ImagePHash.java

package com.lamoop.competition;

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.color.ColorSpace;
import java.awt.image.BufferedImage;
import java.awt.image.ColorConvertOp;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ImagePHash {

	protected Logger logger = LoggerFactory.getLogger(ImagePHash.class);

	private int size = 32;
	private int smallerSize = 8;

	public ImagePHash() {
		initCoefficients();
	}

	public ImagePHash(int size, int smallerSize) {
		this.size = size;
		this.smallerSize = smallerSize;

		initCoefficients();
	}

	public int distance(String s1, String s2) {
		int counter = 0;
		for (int k = 0; k < s1.length(); k++) {
			if (s1.charAt(k) != s2.charAt(k)) {
				counter++;
			}
		}
		return counter;
	}

	public String getHash(String str) {

		BufferedImage img = new BufferedImage(1500, 100, 1);
		Graphics2D g2d = img.createGraphics();
		g2d.drawImage(img, 0, 0, img.getWidth(), img.getHeight(), null, null);
		AlphaComposite ac = AlphaComposite.getInstance(AlphaComposite.SRC_OVER,
				0.9F);
		g2d.setComposite(ac);
		g2d.setFont(new Font("Arial", Font.BOLD, 80));
		g2d.setColor(Color.WHITE);
		g2d.drawString(str, 10, 80);
		g2d.dispose();
		img = resize(img, size, size);

		img = grayscale(img);

		double[][] vals = new double[size][size];

		for (int x = 0; x < img.getWidth(); x++) {
			for (int y = 0; y < img.getHeight(); y++) {
				vals[x][y] = getBlue(img, x, y);
			}
		}

		double[][] dctVals = applyDCT(vals);

		double total = 0;

		for (int x = 0; x < smallerSize; x++) {
			for (int y = 0; y < smallerSize; y++) {
				total += dctVals[x][y];
			}
		}
		total -= dctVals[0][0];

		double avg = total / (double) ((smallerSize * smallerSize) - 1);

		String hash = "";

		for (int x = 0; x < smallerSize; x++) {
			for (int y = 0; y < smallerSize; y++) {
				if (x != 0 && y != 0) {
					hash += (dctVals[x][y] > avg ? "1" : "0");
				}
			}
		}

		return hash;
	}

	private BufferedImage resize(BufferedImage image, int width, int height) {
		BufferedImage resizedImage = new BufferedImage(width, height,
				BufferedImage.TYPE_INT_ARGB);
		Graphics2D g = resizedImage.createGraphics();
		g.drawImage(image, 0, 0, width, height, null);
		g.dispose();
		return resizedImage;
	}

	private ColorConvertOp colorConvert = new ColorConvertOp(
			ColorSpace.getInstance(ColorSpace.CS_GRAY), null);

	private BufferedImage grayscale(BufferedImage img) {
		colorConvert.filter(img, img);
		return img;
	}

	private static int getBlue(BufferedImage img, int x, int y) {
		return (img.getRGB(x, y)) & 0xff;
	}


	private double[] c;

	private void initCoefficients() {
		c = new double[size];

		for (int i = 1; i < size; i++) {
			c[i] = 1;
		}
		c[0] = 1 / Math.sqrt(2.0);
	}

	private double[][] applyDCT(double[][] f) {
		int N = size;

		double[][] F = new double[N][N];
		for (int u = 0; u < N; u++) {
			for (int v = 0; v < N; v++) {
				double sum = 0.0;
				for (int i = 0; i < N; i++) {
					for (int j = 0; j < N; j++) {
						sum += Math
								.cos(((2 * i + 1) / (2.0 * N)) * u * Math.PI)
								* Math.cos(((2 * j + 1) / (2.0 * N)) * v
										* Math.PI) * (f[i][j]);
					}
				}
				sum *= ((c[u] * c[v]) / 4.0);
				F[u][v] = sum;
			}
		}
		return F;
	}

	public int hmDistance(String str1, String str2) {
		ImagePHash p = new ImagePHash();
		String hash1 = p.getHash(str1);
		String hash2 = p.getHash(str2);
		return p.distance(hash1, hash2);
	}
}