jpg.js

/* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- /
/* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */
/*
   Copyright 2011 notmasteryet

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

// - The JPEG specification can be found in the ITU CCITT Recommendation T.81
//   (www.w3.org/Graphics/JPEG/itu-t81.pdf)
// - The JFIF specification can be found in the JPEG File Interchange Format
//   (www.w3.org/Graphics/JPEG/jfif3.pdf)
// - The Adobe Application-Specific JPEG markers in the Supporting the DCT Filters
//   in PostScript Level 2, Technical Note #5116
//   (partners.adobe.com/public/developer/en/ps/sdk/5116.DCT_Filter.pdf)

var JpegImage = (function jpegImage() {
  "use strict";
  var dctZigZag = new Int32Array([
     0,
     1,  8,
    16,  9,  2,
     3, 10, 17, 24,
    32, 25, 18, 11, 4,
     5, 12, 19, 26, 33, 40,
    48, 41, 34, 27, 20, 13,  6,
     7, 14, 21, 28, 35, 42, 49, 56,
    57, 50, 43, 36, 29, 22, 15,
    23, 30, 37, 44, 51, 58,
    59, 52, 45, 38, 31,
    39, 46, 53, 60,
    61, 54, 47,
    55, 62,
    63
  ]);

  var dctCos1  =  4017   // cos(pi/16)
  var dctSin1  =   799   // sin(pi/16)
  var dctCos3  =  3406   // cos(3*pi/16)
  var dctSin3  =  2276   // sin(3*pi/16)
  var dctCos6  =  1567   // cos(6*pi/16)
  var dctSin6  =  3784   // sin(6*pi/16)
  var dctSqrt2 =  5793   // sqrt(2)
  var dctSqrt1d2 = 2896  // sqrt(2) / 2

  function constructor() {
  }

  function buildHuffmanTable(codeLengths, values) {
    var k = 0, code = [], i, j, length = 16;
    while (length > 0 && !codeLengths[length - 1])
      length--;
    code.push({children: [], index: 0});
    var p = code[0], q;
    for (i = 0; i < length; i++) {
      for (j = 0; j < codeLengths[i]; j++) {
        p = code.pop();
        p.children[p.index] = values[k];
        while (p.index > 0) {
          p = code.pop();
        }
        p.index++;
        code.push(p);
        while (code.length <= i) {
          code.push(q = {children: [], index: 0});
          p.children[p.index] = q.children;
          p = q;
        }
        k++;
      }
      if (i + 1 < length) {
        // p here points to last code
        code.push(q = {children: [], index: 0});
        p.children[p.index] = q.children;
        p = q;
      }
    }
    return code[0].children;
  }

  function getBlockBufferOffset(component, row, col) {
    return 64 * ((component.blocksPerLine + 1) * row + col);
  }

  function decodeScan(data, offset,
                      frame, components, resetInterval,
                      spectralStart, spectralEnd,
                      successivePrev, successive) {
    var precision = frame.precision;
    var samplesPerLine = frame.samplesPerLine;
    var scanLines = frame.scanLines;
    var mcusPerLine = frame.mcusPerLine;
    var progressive = frame.progressive;
    var maxH = frame.maxH, maxV = frame.maxV;

    var startOffset = offset, bitsData = 0, bitsCount = 0;

    function readBit() {
      if (bitsCount > 0) {
        bitsCount--;
        return (bitsData >> bitsCount) & 1;
      }
      bitsData = data[offset++];
      if (bitsData == 0xFF) {
        var nextByte = data[offset++];
        if (nextByte) {
          throw "unexpected marker: " + ((bitsData << 8) | nextByte).toString(16);
        }
        // unstuff 0
      }
      bitsCount = 7;
      return bitsData >>> 7;
    }

    function decodeHuffman(tree) {
      var node = tree;
      var bit;
      while ((bit = readBit()) !== null) {
        node = node[bit];
        if (typeof node === 'number')
          return node;
        if (typeof node !== 'object')
          throw "invalid huffman sequence";
      }
      return null;
    }

    function receive(length) {
      var n = 0;
      while (length > 0) {
        var bit = readBit();
        if (bit === null) return;
        n = (n << 1) | bit;
        length--;
      }
      return n;
    }

    function receiveAndExtend(length) {
      var n = receive(length);
      if (n >= 1 << (length - 1))
        return n;
      return n + (-1 << length) + 1;
    }

    function decodeBaseline(component, offset) {
      var t = decodeHuffman(component.huffmanTableDC);
      var diff = t === 0 ? 0 : receiveAndExtend(t);
      component.blockData[offset] = (component.pred += diff);
      var k = 1;
      while (k < 64) {
        var rs = decodeHuffman(component.huffmanTableAC);
        var s = rs & 15, r = rs >> 4;
        if (s === 0) {
          if (r < 15)
            break;
          k += 16;
          continue;
        }
        k += r;
        var z = dctZigZag[k];
        component.blockData[offset + z] = receiveAndExtend(s);
        k++;
      }
    }

    function decodeDCFirst(component, offset) {
      var t = decodeHuffman(component.huffmanTableDC);
      var diff = t === 0 ? 0 : (receiveAndExtend(t) << successive);
      component.blockData[offset] = (component.pred += diff);
    }

    function decodeDCSuccessive(component, offset) {
      component.blockData[offset] |= readBit() << successive;
    }

    var eobrun = 0;
    function decodeACFirst(component, offset) {
      if (eobrun > 0) {
        eobrun--;
        return;
      }
      var k = spectralStart, e = spectralEnd;
      while (k <= e) {
        var rs = decodeHuffman(component.huffmanTableAC);
        var s = rs & 15, r = rs >> 4;
        if (s === 0) {
          if (r < 15) {
            eobrun = receive(r) + (1 << r) - 1;
            break;
          }
          k += 16;
          continue;
        }
        k += r;
        var z = dctZigZag[k];
        component.blockData[offset + z] = receiveAndExtend(s) * (1 << successive);
        k++;
      }
    }

    var successiveACState = 0, successiveACNextValue;
    function decodeACSuccessive(component, offset) {
      var k = spectralStart, e = spectralEnd, r = 0;
      while (k <= e) {
        var z = dctZigZag[k];
        switch (successiveACState) {
        case 0: // initial state
          var rs = decodeHuffman(component.huffmanTableAC);
          var s = rs & 15, r = rs >> 4;
          if (s === 0) {
            if (r < 15) {
              eobrun = receive(r) + (1 << r);
              successiveACState = 4;
            } else {
              r = 16;
              successiveACState = 1;
            }
          } else {
            if (s !== 1)
              throw "invalid ACn encoding";
            successiveACNextValue = receiveAndExtend(s);
            successiveACState = r ? 2 : 3;
          }
          continue;
        case 1: // skipping r zero items
        case 2:
          if (component.blockData[offset + z]) {
            component.blockData[offset + z] += (readBit() << successive);
          } else {
            r--;
            if (r === 0)
              successiveACState = successiveACState == 2 ? 3 : 0;
          }
          break;
        case 3: // set value for a zero item
          if (component.blockData[offset + z]) {
            component.blockData[offset + z] += (readBit() << successive);
          } else {
            component.blockData[offset + z] = successiveACNextValue << successive;
            successiveACState = 0;
          }
          break;
        case 4: // eob
          if (component.blockData[offset + z]) {
            component.blockData[offset + z] += (readBit() << successive);
          }
          break;
        }
        k++;
      }
      if (successiveACState === 4) {
        eobrun--;
        if (eobrun === 0)
          successiveACState = 0;
      }
    }

    function decodeMcu(component, decode, mcu, row, col) {
      var mcuRow = (mcu / mcusPerLine) | 0;
      var mcuCol = mcu % mcusPerLine;
      var blockRow = mcuRow * component.v + row;
      var blockCol = mcuCol * component.h + col;
      var offset = getBlockBufferOffset(component, blockRow, blockCol);
      decode(component, offset);
    }

    function decodeBlock(component, decode, mcu) {
      var blockRow = (mcu / component.blocksPerLine) | 0;
      var blockCol = mcu % component.blocksPerLine;
      var offset = getBlockBufferOffset(component, blockRow, blockCol);
      decode(component, offset);
    }

    var componentsLength = components.length;
    var component, i, j, k, n;
    var decodeFn;
    if (progressive) {
      if (spectralStart === 0)
        decodeFn = successivePrev === 0 ? decodeDCFirst : decodeDCSuccessive;
      else
        decodeFn = successivePrev === 0 ? decodeACFirst : decodeACSuccessive;
    } else {
      decodeFn = decodeBaseline;
    }

    var mcu = 0, marker;
    var mcuExpected;
    if (componentsLength == 1) {
      mcuExpected = components[0].blocksPerLine * components[0].blocksPerColumn;
    } else {
      mcuExpected = mcusPerLine * frame.mcusPerColumn;
    }
    if (!resetInterval) {
      resetInterval = mcuExpected;
    }

    var h, v;
    while (mcu < mcuExpected) {
      // reset interval stuff
      for (i = 0; i < componentsLength; i++) {
        components[i].pred = 0;
      }
      eobrun = 0;

      if (componentsLength == 1) {
        component = components[0];
        for (n = 0; n < resetInterval; n++) {
          decodeBlock(component, decodeFn, mcu);
          mcu++;
        }
      } else {
        for (n = 0; n < resetInterval; n++) {
          for (i = 0; i < componentsLength; i++) {
            component = components[i];
            h = component.h;
            v = component.v;
            for (j = 0; j < v; j++) {
              for (k = 0; k < h; k++) {
                decodeMcu(component, decodeFn, mcu, j, k);
              }
            }
          }
          mcu++;
        }
      }

      // find marker
      bitsCount = 0;
      marker = (data[offset] << 8) | data[offset + 1];
      if (marker <= 0xFF00) {
        throw "marker was not found";
      }

      if (marker >= 0xFFD0 && marker <= 0xFFD7) { // RSTx
        offset += 2;
      } else {
        break;
      }
    }

    return offset - startOffset;
  }

  // A port of poppler's IDCT method which in turn is taken from:
  //   Christoph Loeffler, Adriaan Ligtenberg, George S. Moschytz,
  //   "Practical Fast 1-D DCT Algorithms with 11 Multiplications",
  //   IEEE Intl. Conf. on Acoustics, Speech & Signal Processing, 1989,
  //   988-991.
  function quantizeAndInverse(component, blockBufferOffset, p) {
    var qt = component.quantizationTable;
    var v0, v1, v2, v3, v4, v5, v6, v7, t;
    var i;

    // dequant
    for (i = 0; i < 64; i++) {
      p[i] = component.blockData[blockBufferOffset + i] * qt[i];
    }

    // inverse DCT on rows
    for (i = 0; i < 8; ++i) {
      var row = 8 * i;

      // check for all-zero AC coefficients
      if (p[1 + row] == 0 && p[2 + row] == 0 && p[3 + row] == 0 &&
          p[4 + row] == 0 && p[5 + row] == 0 && p[6 + row] == 0 &&
          p[7 + row] == 0) {
        t = (dctSqrt2 * p[0 + row] + 512) >> 10;
        p[0 + row] = t;
        p[1 + row] = t;
        p[2 + row] = t;
        p[3 + row] = t;
        p[4 + row] = t;
        p[5 + row] = t;
        p[6 + row] = t;
        p[7 + row] = t;
        continue;
      }

      // stage 4
      v0 = (dctSqrt2 * p[0 + row] + 128) >> 8;
      v1 = (dctSqrt2 * p[4 + row] + 128) >> 8;
      v2 = p[2 + row];
      v3 = p[6 + row];
      v4 = (dctSqrt1d2 * (p[1 + row] - p[7 + row]) + 128) >> 8;
      v7 = (dctSqrt1d2 * (p[1 + row] + p[7 + row]) + 128) >> 8;
      v5 = p[3 + row] << 4;
      v6 = p[5 + row] << 4;

      // stage 3
      t = (v0 - v1+ 1) >> 1;
      v0 = (v0 + v1 + 1) >> 1;
      v1 = t;
      t = (v2 * dctSin6 + v3 * dctCos6 + 128) >> 8;
      v2 = (v2 * dctCos6 - v3 * dctSin6 + 128) >> 8;
      v3 = t;
      t = (v4 - v6 + 1) >> 1;
      v4 = (v4 + v6 + 1) >> 1;
      v6 = t;
      t = (v7 + v5 + 1) >> 1;
      v5 = (v7 - v5 + 1) >> 1;
      v7 = t;

      // stage 2
      t = (v0 - v3 + 1) >> 1;
      v0 = (v0 + v3 + 1) >> 1;
      v3 = t;
      t = (v1 - v2 + 1) >> 1;
      v1 = (v1 + v2 + 1) >> 1;
      v2 = t;
      t = (v4 * dctSin3 + v7 * dctCos3 + 2048) >> 12;
      v4 = (v4 * dctCos3 - v7 * dctSin3 + 2048) >> 12;
      v7 = t;
      t = (v5 * dctSin1 + v6 * dctCos1 + 2048) >> 12;
      v5 = (v5 * dctCos1 - v6 * dctSin1 + 2048) >> 12;
      v6 = t;

      // stage 1
      p[0 + row] = v0 + v7;
      p[7 + row] = v0 - v7;
      p[1 + row] = v1 + v6;
      p[6 + row] = v1 - v6;
      p[2 + row] = v2 + v5;
      p[5 + row] = v2 - v5;
      p[3 + row] = v3 + v4;
      p[4 + row] = v3 - v4;
    }

    // inverse DCT on columns
    for (i = 0; i < 8; ++i) {
      var col = i;

      // check for all-zero AC coefficients
      if (p[1*8 + col] == 0 && p[2*8 + col] == 0 && p[3*8 + col] == 0 &&
          p[4*8 + col] == 0 && p[5*8 + col] == 0 && p[6*8 + col] == 0 &&
          p[7*8 + col] == 0) {
        t = (dctSqrt2 * p[i+0] + 8192) >> 14;
        p[0*8 + col] = t;
        p[1*8 + col] = t;
        p[2*8 + col] = t;
        p[3*8 + col] = t;
        p[4*8 + col] = t;
        p[5*8 + col] = t;
        p[6*8 + col] = t;
        p[7*8 + col] = t;
        continue;
      }

      // stage 4
      v0 = (dctSqrt2 * p[0*8 + col] + 2048) >> 12;
      v1 = (dctSqrt2 * p[4*8 + col] + 2048) >> 12;
      v2 = p[2*8 + col];
      v3 = p[6*8 + col];
      v4 = (dctSqrt1d2 * (p[1*8 + col] - p[7*8 + col]) + 2048) >> 12;
      v7 = (dctSqrt1d2 * (p[1*8 + col] + p[7*8 + col]) + 2048) >> 12;
      v5 = p[3*8 + col];
      v6 = p[5*8 + col];

      // stage 3
      t = (v0 - v1 + 1) >> 1;
      v0 = (v0 + v1 + 1) >> 1;
      v1 = t;
      t = (v2 * dctSin6 + v3 * dctCos6 + 2048) >> 12;
      v2 = (v2 * dctCos6 - v3 * dctSin6 + 2048) >> 12;
      v3 = t;
      t = (v4 - v6 + 1) >> 1;
      v4 = (v4 + v6 + 1) >> 1;
      v6 = t;
      t = (v7 + v5 + 1) >> 1;
      v5 = (v7 - v5 + 1) >> 1;
      v7 = t;

      // stage 2
      t = (v0 - v3 + 1) >> 1;
      v0 = (v0 + v3 + 1) >> 1;
      v3 = t;
      t = (v1 - v2 + 1) >> 1;
      v1 = (v1 + v2 + 1) >> 1;
      v2 = t;
      t = (v4 * dctSin3 + v7 * dctCos3 + 2048) >> 12;
      v4 = (v4 * dctCos3 - v7 * dctSin3 + 2048) >> 12;
      v7 = t;
      t = (v5 * dctSin1 + v6 * dctCos1 + 2048) >> 12;
      v5 = (v5 * dctCos1 - v6 * dctSin1 + 2048) >> 12;
      v6 = t;

      // stage 1
      p[0*8 + col] = v0 + v7;
      p[7*8 + col] = v0 - v7;
      p[1*8 + col] = v1 + v6;
      p[6*8 + col] = v1 - v6;
      p[2*8 + col] = v2 + v5;
      p[5*8 + col] = v2 - v5;
      p[3*8 + col] = v3 + v4;
      p[4*8 + col] = v3 - v4;
    }

    // convert to 8-bit integers
    for (i = 0; i < 64; ++i) {
      var index = blockBufferOffset + i;
      var q = p[i];
      q = (q <= -2056) ? 0 : (q >= 2024) ? 255 : (q + 2056) >> 4;
      component.blockData[index] = q;
    }
  }

  function buildComponentData(frame, component) {
    var lines = [];
    var blocksPerLine = component.blocksPerLine;
    var blocksPerColumn = component.blocksPerColumn;
    var samplesPerLine = blocksPerLine << 3;
    var computationBuffer = new Int32Array(64);

    var i, j, ll = 0;
    for (var blockRow = 0; blockRow < blocksPerColumn; blockRow++) {
      for (var blockCol = 0; blockCol < blocksPerLine; blockCol++) {
        var offset = getBlockBufferOffset(component, blockRow, blockCol)
        quantizeAndInverse(component, offset, computationBuffer);
      }
    }
    return component.blockData;
  }

  function clampToUint8(a) {
    return a <= 0 ? 0 : a >= 255 ? 255 : a | 0;
  }

  constructor.prototype = {
    load: function load(path) {
      var handleData = (function(data) {
        this.parse(data);
        if (this.onload)
          this.onload();
      }).bind(this);

      if (path.indexOf("data:") > -1) {
        var offset = path.indexOf("base64,")+7;
        var data = atob(path.substring(offset));
        var arr = new Uint8Array(data.length);
        for (var i = data.length - 1; i >= 0; i--) {
          arr[i] = data.charCodeAt(i);
        }
        handleData(arr);
      } else {
        var xhr = new XMLHttpRequest();
        xhr.open("GET", path, true);
        xhr.responseType = "arraybuffer";
        xhr.onload = (function() {
          // TODO catch parse error
          var data = new Uint8Array(xhr.response);
          handleData(data);
        }).bind(this);
        xhr.send(null);
      }
    },

    parse: function parse(data) {

      function readUint16() {
        var value = (data[offset] << 8) | data[offset + 1];
        offset += 2;
        return value;
      }

      function readDataBlock() {
        var length = readUint16();
        var array = data.subarray(offset, offset + length - 2);
        offset += array.length;
        return array;
      }

      function prepareComponents(frame) {
        var mcusPerLine = Math.ceil(frame.samplesPerLine / 8 / frame.maxH);
        var mcusPerColumn = Math.ceil(frame.scanLines / 8 / frame.maxV);
        for (var i = 0; i < frame.components.length; i++) {
          component = frame.components[i];
          var blocksPerLine = Math.ceil(Math.ceil(frame.samplesPerLine / 8) * component.h / frame.maxH);
          var blocksPerColumn = Math.ceil(Math.ceil(frame.scanLines  / 8) * component.v / frame.maxV);
          var blocksPerLineForMcu = mcusPerLine * component.h;
          var blocksPerColumnForMcu = mcusPerColumn * component.v;

          var blocksBufferSize = 64 * blocksPerColumnForMcu
                                    * (blocksPerLineForMcu + 1);
          component.blockData = new Int16Array(blocksBufferSize);
          component.blocksPerLine = blocksPerLine;
          component.blocksPerColumn = blocksPerColumn;
        }
        frame.mcusPerLine = mcusPerLine;
        frame.mcusPerColumn = mcusPerColumn;
      }

      var offset = 0, length = data.length;
      var jfif = null;
      var adobe = null;
      var pixels = null;
      var frame, resetInterval;
      var quantizationTables = [];
      var huffmanTablesAC = [], huffmanTablesDC = [];
      var fileMarker = readUint16();
      if (fileMarker != 0xFFD8) { // SOI (Start of Image)
        throw "SOI not found";
      }

      fileMarker = readUint16();
      while (fileMarker != 0xFFD9) { // EOI (End of image)
        var i, j, l;
        switch(fileMarker) {
          case 0xFFE0: // APP0 (Application Specific)
          case 0xFFE1: // APP1
          case 0xFFE2: // APP2
          case 0xFFE3: // APP3
          case 0xFFE4: // APP4
          case 0xFFE5: // APP5
          case 0xFFE6: // APP6
          case 0xFFE7: // APP7
          case 0xFFE8: // APP8
          case 0xFFE9: // APP9
          case 0xFFEA: // APP10
          case 0xFFEB: // APP11
          case 0xFFEC: // APP12
          case 0xFFED: // APP13
          case 0xFFEE: // APP14
          case 0xFFEF: // APP15
          case 0xFFFE: // COM (Comment)
            var appData = readDataBlock();

            if (fileMarker === 0xFFE0) {
              if (appData[0] === 0x4A && appData[1] === 0x46 && appData[2] === 0x49 &&
                appData[3] === 0x46 && appData[4] === 0) { // 'JFIF\x00'
                jfif = {
                  version: { major: appData[5], minor: appData[6] },
                  densityUnits: appData[7],
                  xDensity: (appData[8] << 8) | appData[9],
                  yDensity: (appData[10] << 8) | appData[11],
                  thumbWidth: appData[12],
                  thumbHeight: appData[13],
                  thumbData: appData.subarray(14, 14 + 3 * appData[12] * appData[13])
                };
              }
            }
            // TODO APP1 - Exif
            if (fileMarker === 0xFFEE) {
              if (appData[0] === 0x41 && appData[1] === 0x64 && appData[2] === 0x6F &&
                appData[3] === 0x62 && appData[4] === 0x65 && appData[5] === 0) { // 'Adobe\x00'
                adobe = {
                  version: appData[6],
                  flags0: (appData[7] << 8) | appData[8],
                  flags1: (appData[9] << 8) | appData[10],
                  transformCode: appData[11]
                };
              }
            }
            break;

          case 0xFFDB: // DQT (Define Quantization Tables)
            var quantizationTablesLength = readUint16();
            var quantizationTablesEnd = quantizationTablesLength + offset - 2;
            while (offset < quantizationTablesEnd) {
              var quantizationTableSpec = data[offset++];
              var tableData = new Int32Array(64);
              if ((quantizationTableSpec >> 4) === 0) { // 8 bit values
                for (j = 0; j < 64; j++) {
                  var z = dctZigZag[j];
                  tableData[z] = data[offset++];
                }
              } else if ((quantizationTableSpec >> 4) === 1) { //16 bit
                for (j = 0; j < 64; j++) {
                  var z = dctZigZag[j];
                  tableData[z] = readUint16();
                }
              } else
                throw "DQT: invalid table spec";
              quantizationTables[quantizationTableSpec & 15] = tableData;
            }
            break;

          case 0xFFC0: // SOF0 (Start of Frame, Baseline DCT)
          case 0xFFC1: // SOF1 (Start of Frame, Extended DCT)
          case 0xFFC2: // SOF2 (Start of Frame, Progressive DCT)
            if (frame) {
              throw "Only single frame JPEGs supported";
            }
            readUint16(); // skip data length
            frame = {};
            frame.extended = (fileMarker === 0xFFC1);
            frame.progressive = (fileMarker === 0xFFC2);
            frame.precision = data[offset++];
            frame.scanLines = readUint16();
            frame.samplesPerLine = readUint16();
            frame.components = [];
            frame.componentIds = {};
            var componentsCount = data[offset++], componentId;
            var maxH = 0, maxV = 0;
            for (i = 0; i < componentsCount; i++) {
              componentId = data[offset];
              var h = data[offset + 1] >> 4;
              var v = data[offset + 1] & 15;
              if (maxH < h) maxH = h;
              if (maxV < v) maxV = v;
              var qId = data[offset + 2];
              var l = frame.components.push({
                h: h,
                v: v,
                quantizationTable: quantizationTables[qId]
              });
              frame.componentIds[componentId] = l - 1;
              offset += 3;
            }
            frame.maxH = maxH;
            frame.maxV = maxV;
            prepareComponents(frame);
            break;

          case 0xFFC4: // DHT (Define Huffman Tables)
            var huffmanLength = readUint16();
            for (i = 2; i < huffmanLength;) {
              var huffmanTableSpec = data[offset++];
              var codeLengths = new Uint8Array(16);
              var codeLengthSum = 0;
              for (j = 0; j < 16; j++, offset++)
                codeLengthSum += (codeLengths[j] = data[offset]);
              var huffmanValues = new Uint8Array(codeLengthSum);
              for (j = 0; j < codeLengthSum; j++, offset++)
                huffmanValues[j] = data[offset];
              i += 17 + codeLengthSum;

              ((huffmanTableSpec >> 4) === 0 ?
                huffmanTablesDC : huffmanTablesAC)[huffmanTableSpec & 15] =
                buildHuffmanTable(codeLengths, huffmanValues);
            }
            break;

          case 0xFFDD: // DRI (Define Restart Interval)
            readUint16(); // skip data length
            resetInterval = readUint16();
            break;

          case 0xFFDA: // SOS (Start of Scan)
            var scanLength = readUint16();
            var selectorsCount = data[offset++];
            var components = [], component;
            for (i = 0; i < selectorsCount; i++) {
              var componentIndex = frame.componentIds[data[offset++]];
              component = frame.components[componentIndex];
              var tableSpec = data[offset++];
              component.huffmanTableDC = huffmanTablesDC[tableSpec >> 4];
              component.huffmanTableAC = huffmanTablesAC[tableSpec & 15];
              components.push(component);
            }
            var spectralStart = data[offset++];
            var spectralEnd = data[offset++];
            var successiveApproximation = data[offset++];
            var processed = decodeScan(data, offset,
              frame, components, resetInterval,
              spectralStart, spectralEnd,
              successiveApproximation >> 4, successiveApproximation & 15);
            offset += processed;
            break;
          default:
            if (data[offset - 3] == 0xFF &&
                data[offset - 2] >= 0xC0 && data[offset - 2] <= 0xFE) {
              // could be incorrect encoding -- last 0xFF byte of the previous
              // block was eaten by the encoder
              offset -= 3;
              break;
            }
            throw "unknown JPEG marker " + fileMarker.toString(16);
        }
        fileMarker = readUint16();
      }

      this.width = frame.samplesPerLine;
      this.height = frame.scanLines;
      this.jfif = jfif;
      this.adobe = adobe;
      this.components = [];
      for (var i = 0; i < frame.components.length; i++) {
        var component = frame.components[i];
        this.components.push({
          output: buildComponentData(frame, component),
          scaleX: component.h / frame.maxH,
          scaleY: component.v / frame.maxV,
          blocksPerLine: component.blocksPerLine,
          blocksPerColumn: component.blocksPerColumn
        });
      }
    },

    getData: function getData(width, height) {
      var scaleX = this.width / width, scaleY = this.height / height;

      var component, componentScaleX, componentScaleY;
      var x, y, i;
      var offset = 0;
      var Y, Cb, Cr, K, C, M, Ye, R, G, B;
      var colorTransform;
      var numComponents = this.components.length;
      var dataLength = width * height * numComponents;
      var data = new Uint8Array(dataLength);
      var componentLine;

      // lineData is reused for all components. Assume first component is
      // the biggest
      var lineData = new Uint8Array((this.components[0].blocksPerLine << 3) *
                                    this.components[0].blocksPerColumn * 8);

      // First construct image data ...
      for (i = 0; i < numComponents; i++) {
        component = this.components[i];
        var blocksPerLine = component.blocksPerLine;
        var blocksPerColumn = component.blocksPerColumn;
        var samplesPerLine = blocksPerLine << 3;

        var j, k, ll = 0;
        var lineOffset = 0;
        for (var blockRow = 0; blockRow < blocksPerColumn; blockRow++) {
          var scanLine = blockRow << 3;
          for (var blockCol = 0; blockCol < blocksPerLine; blockCol++) {
            var bufferOffset = getBlockBufferOffset(component, blockRow, blockCol);
            var offset = 0, sample = blockCol << 3;
            for (j = 0; j < 8; j++) {
              var lineOffset = (scanLine + j) * samplesPerLine;
              for (k = 0; k < 8; k++) {
                lineData[lineOffset + sample + k] =
                  component.output[bufferOffset + offset++];
              }
            }
          }
        }

        componentScaleX = component.scaleX * scaleX;
        componentScaleY = component.scaleY * scaleY;
        offset = i;

        var cx, cy;
        var index;
        for (y = 0; y < height; y++) {
          for (x = 0; x < width; x++) {
            cy = 0 | (y * componentScaleY);
            cx = 0 | (x * componentScaleX);
            index = cy * samplesPerLine + cx;
            data[offset] = lineData[index];
            offset += numComponents;
          }
        }
      }

      // ... then transform colors, if necessary
      switch (numComponents) {
        case 1: case 2: break;
        // no color conversion for one or two compoenents

        case 3:
          // The default transform for three components is true
          colorTransform = true;
          // The adobe transform marker overrides any previous setting
          if (this.adobe && this.adobe.transformCode)
            colorTransform = true;
          else if (typeof this.colorTransform !== 'undefined')
            colorTransform = !!this.colorTransform;

          if (colorTransform) {
            for (i = 0; i < dataLength; i += numComponents) {
              Y  = data[i    ];
              Cb = data[i + 1];
              Cr = data[i + 2];

              R = clampToUint8(Y - 179.456 + 1.402 * Cr);
              G = clampToUint8(Y + 135.459 - 0.344 * Cb - 0.714 * Cr);
              B = clampToUint8(Y - 226.816 + 1.772 * Cb);

              data[i    ] = R;
              data[i + 1] = G;
              data[i + 2] = B;
            }
          }
          break;
        case 4:
          if (!this.adobe)
            throw 'Unsupported color mode (4 components)';
          // The default transform for four components is false
          colorTransform = false;
          // The adobe transform marker overrides any previous setting
          if (this.adobe && this.adobe.transformCode)
            colorTransform = true;
          else if (typeof this.colorTransform !== 'undefined')
            colorTransform = !!this.colorTransform;

          if (colorTransform) {
            for (i = 0; i < dataLength; i += numComponents) {
              Y  = data[i];
              Cb = data[i + 1];
              Cr = data[i + 2];

              C = clampToUint8(434.456 - Y - 1.402 * Cr);
              M = clampToUint8(119.541 - Y + 0.344 * Cb + 0.714 * Cr);
              Y = clampToUint8(481.816 - Y - 1.772 * Cb);

              data[i    ] = C;
              data[i + 1] = M;
              data[i + 2] = Y;
              // K is unchanged
            }
          }
          break;
        default:
          throw 'Unsupported color mode';
      }
      return data;
    },
    copyToImageData: function copyToImageData(imageData) {
      var width = imageData.width, height = imageData.height;
      var imageDataBytes = width * height * 4;
      var imageDataArray = imageData.data;
      var data = this.getData(width, height);
      var i = 0, j = 0, k0, k1;
      var Y, K, C, M, R, G, B;
      switch (this.components.length) {
        case 1:
          while (j < imageDataBytes) {
            Y = data[i++];

            imageDataArray[j++] = Y;
            imageDataArray[j++] = Y;
            imageDataArray[j++] = Y;
            imageDataArray[j++] = 255;
          }
          break;
        case 3:
          while (j < imageDataBytes) {
            R = data[i++];
            G = data[i++];
            B = data[i++];

            imageDataArray[j++] = R;
            imageDataArray[j++] = G;
            imageDataArray[j++] = B;
            imageDataArray[j++] = 255;
          }
          break;
        case 4:
          while (j < imageDataBytes) {
            C = data[i++];
            M = data[i++];
            Y = data[i++];
            K = data[i++];

            k0 = 255 - K;
            k1 = k0 / 255;


            R = clampToUint8(k0 - C * k1);
            G = clampToUint8(k0 - M * k1);
            B = clampToUint8(k0 - Y * k1);

            imageDataArray[j++] = R;
            imageDataArray[j++] = G;
            imageDataArray[j++] = B;
            imageDataArray[j++] = 255;
          }
          break;
        default:
          throw 'Unsupported color mode';
      }
    }
  };

  return constructor;
})();