BufferedImage的像素访问-内存泄漏？

Question

I want to build histograms from several images. To perform this process, I get access to the DataBufferByte I recognize that the GC doesn't free the memory after building the histogram. What is wrong with this code?

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.concurrent.atomic.AtomicInteger;
import javax.imageio.ImageIO;


public class Histogram {

    HashMap<Color,AtomicInteger> histogram;

    public Histogram() {
        histogram = new HashMap<>();
    }

    public void build(BufferedImage image){

        int pixelLength = 3;

        byte[] pixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();

        int red, green, blue;
        Color color;
        for ( int pixel = 0; pixel <= pixels.length - pixelLength; pixel+= pixelLength ) {

            blue= ((int) pixels[pixel] & 0xff); // blue
            green= (((int) pixels[pixel + 1] & 0xff) ); // green
            red = (((int) pixels[pixel + 2] & 0xff) ); // red
            color = new Color(red, green, blue);
            if(histogram.containsKey(color)){
                histogram.get(color).incrementAndGet();
            }
            else{
                histogram.put(color, new AtomicInteger(1));
            }
        }
        pixels = null;    
    }

    public static void main(String[] args) {
        String pathImage = "C://testjpg";
        try {
            for (int j = 0; j < 5000; j++) {
                BufferedImage i = ImageIO.read(new File(pathImage));

                Histogram h = new Histogram();

                h.build(i);
                i.flush();

            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }    
    }
}

thanks for your support :)

Answer 1

The GC does not run automatically and recalls the memory only when it needs it. You can force it using System.gc(), but be careful to not do it too often, else it will slow down your program.

Your code runs fine, and here is what I've tested:

public static void buildColorHistogram(BufferedImage image)
{
final int pixelLength = 3;

byte[] pixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();

for (int pixel=0 ; pixel < pixels.length; pixel+=pixelLength)
    {
    final int blue = pixels[pixel] & 0xff ; // blue
    final int green= pixels[pixel + 1] & 0xff ; // green
    final int red  = pixels[pixel + 2] & 0xff ; // red
    Color color = new Color(red, green, blue) ;
        if ( histogram.containsKey(color) )
            histogram.get(color).incrementAndGet() ;
        else
            histogram.put(color, new AtomicInteger(1)) ;
    }

pixels = null ;
}

Be careful that some color images have also an alpha channel, which means that pixelLength will be 4 instead of 3.

Do you empty out (flush) the histogram when you're done with it? Because there are 16 millions combinations/triplets of color.