图像分析之直方图分析

图像分析之强度直方图分析

直方图介绍

强度直方图图形化显示不同的像素值在不同的强度值上的出现频率，对于灰度图像来说强度

范围为[0~255]之间，对于RGB的彩色图像可以独立显示三种颜色的强度直方图。强度直方

图是用来寻找灰度图像二值化阈值常用而且是有效的手段之一，如果一幅灰度图像的直方图

显示为两个波峰，则二值化阈值应该是这两个波峰之间的某个灰度值。同时强度直方图是调

整图像对比度的重要依据

直方图实现方法：

对一幅灰度图像从上到下，从左到右扫描每个像素值，在每个灰度值上计算像素数目，以这

些数据为基础完成图像直方图的绘制。

运行效果如下：

程序实现：

1.      首先对一幅RGB图像完成灰度转换，转换代码如下：

2.      初始化直方图数据数组int[256] 因为灰度值的范围为0～255

3.      扫描灰度图像，完成强度数据计算。

4.      使用Java 2D绘制直方图

直方图实现源代码：

package com.gloomyfish.image.analysis;

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;

public class HistogramAnalysisAlg {
	private BufferedImage srcImage;
	private BufferedImage histogramImage;
	private int size = 280;
	
	public HistogramAnalysisAlg(BufferedImage srcImage){
		histogramImage = new BufferedImage(size,size, BufferedImage.TYPE_4BYTE_ABGR);
		this.srcImage = srcImage;
	}
	
	public BufferedImage getHistogram() {
        int[] inPixels = new int[srcImage.getWidth()*srcImage.getHeight()];
        int[] intensity = new int[256];
        for(int i=0; i<intensity.length; i++) {
        	intensity[i] = 0;
        }
        getRGB( srcImage, 0, 0, srcImage.getWidth(), srcImage.getHeight(), inPixels );
        int index = 0;
        for(int row=0; row<srcImage.getHeight(); row++) {
        	int ta = 0, tr = 0, tg = 0, tb = 0;
        	for(int col=0; col<srcImage.getWidth(); col++) {
        		index = row * srcImage.getWidth() + col;
        		ta = (inPixels[index] >> 24) & 0xff;
                tr = (inPixels[index] >> 16) & 0xff;
                tg = (inPixels[index] >> 8) & 0xff;
                tb = inPixels[index] & 0xff;
                int gray = (int)(0.299 * (double)tr + 0.587 * (double)tg + 0.114 * (double)tb);
                intensity[gray]++;
        	}
        }
        
        // draw XY Axis lines
        Graphics2D g2d = histogramImage.createGraphics();
        g2d.setPaint(Color.BLACK);
        g2d.fillRect(0, 0, size, size);
        g2d.setPaint(Color.WHITE);
        g2d.drawLine(5, 250, 265, 250);
        g2d.drawLine(5, 250, 5, 5);
        
        // scale to 200
        g2d.setPaint(Color.GREEN);
        int max = findMaxValue(intensity);
        float rate = 200.0f/((float)max);
        int offset = 2;
        for(int i=0; i<intensity.length; i++) {
        	int frequency = (int)(intensity[i] * rate);
        	g2d.drawLine(5 + offset + i, 250, 5 + offset + i, 250-frequency);
        }
        
        // X Axis Gray intensity
        g2d.setPaint(Color.RED);
        g2d.drawString("Gray Intensity", 100, 270);
		return histogramImage;
	}
	
	private int findMaxValue(int[] intensity) {
		int max = -1;
		for(int i=0; i<intensity.length; i++) {
			if(max < intensity[i]) {
				max = intensity[i];
			}
		}
		return max;
	}

	/**
	 * A convenience method for getting ARGB pixels from an image. This tries to avoid the performance
	 * penalty of BufferedImage.getRGB unmanaging the image.
	 */
	public int[] getRGB( BufferedImage image, int x, int y, int width, int height, int[] pixels ) {
		int type = image.getType();
		if ( type == BufferedImage.TYPE_INT_ARGB || type == BufferedImage.TYPE_INT_RGB )
			return (int [])image.getRaster().getDataElements( x, y, width, height, pixels );
		return image.getRGB( x, y, width, height, pixels, 0, width );
    }

	/**
	 * A convenience method for setting ARGB pixels in an image. This tries to avoid the performance
	 * penalty of BufferedImage.setRGB unmanaging the image.
	 */
	public void setRGB( BufferedImage image, int x, int y, int width, int height, int[] pixels ) {
		int type = image.getType();
		if ( type == BufferedImage.TYPE_INT_ARGB || type == BufferedImage.TYPE_INT_RGB )
			image.getRaster().setDataElements( x, y, width, height, pixels );
		else
			image.setRGB( x, y, width, height, pixels, 0, width );
    }

}

package com.gloomyfish.image.analysis;

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.MediaTracker;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JComponent;
import javax.swing.JFileChooser;
import javax.swing.JFrame;

public class ImageAnalysisUI  extends JComponent {
	/**
	 * 
	 */
	private static final long serialVersionUID = 1518574788794973574L;
	private BufferedImage rawImg;
	private BufferedImage modImg;
	private MediaTracker tracker;
	private Dimension mySize;
	
	
	public ImageAnalysisUI(File f) {
		try {
			rawImg = ImageIO.read(f);
			HistogramAnalysisAlg filter = new HistogramAnalysisAlg(rawImg);
			modImg = filter.getHistogram();
		} catch (IOException e1) {
			e1.printStackTrace();
		}
		
		tracker = new MediaTracker(this);
		tracker.addImage(rawImg, 1);
		
		// blocked 10 seconds to load the image data
		try {
			if (!tracker.waitForID(1, 10000)) {
				System.out.println("Load error.");
				System.exit(1);
			}// end if
		} catch (InterruptedException e) {
			e.printStackTrace();
			System.exit(1);
		}// end catch
		
		mySize = new Dimension(2*rawImg.getWidth() + 20, rawImg.getHeight()*2);
		JFrame imageFrame = new JFrame("Gloomyfish - Image Analysis");
		imageFrame.getContentPane().add(this);
		imageFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		imageFrame.pack();
		imageFrame.setVisible(true);
	}
	
	public void paint(Graphics g) {
		Graphics2D g2 = (Graphics2D) g;
		g2.drawImage(rawImg, 0, 0, rawImg.getWidth(), rawImg.getHeight(), null);
		g2.drawImage(modImg, rawImg.getWidth()+10, 0, modImg.getWidth(), modImg.getHeight(), null);
		g2.drawString("source image", 10, rawImg.getHeight() +10);
		g2.drawString("connected component labeled area", 10 + modImg.getWidth(), rawImg.getHeight() +10);
	}
	public Dimension getPreferredSize() {
		return mySize;
	}
	
	public Dimension getMinimumSize() {
		return mySize;
	}
	
	public Dimension getMaximumSize() {
		return mySize;
	}
	
	public static void main(String[] args) {
		JFileChooser chooser = new JFileChooser();
		chooser.showOpenDialog(null);
		File f = chooser.getSelectedFile();
		new ImageAnalysisUI(f);
	}
}