null;
try {
lireFeature = (LireFeature) descriptorClass.newInstance();
// Scaling image is especially with the correlogram features very important!
BufferedImage bimg = image;
if (Math.max(image.getHeight(), image.getWidth()) > GenericDocumentBuilder.MAX_IMAGE_DIMENSION) {
bimg = ImageUtils.scaleImage(image, GenericDocumentBuilder.MAX_IMAGE_DIMENSION);
}
lireFeature.extract(bimg);
logger.fine("Extraction from image finished");
float maxDistance = findSimilar(reader, lireFeature);
searchHits = new SimpleImageSearchHits(this.docs, maxDistance);
} catch (InstantiationException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
} catch (IllegalAccessException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
}
return searchHits;
}
/**
* @param reader
* @param lireFeature
* @return the maximum distance found for normalizing.
* @throws java.io.IOException
*/
protected float findSimilar(IndexReader reader, LireFeature lireFeature) throws IOException {
float maxDistance = -1f, overallMaxDistance = -1f;
boolean hasDeletions = reader.hasDeletions();
// clear result set ...
docs.clear();
int docs = reader.numDocs();
for (int i = 0; i < docs; i++) {
// bugfix by Roman Kern
if (hasDeletions && reader.isDeleted(i)) {
continue;
}
Document d = reader.document(i);
float distance = getDistance(d, lireFeature);
assert (distance >= 0);
// calculate the overall max distance to normalize score afterwards
if (overallMaxDistance < distance) {
overallMaxDistance = distance;
}
// if it is the first document:
if (maxDistance < 0) {
maxDistance = distance;
}
// if the array is not full yet:
if (this.docs.size() < maxHits) {
this.docs.add(new SimpleResult(distance, d));
if (distance > maxDistance) maxDistance = distance;
} else if (distance < maxDistance) {
// if it is nearer to the sample than at least on of the current set:
// remove the last one ...
this.docs.remove(this.docs.last());
// add the new one ...
this.docs.add(new SimpleResult(distance, d));
// and set our new distance border ...
maxDistance = this.docs.last().getDistance();
}
}
return maxDistance;
}
protected float getDistance(Document d, LireFeature lireFeature) {
float distance = 0f;
LireFeature lf;
try {
lf = (LireFeature) descriptorClass.newInstance();
String[] cls = d.getValues(fieldName);
if (cls != null && cls.length > 0) {
lf.setStringRepresentation(cls[0]);
distance = lireFeature.getDistance(lf);
} else {
logger.warning("No feature stored in this document!");
}
} catch (InstantiationException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
} catch (IllegalAccessException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
}
return distance;
}
public ImageSearchHits search(Document doc, IndexReader reader) throws IOException {
SimpleImageSearchHits searchHits = null;
try {
LireFeature lireFeature = (LireFeature) descriptorClass.newInstance();
String[] cls = doc.getValues(fieldName);
if (cls != null && cls.length > 0)
lireFeature.setStringRepresentation(cls[0]);
float maxDistance = findSimilar(reader, lireFeature);
searchHits = new SimpleImageSearchHits(this.docs, maxDistance);
} catch (InstantiationException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
} catch (IllegalAccessException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
}
return searchHits;
}
public ImageDuplicates findDuplicates(IndexReader reader) throws IOException {
// get the first document:
SimpleImageDuplicates simpleImageDuplicates = null;
try {
if (!IndexReader.indexExists(reader.directory()))
throw new FileNotFoundException("No index found at this specific location.");
Document doc = reader.document(0);
LireFeature lireFeature = (LireFeature) descriptorClass.newInstance();
String[] cls = doc.getValues(fieldName);
if (cls != null && cls.length > 0)
lireFeature.setStringRepresentation(cls[0]);
HashMap<Float, List<String>> duplicates = new HashMap<Float, List<String>>();
// find duplicates ...
boolean hasDeletions = reader.hasDeletions();
int docs = reader.numDocs();
int numDuplicates = 0;
for (int i = 0; i < docs; i++) {
if (hasDeletions && reader.isDeleted(i)) {
continue;
}
Document d = reader.document(i);
float distance = getDistance(d, lireFeature);
if (!duplicates.containsKey(distance)) {
duplicates.put(distance, new LinkedList<String>());
} else {
numDuplicates++;
}
duplicates.get(distance).add(d.getFieldable(DocumentBuilder.FIELD_NAME_IDENTIFIER).stringValue());
}
if (numDuplicates == 0) return null;
LinkedList<List<String>> results = new LinkedList<List<String>>();
for (float f : duplicates.keySet()) {
if (duplicates.get(f).size() > 1) {
results.add(duplicates.get(f));
}
}
simpleImageDuplicates = new SimpleImageDuplicates(results);
} catch (InstantiationException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
} catch (IllegalAccessException e) {
logger.log(Level.SEVERE, "Error instantiating class for generic image searcher: " + e.getMessage());
}
return simpleImageDuplicates;
}
public String toString() {
return "GenericSearcher using " + descriptorClass.getName();
}
}
下面来看看GenericImageSearcher中的search(BufferedImage image, IndexReader reader)函数的步骤（注：这个函数应该是用的最多的，输入一张图片，返回相似图片的结果集）：
1.输入图片如果尺寸过大（大于1024），则调整尺寸。
2.使用extract()提取输入图片的特征值。
3.根据提取的特征值，使用findSimilar()查找相似的图片。
4.新建一个ImageSearchHits用于存储查找的结果。
5.返回ImageSearchHits
在这里要注意一点：
GenericImageSearcher中创建特定方法的类的时候，使用了如下形式：
LireFeature lireFeature = (LireFeature) descriptorClass.newInstance();
即接口的方式，而不是直接新建一个对象的方式，形如：
AutoColorCorrelogram acc = new AutoColorCorrelogram(CorrelogramDocumentBuilder.MAXIMUM_DISTANCE)
相比而言，更具有通用型。
在search()函数中，调用了一个函数findSimilar()。这个函数的作用是查找相似图片的，分析了一下它的步骤：
1.使用IndexReader获取所有的记录
2.遍历所有的记录，和当前输入的图片进行比较，使用getDistance()函数
3.获取maxDistance并返回
在findSimilar()中，又调用了一个getDistance()，该函数调用了具体检索方法的getDistance()函数。
下面我们来看一下ColorLayout类中的getDistance()函数：
public float getDistance(LireFeature descriptor) {
if (!(descriptor instanceof ColorLayoutImpl)) return -1f;
ColorLayoutImpl cl = (ColorLayoutImpl) descriptor;
return (float) ColorLayoutImpl.getSimilarity(YCoeff, CbCoeff, CrCoeff, cl.YCoeff, cl.CbCoeff, cl.CrCoeff);
}发现其调用了ColorLayoutImpl类中的getSimilarity()函数：
public static double getSimilarity(int[] YCoeff1, int[] CbCoeff1, int[] CrCoeff1, int[] YCoeff2, int[] CbCoeff2, int[] CrCoeff2) {
int numYCoeff1, numYCoeff2, CCoeff1, CCoeff2, YCoeff, CCoeff;
//Numbers of the Coefficients of two descriptor values.
numYCoeff1 = YCoeff1.length;
numYCoeff2 = YCoeff2.length;
CCoeff1 = CbCoeff1.length;
CCoeff2 = CbCoeff2.length;
//take the minimal Coeff-number
YCoeff = Math.min(numYCoeff1, numYCoeff2);
CCoeff = Math.min(CCoeff1, CCoeff2);
setWeightingValues();
int j;
int[] sum = new int[3];
int diff;
sum[0] = 0;
for (j = 0; j < YCoeff; j++) {
diff = (YCoeff1[j] - YCoeff2[j]);
sum[0] += (weightMatrix[0][j] * diff * diff);
}
sum[1] = 0;
for (j = 0; j < CCoeff; j++) {
diff = (CbCoeff1[j] - CbCoeff2[j]);
sum[1] += (weightMatrix[1][j] * diff * diff);
}
sum[2] = 0;
for (j = 0; j < CCoeff; j++) {
diff = (CrCoeff1[j] - CrCoeff2[j]);
sum[2] += (weightMatrix[2][j] * diff * diff);
}
//returns the distance between the two desciptor values
return Math.sqrt(sum[0] * 1.0) + Math.sqrt(sum[1] * 1.0) + Math.sqrt(sum[2] * 1.0);
}由代码可见，getSimilarity()通过具体的算法，计算两张图片特征向量之间的相似度。
