Png图片换色的方法

昨天研究了BB同志发的算法一文，实验了一晚上，终于有点收获，发出来给大家共享．

我查阅了很多关于Png格式的文章，最后得到的心得就是，对于＂索引类型的图片＂，即肯定包含PLTE调色板的Png图片，就可以通过对调色板的修改，再通过CRC算法生成新的验证码，再还原成新图片就可以得到所要的效果，为此，我写了如下的类．

/*
 用于PNG图片变色的类
 使用要求，需要美工将原始图片的需要换色的点
 设置为纯红色0xff0000
 */
import java.io.*;
import java.lang.*;
import javax.microedition.lcdui.*;

public class coloredImage {
    public coloredImage() {
    }

    public Image getColoredImage(String s, int newcolor) {
        try {
            byte[] pixel;
            InputStream is = getClass().getResourceAsStream(s);
            int i = 0;
            while (is.read() != -1) {
                i++;
            }
            pixel = new byte[i];
            is = null;
            is = getClass().getResourceAsStream(s);
            is.read(pixel);
            imgConvert(pixel, newcolor);
            return (Image.createImage(pixel, 0, pixel.length));
        } catch (Exception e) {
            return null;
        }
    }

    public void imgConvert(byte content[], int color) {
        try {
            int start = 0;
            int newcolor = -1;
            for (int idx = 0; idx < 8; idx++) {
                if (content[idx] == 0x50 && content[idx + 1] == 0x4c
                    && content[idx + 2] == 0x54 && content[idx + 3] == 0x45) {
                    start = idx;
                }
            }
            for (int idx = 0; idx < 4; idx++) {
                newcolor = pixelConvert(content[start + idx], newcolor);
            }
            int r, g, b, length;
            length = (content[start - 4] & 0xff << 24) |
                     (content[start - 3] & 0xff << 16) |
                     (content[start - 2] & 0xff << 8) |
                     (content[start - 1] & 0xff);
            for (int i = 0; i < length; i++) {
                r = content[start + 4 + i] & 0xff;
                g = content[start + 4 + i + 1] & 0xff;
                b = content[start + 4 + i + 2] & 0xff;
                if (r == 255 && g == 0 && b == 0) {
                    r = color >> 16 & 0xff;
                    g = color >> 8 & 0xff;
                    b = color & 0xff;
                    content[start + 4 + i] = (byte) r;
                    content[start + 4 + i + 1] = (byte) g;
                    content[start + 4 + i + 2] = (byte) b;
                }
                newcolor = pixelConvert(content[start + 4 + i], newcolor);
                newcolor = pixelConvert(content[start + 4 + i + 1], newcolor);
                newcolor = pixelConvert(content[start + 4 + i + 2], newcolor);
            }
            newcolor = ~newcolor;
            content[start + 4 + length] = (byte) (newcolor >> 24);
            content[start + 4 + length + 1] = (byte) (newcolor >> 16);
            content[start + 4 + length + 2] = (byte) (newcolor >> 8);
            content[start + 4 + length + 3] = (byte) (newcolor);
        } catch (Exception e) {}
    }

    /**
     * CRC检验算法
     * @param pixel 像素
     * @param color 颜色值
     * @return
     */
    public int pixelConvert(byte pixel, int color) {
        int tmp = pixel & 0xff;
        color ^= tmp;
        for (int idx = 0; idx < 8; idx++) {
            if ((color & 1) != 0) {
                color = color >>> 1 ^ 0xedb88320;
            } else {
                color >>>= 1;
            }
        }
        return color;
    }
}

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.*;
import com.nokia.mid.ui.*;
import java.io.*;

public class pengzhuang extends MIDlet {
    class test extends FullCanvas {
        Image[] a;
        byte[] pix;
        coloredImage ci;
        public test() {
            ci = new coloredImage();
            a = new Image[4];
            a[0] = ci.getColoredImage("/char.png", 0x0000ff);
            a[1] = ci.getColoredImage("/char.png", 0x00ff00);
            a[2] = ci.getColoredImage("/char.png", 0xffffff);
            a[3] = ci.getColoredImage("/char.png", 0x00ffff);
        }

        public void keyPressed(int i) {
        }

        public void paint(Graphics g) {
            g.setColor(0xffffff);
            g.fillRect(0, 0, getWidth(), getHeight());
            g.drawImage(a[0], 0, 0, 0);
            g.drawImage(a[1], 30, 30, 0);
            g.drawImage(a[2], 60, 60, 0);
            g.drawImage(a[3], 90, 90, 0);
        }
    }


    private Display display;
    test t;
    public pengzhuang() {
        try {
            t = new test();
        } catch (Exception e) {
        }
        display = Display.getDisplay(this);
    }

    public void startApp() {
        display.setCurrent(t);
    }

    public void pauseApp() {

    }

    public void destroyApp(boolean boo) {

    }
}

其中用到的源图是

运行程序后的效果为