read png file widrh and height

png_width_height

import java.io.*;
import java.net.URL;
import java.net.URLConnection;

public class Main {
    public static void main(String[] args) throws Exception {
        InputStream is;
        URL url = new URL("http://dribbble.com/system/users/1/screenshots/21603/shot_1274474082.png");
        URLConnection conn = url.openConnection();
        long start = System.currentTimeMillis();
        is = conn.getInputStream();
        long cost = System.currentTimeMillis() - start;
        System.out.println(cost+"ms");
        int w = 0;
        int h = 0;
        for (int i = 0; i < 24; i++) {
            int v = is.read();
            switch (i) {
                // image width chunk
                case 16:
                    w += v * 0x1000000;
                    break;
                case 17:
                    w += v * 0x10000;
                    break;
                case 18:
                    w += v * 0x100;
                    break;
                case 19:
                    w += v;
                    break;
                // image height chunk
                case 20:
                    h += v * 0x1000000;
                    break;
                case 21:
                    h += v * 0x10000;
                    break;
                case 22:
                    h += v * 0x100;
                    break;
                case 23:
                    h += v;
                    break;
                default:
                    break;
            }
        }
        System.out.println(w + "*" + h);
        is.close();
    }
}