ColourExtractor.java

/**
 * 
 */
package uk.bl.wa.tika.parser.imagefeatures;

/**
 * @author Andrew Jackson <Andrew.Jackson@bl.uk>
 *
 */
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import org.apache.sanselan.Sanselan;

/**
 * 
 * Prototype colour extractor.
 * 
 * Examines images files, skipping pixels for big images, and determines the most common colour.
 * 
 * Uses the ColourMatcher to return this as text.
 * 
 * Based on:
 * http://stackoverflow.com/questions/4427200/getting-the-most-common-color-of-a-image
 * 
 * @author Andrew Jackson <Andrew.Jackson@bl.uk>
 *
 */
public class ColourExtractor {


	public static void main(String args[]) throws Exception {
		File file = new File("src/test/resources/16px-photo.jpg");

		BufferedImage image = Sanselan.getBufferedImage(file);

		int height = image.getHeight();
		int hstep = Math.max(1, height/100);
		int width = image.getWidth();
		int wstep = Math.max(1, width/100);

		Map<Integer, Integer> m = new HashMap<Integer, Integer>();
		for(int i=0; i < width ; i+=wstep)
		{
			for(int j=0; j < height ; j+=hstep)
			{
				int rgb = image.getRGB(i, j);
				//int[] rgbArr = getRGBArr(rgb);
				//if( ! isGray(rgbArr) ) {
				Integer counter = (Integer) m.get(rgb);   
				if (counter == null)
					counter = 0;
				counter++;                                
				m.put(rgb, counter);
				//}
			}
		}        
		int[] ccrgb = getMostCommonColour(m);
		System.out.println(intsToHex(ccrgb));
		ColourMatcher cm = new ColourMatcher();
		System.out.println(cm.getMatch(ccrgb[0], ccrgb[1], ccrgb[2]).getName());

	}


	public static int[] getMostCommonColour(Map<Integer,Integer> map) {
		List<Entry<Integer, Integer>> list = new LinkedList<Map.Entry<Integer,Integer>>(map.entrySet());
		Collections.sort(list, new Comparator<Map.Entry<Integer,Integer>>() {
			public int compare(Map.Entry<Integer,Integer> o1, Map.Entry<Integer,Integer> o2) {
				return (o1.getValue()).compareTo(o2.getValue());
			}
		});    
		Map.Entry<Integer,Integer> me = list.get(list.size()-1);
		return getRGBArr((Integer)me.getKey());
	}

	private static String intsToHex( int[] rgb ) {
		return Integer.toHexString(rgb[0])+" "+Integer.toHexString(rgb[1])+" "+Integer.toHexString(rgb[2]);            	
	}

	private static int[] getRGBArr(int pixel) {
		//int alpha = (pixel >> 24) & 0xff;
		int red = (pixel >> 16) & 0xff;
		int green = (pixel >> 8) & 0xff;
		int blue = (pixel) & 0xff;
		return new int[]{red,green,blue};

	}
	
	@SuppressWarnings("unused")
	private static boolean isGray(int[] rgbArr) {
		int rgDiff = rgbArr[0] - rgbArr[1];
		int rbDiff = rgbArr[0] - rgbArr[2];
		// Filter out black, white and grays...... (tolerance within 10 pixels)
		int tolerance = 10;
		if (rgDiff > tolerance || rgDiff < -tolerance) 
			if (rbDiff > tolerance || rbDiff < -tolerance) { 
				return false;
			}                 
		return true;
	}

}