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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.

5. Please read this Source Code License Agreement carefully before using

6. the source code.

8. Adobe Systems Incorporated grants to you a perpetual, worldwide, non-exclusive,

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15. derived from the source code without prior written permission.

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20. code.

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

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28. EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

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31. WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR

32. OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOURCE CODE, EVEN IF

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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;

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. }

87. private static var crcTable:Array;

88. private static var crcTableComputed:Boolean = false;

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. }

如何使用：

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．