source

 
var jpegEnc:JPEGEncoder(75); // quality
var jpegDat:ByteArray = jpegEnc.encode(myBitmapData);
 
package {
	import flash.geom.*;
	import flash.display.*;
	import flash.util.*;
 
	public class BitString {
		public var len:int = 0;
		public var val:int = 0;
	};
 
	public class JPEGEncoder
	{
 
		// Static table initialization
 
		private var ZigZag:Array = [
			 0, 1, 5, 6,14,15,27,28,
			 2, 4, 7,13,16,26,29,42,
			 3, 8,12,17,25,30,41,43,
			 9,11,18,24,31,40,44,53,
			10,19,23,32,39,45,52,54,
			20,22,33,38,46,51,55,60,
			21,34,37,47,50,56,59,61,
			35,36,48,49,57,58,62,63
		];
 
		private var YTable:Array = new Array(64);
		private var UVTable:Array = new Array(64);
		private var fdtbl_Y:Array = new Array(64);
		private var fdtbl_UV:Array = new Array(64);
 
		private function initQuantTables(sf:int):Void
		{
			var YQT:Array = [
				16, 11, 10, 16, 24, 40, 51, 61,
				12, 12, 14, 19, 26, 58, 60, 55,
				14, 13, 16, 24, 40, 57, 69, 56,
				14, 17, 22, 29, 51, 87, 80, 62,
				18, 22, 37, 56, 68,109,103, 77,
				24, 35, 55, 64, 81,104,113, 92,
				49, 64, 78, 87,103,121,120,101,
				72, 92, 95, 98,112,100,103, 99
			];
			for (var i:int = 0; i < 64; i++) {
				var t:Number = Math.floor((YQT[i]*sf+50)/100);
				if (t < 1) {
					t = 1;
				} else if (t > 255) {
					t = 255;
				}
				YTable[ZigZag[i]] = t;
			}
			var UVQT:Array = [
				17, 18, 24, 47, 99, 99, 99, 99,
				18, 21, 26, 66, 99, 99, 99, 99,
				24, 26, 56, 99, 99, 99, 99, 99,
				47, 66, 99, 99, 99, 99, 99, 99,
				99, 99, 99, 99, 99, 99, 99, 99,
				99, 99, 99, 99, 99, 99, 99, 99,
				99, 99, 99, 99, 99, 99, 99, 99,
				99, 99, 99, 99, 99, 99, 99, 99
			];
			for (var i:int = 0; i < 64; i++) {
				var t:Number = Math.floor((UVQT[i]*sf+50)/100);
				if (t < 1) {
					t = 1;
				} else if (t > 255) {
					t = 255;
				}
				UVTable[ZigZag[i]] = t;
			}
			var aasf:Array = [
				1.0, 1.387039845, 1.306562965, 1.175875602,
				1.0, 0.785694958, 0.541196100, 0.275899379
			];
			var i:int = 0;
			for (var row:int = 0; row < 8; row++)
			{
				for (var col:int = 0; col < 8; col++)
				{
					fdtbl_Y[i]  = (1.0 / (YTable [ZigZag[i]] * aasf[row] * aasf[col] * 8.0));
					fdtbl_UV[i] = (1.0 / (UVTable[ZigZag[i]] * aasf[row] * aasf[col] * 8.0));
					i++;
				}
			}
		}
 
		private var YDC_HT:Array;
		private var UVDC_HT:Array;
		private var YAC_HT:Array;
		private var UVAC_HT:Array;
 
		private function computeHuffmanTbl(nrcodes:Array, std_table:Array):Array
		{
			var codevalue:int = 0;
			var pos_in_table:int = 0;
			var HT:Array = new Array();
			for (var k:int=1; k<=16; k++) {
				for (var j:int=1; j<=nrcodes[k]; j++) {
					HT[std_table[pos_in_table]] = new BitString();
					HT[std_table[pos_in_table]].val = codevalue;
					HT[std_table[pos_in_table]].len = k;
					pos_in_table++;
					codevalue++;
				}
				codevalue*=2;
			}
			return HT;
		}
 
		private var std_dc_luminance_nrcodes:Array = [0,0,1,5,1,1,1,1,1,1,0,0,0,0,0,0,0];
		private var std_dc_luminance_values:Array = [0,1,2,3,4,5,6,7,8,9,10,11];
		private var std_ac_luminance_nrcodes:Array = [0,0,2,1,3,3,2,4,3,5,5,4,4,0,0,1,0x7d];
		private var std_ac_luminance_values:Array = [
			0x01,0x02,0x03,0x00,0x04,0x11,0x05,0x12,
			0x21,0x31,0x41,0x06,0x13,0x51,0x61,0x07,
			0x22,0x71,0x14,0x32,0x81,0x91,0xa1,0x08,
			0x23,0x42,0xb1,0xc1,0x15,0x52,0xd1,0xf0,
			0x24,0x33,0x62,0x72,0x82,0x09,0x0a,0x16,
			0x17,0x18,0x19,0x1a,0x25,0x26,0x27,0x28,
			0x29,0x2a,0x34,0x35,0x36,0x37,0x38,0x39,
			0x3a,0x43,0x44,0x45,0x46,0x47,0x48,0x49,
			0x4a,0x53,0x54,0x55,0x56,0x57,0x58,0x59,
			0x5a,0x63,0x64,0x65,0x66,0x67,0x68,0x69,
			0x6a,0x73,0x74,0x75,0x76,0x77,0x78,0x79,
			0x7a,0x83,0x84,0x85,0x86,0x87,0x88,0x89,
			0x8a,0x92,0x93,0x94,0x95,0x96,0x97,0x98,
			0x99,0x9a,0xa2,0xa3,0xa4,0xa5,0xa6,0xa7,
			0xa8,0xa9,0xaa,0xb2,0xb3,0xb4,0xb5,0xb6,
			0xb7,0xb8,0xb9,0xba,0xc2,0xc3,0xc4,0xc5,
			0xc6,0xc7,0xc8,0xc9,0xca,0xd2,0xd3,0xd4,
			0xd5,0xd6,0xd7,0xd8,0xd9,0xda,0xe1,0xe2,
			0xe3,0xe4,0xe5,0xe6,0xe7,0xe8,0xe9,0xea,
			0xf1,0xf2,0xf3,0xf4,0xf5,0xf6,0xf7,0xf8,
			0xf9,0xfa
		];
 
		private var std_dc_chrominance_nrcodes:Array = [0,0,3,1,1,1,1,1,1,1,1,1,0,0,0,0,0];
		private var std_dc_chrominance_values:Array = [0,1,2,3,4,5,6,7,8,9,10,11];
		private var std_ac_chrominance_nrcodes:Array = [0,0,2,1,2,4,4,3,4,7,5,4,4,0,1,2,0x77];
		private var std_ac_chrominance_values:Array = [
			0x00,0x01,0x02,0x03,0x11,0x04,0x05,0x21,
			0x31,0x06,0x12,0x41,0x51,0x07,0x61,0x71,
			0x13,0x22,0x32,0x81,0x08,0x14,0x42,0x91,
			0xa1,0xb1,0xc1,0x09,0x23,0x33,0x52,0xf0,
			0x15,0x62,0x72,0xd1,0x0a,0x16,0x24,0x34,
			0xe1,0x25,0xf1,0x17,0x18,0x19,0x1a,0x26,
			0x27,0x28,0x29,0x2a,0x35,0x36,0x37,0x38,
			0x39,0x3a,0x43,0x44,0x45,0x46,0x47,0x48,
			0x49,0x4a,0x53,0x54,0x55,0x56,0x57,0x58,
			0x59,0x5a,0x63,0x64,0x65,0x66,0x67,0x68,
			0x69,0x6a,0x73,0x74,0x75,0x76,0x77,0x78,
			0x79,0x7a,0x82,0x83,0x84,0x85,0x86,0x87,
			0x88,0x89,0x8a,0x92,0x93,0x94,0x95,0x96,
			0x97,0x98,0x99,0x9a,0xa2,0xa3,0xa4,0xa5,
			0xa6,0xa7,0xa8,0xa9,0xaa,0xb2,0xb3,0xb4,
			0xb5,0xb6,0xb7,0xb8,0xb9,0xba,0xc2,0xc3,
			0xc4,0xc5,0xc6,0xc7,0xc8,0xc9,0xca,0xd2,
			0xd3,0xd4,0xd5,0xd6,0xd7,0xd8,0xd9,0xda,
			0xe2,0xe3,0xe4,0xe5,0xe6,0xe7,0xe8,0xe9,
			0xea,0xf2,0xf3,0xf4,0xf5,0xf6,0xf7,0xf8,
			0xf9,0xfa
		];
 
		private function initHuffmanTbl():Void
		{
			YDC_HT = computeHuffmanTbl(std_dc_luminance_nrcodes,std_dc_luminance_values);
			UVDC_HT = computeHuffmanTbl(std_dc_chrominance_nrcodes,std_dc_chrominance_values);
			YAC_HT = computeHuffmanTbl(std_ac_luminance_nrcodes,std_ac_luminance_values);
			UVAC_HT = computeHuffmanTbl(std_ac_chrominance_nrcodes,std_ac_chrominance_values);
		}
 
		private var bitcode:Array = new Array(65535);
		private var category:Array = new Array(65535);
 
		private function initCategoryNumber()
		{
			var nrlower:int = 1;
			var nrupper:int = 2;
			for (var cat:int=1; cat<=15; cat++) {
				//Positive numbers
				for (var nr:int=nrlower; nr<nrupper; nr++) {
					category[32767+nr] = cat;
					bitcode[32767+nr] = new BitString();
					bitcode[32767+nr].len = cat;
					bitcode[32767+nr].val = nr;
				}
				//Negative numbers
				for (var nr:int=-(nrupper-1); nr<=-nrlower; nr++) {
					category[32767+nr] = cat;
					bitcode[32767+nr] = new BitString();
					bitcode[32767+nr].len = cat;
					bitcode[32767+nr].val = nrupper-1+nr;
				}
				nrlower <<= 1;
				nrupper <<= 1;
			}
		}
 
		// IO functions
 
		private var byteout:ByteArray;
		private var bytenew:int = 0;
		private var bytepos:int = 7;
 
		private function writeBits(bs:BitString):Void
		{
			var value:int = bs.val;
			var posval:int = bs.len-1;
			while ( posval >= 0 ) {
				if (value & uint(1 << posval) ) {
					bytenew |= uint(1 << bytepos);
				}
				posval--;
				bytepos--;
				if (bytepos < 0) {
					if (bytenew == 0xFF) {
						writeByte(0xFF);
						writeByte(0);
					}
					else {
						writeByte(bytenew);
					}
					bytepos=7;
					bytenew=0;
				}
			}
		}
 
		private function writeByte(value:int)
		{
			byteout.writeByte(value);
		}
 
		private function writeWord(value:int)
		{
			writeByte((value>>8)&0xFF);
			writeByte((value   )&0xFF);
		}
 
		// DCT & quantization core
 
		private function fDCTQuant(data:Array, fdtbl:Array):Array
		{
			/* Pass 1: process rows. */
			var dataOff:int=0;
			for (var i:int=0; i<8; i++) {
				var tmp0:Number = data[dataOff+0] + data[dataOff+7];
				var tmp7:Number = data[dataOff+0] - data[dataOff+7];
				var tmp1:Number = data[dataOff+1] + data[dataOff+6];
				var tmp6:Number = data[dataOff+1] - data[dataOff+6];
				var tmp2:Number = data[dataOff+2] + data[dataOff+5];
				var tmp5:Number = data[dataOff+2] - data[dataOff+5];
				var tmp3:Number = data[dataOff+3] + data[dataOff+4];
				var tmp4:Number = data[dataOff+3] - data[dataOff+4];
 
				/* Even part */
				var tmp10:Number = tmp0 + tmp3;	/* phase 2 */
				var tmp13:Number = tmp0 - tmp3;
				var tmp11:Number = tmp1 + tmp2;
				var tmp12:Number = tmp1 - tmp2;
 
				data[dataOff+0] = tmp10 + tmp11; /* phase 3 */
				data[dataOff+4] = tmp10 - tmp11;
 
				var z1:Number = (tmp12 + tmp13) * 0.707106781; /* c4 */
				data[dataOff+2] = tmp13 + z1; /* phase 5 */
				data[dataOff+6] = tmp13 - z1;
 
				/* Odd part */
				tmp10 = tmp4 + tmp5; /* phase 2 */
				tmp11 = tmp5 + tmp6;
				tmp12 = tmp6 + tmp7;
 
				/* The rotator is modified from fig 4-8 to avoid extra negations. */
				var z5:Number = (tmp10 - tmp12) * 0.382683433; /* c6 */
				var z2:Number = 0.541196100 * tmp10 + z5; /* c2-c6 */
				var z4:Number = 1.306562965 * tmp12 + z5; /* c2+c6 */
				var z3:Number = tmp11 * 0.707106781; /* c4 */
 
				var z11:Number = tmp7 + z3;	/* phase 5 */
				var z13:Number = tmp7 - z3;
 
				data[dataOff+5] = z13 + z2;	/* phase 6 */
				data[dataOff+3] = z13 - z2;
				data[dataOff+1] = z11 + z4;
				data[dataOff+7] = z11 - z4;
 
				dataOff += 8; /* advance pointer to next row */
			}
 
			/* Pass 2: process columns. */
			dataOff = 0;
			for (var i:int=0; i<8; i++) {
				var tmp0:Number = data[dataOff+ 0] + data[dataOff+56];
				var tmp7:Number = data[dataOff+ 0] - data[dataOff+56];
				var tmp1:Number = data[dataOff+ 8] + data[dataOff+48];
				var tmp6:Number = data[dataOff+ 8] - data[dataOff+48];
				var tmp2:Number = data[dataOff+16] + data[dataOff+40];
				var tmp5:Number = data[dataOff+16] - data[dataOff+40];
				var tmp3:Number = data[dataOff+24] + data[dataOff+32];
				var tmp4:Number = data[dataOff+24] - data[dataOff+32];
 
				/* Even part */
				var tmp10:Number = tmp0 + tmp3;	/* phase 2 */
				var tmp13:Number = tmp0 - tmp3;
				var tmp11:Number = tmp1 + tmp2;
				var tmp12:Number = tmp1 - tmp2;
 
				data[dataOff+ 0] = tmp10 + tmp11; /* phase 3 */
				data[dataOff+32] = tmp10 - tmp11;
 
				var z1:Number = (tmp12 + tmp13) * 0.707106781; /* c4 */
				data[dataOff+16] = tmp13 + z1; /* phase 5 */
				data[dataOff+48] = tmp13 - z1;
 
				/* Odd part */
				tmp10 = tmp4 + tmp5; /* phase 2 */
				tmp11 = tmp5 + tmp6;
				tmp12 = tmp6 + tmp7;
 
				/* The rotator is modified from fig 4-8 to avoid extra negations. */
				var z5:Number = (tmp10 - tmp12) * 0.382683433; /* c6 */
				var z2:Number = 0.541196100 * tmp10 + z5; /* c2-c6 */
				var z4:Number = 1.306562965 * tmp12 + z5; /* c2+c6 */
				var z3:Number= tmp11 * 0.707106781; /* c4 */
 
				var z11:Number = tmp7 + z3;	/* phase 5 */
				var z13:Number = tmp7 - z3;
 
				data[dataOff+40] = z13 + z2; /* phase 6 */
				data[dataOff+24] = z13 - z2;
				data[dataOff+ 8] = z11 + z4;
				data[dataOff+56] = z11 - z4;
 
				dataOff++; /* advance pointer to next column */
			}
 
			// Quantize/descale the coefficients
			for (var i:int=0; i<64; i++) {
				// Apply the quantization and scaling factor & Round to nearest integer
				data[i] = Math.round((data[i]*fdtbl[i]));
			}
			return data;
		}
 
		// Chunk writing
 
		private function writeAPP0():Void
		{
			writeWord(0xFFE0); // marker
			writeWord(16); // length
			writeByte(0x4A); // J
			writeByte(0x46); // F
			writeByte(0x49); // I
			writeByte(0x46); // F
			writeByte(0); // = "JFIF",'\0'
			writeByte(1); // versionhi
			writeByte(1); // versionlo
			writeByte(0); // xyunits
			writeWord(1); // xdensity
			writeWord(1); // ydensity
			writeByte(0); // thumbnwidth
			writeByte(0); // thumbnheight
		}
 
		private function writeSOF0(width:int, height:int):Void
		{
			writeWord(0xFFC0); // marker
			writeWord(17);   // length, truecolor YUV JPG
			writeByte(8);    // precision
			writeWord(height);
			writeWord(width);
			writeByte(3);    // nrofcomponents
			writeByte(1);    // IdY
			writeByte(0x11); // HVY
			writeByte(0);    // QTY
			writeByte(2);    // IdU
			writeByte(0x11); // HVU
			writeByte(1);    // QTU
			writeByte(3);    // IdV
			writeByte(0x11); // HVV
			writeByte(1);    // QTV
		}
 
		private function writeDQT():Void
		{
			writeWord(0xFFDB); // marker
			writeWord(132);	   // length
			writeByte(0);
			for (var i:int=0; i<64; i++) {
				writeByte(YTable[i]);
			}
			writeByte(1);
			for (var i:int=0; i<64; i++) {
				writeByte(UVTable[i]);
			}
		}
 
		private function writeDHT():Void
		{
			writeWord(0xFFC4); // marker
			writeWord(0x01A2); // length
 
			writeByte(0); // HTYDCinfo
			for (var i:int=0; i<16; i++) {
				writeByte(std_dc_luminance_nrcodes[i+1]);
			}
			for (var i:int=0; i<=11; i++) {
				writeByte(std_dc_luminance_values[i]);
			}
 
			writeByte(0x10); // HTYACinfo
			for (var i:int=0; i<16; i++) {
				writeByte(std_ac_luminance_nrcodes[i+1]);
			}
			for (var i:int=0; i<=161; i++) {
				writeByte(std_ac_luminance_values[i]);
			}
 
			writeByte(1); // HTUDCinfo
			for (var i:int=0; i<16; i++) {
				writeByte(std_dc_chrominance_nrcodes[i+1]);
			}
			for (var i:int=0; i<=11; i++) {
				writeByte(std_dc_chrominance_values[i]);
			}
 
			writeByte(0x11); // HTUACinfo
			for (var i:int=0; i<16; i++) {
				writeByte(std_ac_chrominance_nrcodes[i+1]);
			}
			for (var i:int=0; i<=161; i++) {
				writeByte(std_ac_chrominance_values[i]);
			}
		}
 
		private function writeSOS():Void
		{
			writeWord(0xFFDA); // marker
			writeWord(12); // length
			writeByte(3); // nrofcomponents
			writeByte(1); // IdY
			writeByte(0); // HTY
			writeByte(2); // IdU
			writeByte(0x11); // HTU
			writeByte(3); // IdV
			writeByte(0x11); // HTV
			writeByte(0); // Ss
			writeByte(0x3f); // Se
			writeByte(0); // Bf
		}
 
		// Core processing
		var DU:Array = new Array(64);
 
		private function processDU(CDU:Array, fdtbl:Array, DC:Number, HTDC:Array, HTAC:Array):Number
		{
			var EOB:BitString = HTAC[0x00];
			var M16zeroes:BitString = HTAC[0xF0];
 
			var DU_DCT:Array = fDCTQuant(CDU, fdtbl);
			//ZigZag reorder
			for (var i:int=0;i<64;i++) {
				DU[ZigZag[i]]=DU_DCT[i];
			}
			var Diff:int = DU[0] - DC; DC = DU[0];
			//Encode DC
			if (Diff==0) {
				writeBits(HTDC[0]); // Diff might be 0
			} else {
				writeBits(HTDC[category[32767+Diff]]);
				writeBits(bitcode[32767+Diff]);
			}
			//Encode ACs
			var end0pos:int = 63;
			for (; (end0pos>0)&&(DU[end0pos]==0); end0pos--) {
			};
			//end0pos = first element in reverse order !=0
			if ( end0pos == 0) {
				writeBits(EOB);
				return DC;
			}
			var i:int = 1;
			while ( i <= end0pos ) {
				var startpos:int = i;
				for (; (DU[i]==0) && (i<=end0pos); i++) {
				}
				var nrzeroes:int = i-startpos;
				if ( nrzeroes >= 16 ) {
					for (var nrmarker:int=1; nrmarker <= nrzeroes/16; nrmarker++) {
						writeBits(M16zeroes);
					}
					nrzeroes = int(nrzeroes&0xF);
				}
				writeBits(HTAC[nrzeroes*16+category[32767+DU[i]]]);
				writeBits(bitcode[32767+DU[i]]);
				i++;
			}
			if ( end0pos != 63 ) {
				writeBits(EOB);
			}
			return DC;
		}
 
		private var YDU:Array = new Array(64);
		private var UDU:Array = new Array(64);
		private var VDU:Array = new Array(64);
 
		private function RGB2YUV(img:BitmapData, xpos:int, ypos:int)
		{
			var pos:int=0;
			for (var y:int=0; y<8; y++) {
				for (var x:int=0; x<8; x++) {
					var P:uint = img.getPixel32(xpos+x,ypos+y);
					var R:Number = Number((P>>16)&0xFF);
					var G:Number = Number((P>> 8)&0xFF);
					var B:Number = Number((P    )&0xFF);
					YDU[pos]=((( 0.29900)*R+( 0.58700)*G+( 0.11400)*B))-128;
					UDU[pos]=(((-0.16874)*R+(-0.33126)*G+( 0.50000)*B));
					VDU[pos]=((( 0.50000)*R+(-0.41869)*G+(-0.08131)*B));
					pos++;
				}
			}
		}
 
		public function JPEGEncoder(quality:Number = 50)
		{
			if (quality <= 0) {
				quality = 1;
			}
			if (quality > 100) {
				quality = 100;
			}
			var sf:int = 0;
			if (quality < 50) {
				sf = int(5000 / quality);
			} else {
				sf = int(200 - quality*2);
			}
			// Create tables
			initHuffmanTbl();
			initCategoryNumber();
			initQuantTables(sf);
		}
 
		public function encode(image:BitmapData):ByteArray
		{
			// Initialize bit writer
			byteout = new ByteArray();
			bytenew=0;
			bytepos=7;
 
			// Add JPEG headers
			writeWord(0xFFD8); // SOI
			writeAPP0();
			writeDQT();
			writeSOF0(image.width,image.height);
			writeDHT();
			writeSOS();
 
			// Encode 8x8 macroblocks
			var DCY:Number=0;
			var DCU:Number=0;
			var DCV:Number=0;
			bytenew=0;
			bytepos=7;
			for (var ypos:int=0; ypos<image.height; ypos+=8) {
				for (var xpos:int=0; xpos<image.width; xpos+=8) {
					RGB2YUV(image, xpos, ypos);
					DCY = processDU(YDU, fdtbl_Y, DCY, YDC_HT, YAC_HT);
					DCU = processDU(UDU, fdtbl_UV, DCU, UVDC_HT, UVAC_HT);
					DCV = processDU(VDU, fdtbl_UV, DCV, UVDC_HT, UVAC_HT);
				}
			}
 
			// Do the bit alignment of the EOI marker
			if ( bytepos >= 0 ) {
				var fillbits:BitString = new BitString();
				fillbits.len = bytepos+1;
				fillbits.val = (1<<(bytepos+1))-1;
				writeBits(fillbits);
			}
 
			writeWord(0xFFD9); //EOI
			return byteout;
		}
	}
}

source

var myPNG:ByteArray = PNGEnc.encode(myBitmapData);
 
import flash.geom.*;
import flash.display.*;
import flash.util.*;
 
public class PNGEnc {
 
    public static function encode(img:BitmapData):ByteArray {
        // Create output byte array
        var png:ByteArray = new ByteArray();
        // Write PNG signature
        png.writeUnsignedInt(0x89504e47);
        png.writeUnsignedInt(0x0D0A1A0A);
        // Build IHDR chunk
        var IHDR:ByteArray = new ByteArray();
        IHDR.writeInt(img.width);
        IHDR.writeInt(img.height);
        IHDR.writeUnsignedInt(0x08060000); // 32bit RGBA
        IHDR.writeByte(0);
        writeChunk(png,0x49484452,IHDR);
        // Build IDAT chunk
        var IDAT:ByteArray= new ByteArray();
        for(var i:int=0;i < img.height;i++) {
            // no filter
            IDAT.writeByte(0);
            var p:uint;
            if ( !img.transparent ) {
                for(var j:int=0;j < img.width;j++) {
                    p = img.getPixel(j,i);
                    IDAT.writeUnsignedInt(
                        uint(((p&0xFFFFFF) << 8)|0xFF));
                }
            } else {
                for(var j:int=0;j < img.width;j++) {
                    p = img.getPixel32(j,i);
                    IDAT.writeUnsignedInt(
                        uint(((p&0xFFFFFF) << 8)|
                        (shr(p,24))));
                }
            }
        }
        IDAT.compress();
        writeChunk(png,0x49444154,IDAT);
        // Build IEND chunk
        writeChunk(png,0x49454E44,null);
        // return PNG
        return png;
    }
 
    private static var crcTable:Array;
    private static var crcTableComputed:Boolean = false;
 
    private static function writeChunk(png:ByteArray, 
            type:uint, data:ByteArray) {
        if (!crcTableComputed) {
            crcTableComputed = true;
            crcTable = [];
            for (var n:uint = 0; n < 256; n++) {
                var c:uint = n;
                for (var k:uint = 0; k < 8; k++) {
                    if (c & 1) {
                        c = uint(uint(0xedb88320) ^ 
                            uint(c >>> 1));
                    } else {
                        c = uint(c >>> 1);
                    }
                }
                crcTable[n] = c;
            }
        }
        var len:uint = 0;
        if (data != null) {
            len = data.length;
        }
        png.writeUnsignedInt(len);
        var p:uint = png.position;
        png.writeUnsignedInt(type);
        if ( data != null ) {
            png.writeBytes(data);
        }
        var e:uint = png.position;
        png.position = p;
        var c:uint = 0xffffffff;
        for (var i:int = 0; i < (e-p); i++) {
            c = uint(crcTable[
                (c ^ png.readUnsignedByte()) & 
                uint(0xff)] ^ uint(c >>> 8));
        }
        c = uint(c^uint(0xffffffff));
        png.position = e;
        png.writeUnsignedInt(c);
    }
}