图像分析之直方图分析

  - created by gloomyfish

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 );elseimage.setRGB( x, y, width, height, pixels, 0, width );    }}

测试代码如下：

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);      }  }