From: http://www.jamesward.com/wordpress/2006/08/16/flex-paint-flex-display-object-to-png/
关于AS3的png图片编码器：
代码如下：

1. /*
2. Adobe Systems Incorporated(r) Source Code License Agreement
3. Copyright(c) 2005 Adobe Systems Incorporated. All rights reserved.
4.  
5. Please read this Source Code License Agreement carefully before using
6. the source code.
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11. distribute this source code and such derivative works in source or
12. object code form without any attribution requirements. 
13.  
14. The name "Adobe Systems Incorporated" must not be used to endorse or promote products
15. derived from the source code without prior written permission.
16.  
17. You agree to indemnify, hold harmless and defend Adobe Systems Incorporated from and
18. against any loss, damage, claims or lawsuits, including attorney's
19. fees that arise or result from your use or distribution of the source
20. code.
21.  
22. THIS SOURCE CODE IS PROVIDED "AS IS" AND "WITH ALL FAULTS", WITHOUT
23. ANY TECHNICAL SUPPORT or ANY EXPRESSED or IMPLIED WARRANTIES, INCLUDING,
24. BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
25. FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  ALSO, THERE IS NO WARRANTY OF
26. NON-INFRINGEMENT, TITLE or QUIET ENJOYMENT.  IN NO EVENT SHALL MACROMEDIA
27. OR ITS SUPPLIERS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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34. */
35. package com.adobe.images
36. {
37. import flash.geom.*;
38. import flash.display.Bitmap;
39. import flash.display.BitmapData;
40. import flash.utils.ByteArray;
41.  
42. public class PNGEncoder
43. {
44.     public static function encode(img:BitmapData):ByteArray {
45.         // Create output byte array
46.         var png:ByteArray = new ByteArray();
47.         // Write PNG signature
48.         png.writeUnsignedInt(0x89504e47);
49.         png.writeUnsignedInt(0x0D0A1A0A);
50.         // Build IHDR chunk
51.         var IHDR:ByteArray = new ByteArray();
52.         IHDR.writeInt(img.width);
53.         IHDR.writeInt(img.height);
54.         IHDR.writeUnsignedInt(0x08060000); // 32bit RGBA
55.         IHDR.writeByte(0);
56.         writeChunk(png,0x49484452,IHDR);
57.         // Build IDAT chunk
58.         var IDAT:ByteArray= new ByteArray();
59.         for(var i:int=0;i < img.height;i++) {
60.             // no filter
61.             IDAT.writeByte(0);
62.             var p:uint;
63.             var j:int;
64.             if ( !img.transparent ) {
65.                 for(j=0;j < img.width;j++) {
66.                     p = img.getPixel(j,i);
67.                     IDAT.writeUnsignedInt(
68.                         uint(((p&0xFFFFFF) << 8)|0xFF));
69.                 }
70.             } else {
71.                 for(j=0;j < img.width;j++) {
72.                     p = img.getPixel32(j,i);
73.                     IDAT.writeUnsignedInt(
74.                         uint(((p&0xFFFFFF) << 8)|
75.                         (p>>>24)));
76.                 }
77.             }
78.         }
79.         IDAT.compress();
80.         writeChunk(png,0x49444154,IDAT);
81.         // Build IEND chunk
82.         writeChunk(png,0x49454E44,null);
83.         // return PNG
84.         return png;
85.     }
86.  
87.     private static var crcTable:Array;
88.     private static var crcTableComputed:Boolean = false;
89.  
90.     private static function writeChunk(png:ByteArray,
91.             type:uint, data:ByteArray):void {
92.         if (!crcTableComputed) {
93.             crcTableComputed = true;
94.             crcTable = [];
95.             var c:uint;
96.             for (var n:uint = 0; n < 256; n++) {
97.                 c = n;
98.                 for (var k:uint = 0; k < 8; k++) {
99.                     if (c & 1) {
100.                         c = uint(uint(0xedb88320) ^
101.                             uint(c >>> 1));
102.                     } else {
103.                         c = uint(c >>> 1);
104.                     }
105.                 }
106.                 crcTable[n] = c;
107.             }
108.         }
109.         var len:uint = 0;
110.         if (data != null) {
111.             len = data.length;
112.         }
113.         png.writeUnsignedInt(len);
114.         var p:uint = png.position;
115.         png.writeUnsignedInt(type);
116.         if ( data != null ) {
117.             png.writeBytes(data);
118.         }
119.         var e:uint = png.position;
120.         png.position = p;
121.         c = 0xffffffff;
122.         for (var i:int = 0; i < (e-p); i++) {
123.             c = uint(crcTable[
124.                 (c ^ png.readUnsignedByte()) &
125.                 uint(0xff)] ^ uint(c >>> 8));
126.         }
127.         c = uint(c^uint(0xffffffff));
128.         png.position = e;
129.         png.writeUnsignedInt(c);
130.     }
131. }
132. }

Flex Paint (需要Flash 9)

１、如图设置界面；
２、定义一个BitmapData 对象
　　　var bd:BitmapData = new BitmapData(canvas.width,canvas.height);　
３、将canvas中的像素拷贝到这个对象里
　　　bd.draw(canvas);
４、然后将BitmapData 转换成png格式的ByteArray 对象
５、将最后的png二进制传到服务器端保存．