Otsu Thresholding

今天复习Otsu算法，它利用阈值奖图片转成黑白色。Otsu算法是二值算法，目的是求出一个Threshhold，来最小化Within-Class方差，这等价最大化between-class方差。下面用java来实现算法。

package com.lili.ots<pre name="code" class="java">package com.lili.otsu;
public class OtsuThresholder
{private int histData[];private int maxLevelValue;private int threshold;public OtsuThresholder(){histData = new int[256];}public int[] getHistData(){return histData;}public int getMaxLevelValue(){return maxLevelValue;}public int getThreshold(){return threshold;}public int doThreshold(byte[] srcData, byte[] monoData){int ptr;// Clear histogram data// Set all values to zeroptr = 0;while (ptr < histData.length) histData[ptr++] = 0;// Calculate histogram and find the level with the max value// Note: the max level value isn't required by the Otsu methodptr = 0;maxLevelValue = 0;while (ptr < srcData.length){int h = 0xFF & srcData[ptr];  histData[h] ++;if (histData[h] > maxLevelValue) maxLevelValue = histData[h];ptr ++;}// Total number of pixelsint total = srcData.length;                //48*57 image, total=48*57float sum = 0;for (int t=0 ; t<256 ; t++) sum += t * histData[t];float sumB = 0;int wB = 0;int wF = 0;float varMax = 0;threshold = 0;for (int t=0 ; t<256 ; t++){wB += histData[t];                 // Weight Background if (wB == 0) continue;   // 'cause divide           the number of pixle of backgroundwF = total - wB;                      // Weight Foregroundif (wF == 0) break;                sumB += (float) (t * histData[t]);float mB = sumB / wB;             // Mean Backgroundfloat mF = (sum - sumB) / wF;        // Mean Foreground// Calculate Between Class Variancefloat varBetween = (float)wB * (float)wF * (mB - mF) * (mB - mF); // Check if new maximum foundif (varBetween > varMax) {varMax = varBetween;threshold = t;}}// Apply threshold to create binary imageif (monoData != null){ptr = 0;while (ptr < srcData.length)            // 48*57{monoData[ptr] = ((0xFF & srcData[ptr]) >= threshold) ? (byte) 255 : 0;ptr ++;}}return threshold;}
}

package com.lili.otsu;import java.io.*;import java.util.*;
import java.awt.*;
import java.awt.image.*;
import javax.swing.*;import com.lili.otsu.GreyFrame;
import com.lili.otsu.OtsuThresholder;public class OtsuDemo
{public OtsuDemo(String filename){// Load Source imageBufferedImage srcImage = null;try{File imgFile = new File(filename);srcImage = javax.imageio.ImageIO.read(imgFile);}catch (IOException ioE){System.err.println(ioE);System.exit(1);}int width = srcImage.getWidth();int height = srcImage.getHeight();// Get raw image dataRaster raster = srcImage.getData();DataBuffer buffer = raster.getDataBuffer();int type = buffer.getDataType();if (type != DataBuffer.TYPE_BYTE){System.err.println("Wrong image data type");System.exit(1);}if (buffer.getNumBanks() != 1){System.err.println("Wrong image data format");System.exit(1);}DataBufferByte byteBuffer = (DataBufferByte) buffer;byte[] srcData = byteBuffer.getData(0);// Sanity check imageif (width * height  != srcData.length) {System.err.println("Unexpected image data size. Should be greyscale image");System.exit(1);}// Output Image infoSystem.out.printf("Loaded image: '%s', width: %d, height: %d, num bytes: %d\n", filename, width, height, srcData.length);byte[] dstData = new byte[srcData.length];// Create Otsu ThresholderOtsuThresholder thresholder = new OtsuThresholder();int threshold = thresholder.doThreshold(srcData, dstData);System.out.printf("Threshold: %d\n", threshold);// Create GUIGreyFrame srcFrame = new GreyFrame(width, height, srcData);GreyFrame dstFrame = new GreyFrame(width, height, dstData);GreyFrame histFrame = createHistogramFrame(thresholder);JPanel infoPanel = new JPanel();infoPanel.add(histFrame);JPanel panel = new JPanel(new BorderLayout(5, 5));panel.setBorder(new javax.swing.border.EmptyBorder(5, 5, 5, 5));panel.add(infoPanel, BorderLayout.NORTH);panel.add(srcFrame, BorderLayout.WEST);panel.add(dstFrame, BorderLayout.EAST);panel.add(new JLabel("QingrouShui", JLabel.CENTER), BorderLayout.SOUTH);JFrame frame = new JFrame("QingrouShui");frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.getContentPane().add(panel);frame.pack();frame.setVisible(true);// Save Imagestry{int dotPos = filename.lastIndexOf(".");String basename = filename.substring(0,dotPos);javax.imageio.ImageIO.write(dstFrame.getBufferImage(), "PNG", new File(basename+"_BW.png"));javax.imageio.ImageIO.write(histFrame.getBufferImage(), "PNG", new File(basename+"_hist.png"));}catch (IOException ioE){System.err.println("Could not write image " + filename);}}private GreyFrame createHistogramFrame(OtsuThresholder thresholder){int numPixels = 256 * 100;byte[] histPlotData = new byte[numPixels];int[] histData = thresholder.getHistData();int max = thresholder.getMaxLevelValue();int threshold = thresholder.getThreshold();for (int l=0 ; l<256 ; l++){int ptr = (numPixels - 256) + l;int val = (100 * histData[l]) / max;if (l == threshold){for (int i=0 ; i<100 ; i++, ptr-=256) histPlotData[ptr] = (byte) 128;}else{for (int i=0 ; i<100 ; i++, ptr-=256) histPlotData[ptr] = (val < i) ? (byte) 255 : 0;}}return new GreyFrame(256, 100, histPlotData);}public static void main(String args[]){new OtsuDemo("lili_icmv12.png");System.out.println("QingrouShui");
//      if (args.length<1) {
//          System.err.println("Provide image filename");
//          System.exit(1);
//      }}
}

<pre name="code" class="java">package com.lili.otsu;
import java.awt.*;import javax.swing.*;
import java.awt.image.*;
import java.awt.color.*;public class GreyFrame extends JComponent
{private int width;private int height;private Dimension size;private BufferedImage image;private String title;public GreyFrame(int width, int height, byte[] data){this(width, height, data, null);}public GreyFrame(int width, int height, byte[] data, String title){this.width = width;this.height = height;this.title = title;size = new Dimension(width, height);DataBufferByte dataBuffer = new DataBufferByte(data, data.length, 0);PixelInterleavedSampleModel sampleModel = new PixelInterleavedSampleModel(DataBuffer.TYPE_BYTE, width, height, 1, width, new int[] {0});ColorSpace colourSpace = ColorSpace.getInstance(ColorSpace.CS_GRAY);ComponentColorModel colourModel = new ComponentColorModel(colourSpace, new int[] {8}, false, false, Transparency.OPAQUE, DataBuffer.TYPE_BYTE);WritableRaster raster = Raster.createWritableRaster(sampleModel, dataBuffer, null);image = new BufferedImage(colourModel, raster, false, null);}public Graphics2D getBufferImageGraphics(){return image.createGraphics();}public BufferedImage getBufferImage(){return image;}public Dimension getSize(){return size;}public Dimension getPreferredSize(){return size;}public void paint(Graphics g){super.paint(g);if (image != null) g.drawImage(image, 0, 0, this);if (title != null) {g.setColor(Color.RED);g.drawString(title, 5, height - 5);}}
}

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