主要代碼如下：
package chapter6;

import java.awt.*;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;

/**

• Created by LENOVO on 18-2-1.
  */
  public class Histogram extends AbstractBufferedImageOp {

  public BufferedImage filter(BufferedImage src,BufferedImage dest){
  int[] histogram = new int[256];
  int width = src.getWidth();
  int height = src.getHeight();
  if(dest == null){
  dest = creatCompatibleDestImage(src,null);
  }
  int[] inPixels = new int[width*height];
  getRGB(src,0,0,width,height,inPixels);

  //獲取直方圖數據
  for(int i=0;i<histogram.length;i++){
      histogram[i] = 0;
  }
  int index = 0;
  for(int row=0;row<height;row++){
      int tr = 0;
      for(int col=0;col<width;col++){
          index = row*width+col;
          tr = (inPixels[index] >> 16) & 0xff;
          histogram[tr] ++;
      }
  }
  double maxFrequency = 0;//計算像素出現的最大頻率值
  for(int i=0;i<histogram.length;i++){
      maxFrequency = Math.max(histogram[i],maxFrequency);
  }
  //繪制直方圖
  Graphics2D g2d = dest.createGraphics();
  g2d.setPaint(Color.LIGHT_GRAY);
  g2d.fillRect(0,0,width,height);
  
  //繪制XY軸
  g2d.setPaint(Color.black);
  g2d.drawLine(50,50,50,height-50);
  g2d.drawLine(50,height-50,width-50,height-50);
  //繪制XY軸標題
  g2d.drawString("0",50,height-30);
  g2d.drawString("255",width-50,height-30);
  g2d.drawString("0",20,height-50);
  g2d.drawString(""+maxFrequency,20,50);
  //繪制坐標軸刻度
  double xunit = (width-100)/255;
  double yunit = (height-100)/maxFrequency;
  for(int i=0;i<histogram.length;i++){
      double xp = 50+xunit*i;
      double yp = yunit*histogram[i];
      Rectangle2D rect2d = new Rectangle2D.Double(xp,height-50-yp,xunit,yp);
      g2d.fill(rect2d);
  }
  System.out.print(maxFrequency);
  return dest;
   
  

  }

}
測試代碼同上

灰度圖像的直方圖