text: 
  /* Copyright 2014 Mozilla Foundation
   *
   * 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.
   */
  
  /*
  This code was forked from https://github.com/notmasteryet/jpgjs. The original
  version was created by github user notmasteryet
  
  - 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)
  */
  
  'use strict';
  
  var JpegImage = (function jpegImage() {
    var dctZigZag = new Uint8Array([
       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;
        while (true) {
          node = node[readBit()];
          if (typeof node === 'number') {
            return node;
          }
          if (typeof node !== 'object') {
            throw 'invalid huffman sequence';
          }
        }
      }
  
      function receive(length) {
        var n = 0;
        while (length > 0) {
          n = (n << 1) | readBit();
          length--;
        }
        return n;
      }
  
      function receiveAndExtend(length) {
        if (length === 1) {
          return readBit() === 1 ? 1 : -1;
        }
        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;
        var e = spectralEnd;
        var r = 0;
        var s;
        var rs;
        while (k <= e) {
          var z = dctZigZag[k];
          switch (successiveACState) {
          case 0: // initial state
            rs = decodeHuffman(component.huffmanTableAC);
            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, blockData = component.blockData;
      var v0, v1, v2, v3, v4, v5, v6, v7;
      var p0, p1, p2, p3, p4, p5, p6, p7;
      var t;
  
      // inverse DCT on rows
      for (var row = 0; row < 64; row += 8) {
        // gather block data
        p0 = blockData[blockBufferOffset + row];
        p1 = blockData[blockBufferOffset + row + 1];
        p2 = blockData[blockBufferOffset + row + 2];
        p3 = blockData[blockBufferOffset + row + 3];
        p4 = blockData[blockBufferOffset + row + 4];
        p5 = blockData[blockBufferOffset + row + 5];
        p6 = blockData[blockBufferOffset + row + 6];
        p7 = blockData[blockBufferOffset + row + 7];
  
        // dequant p0
        p0 *= qt[row];
  
        // check for all-zero AC coefficients
        if ((p1 | p2 | p3 | p4 | p5 | p6 | p7) === 0) {
          t = (dctSqrt2 * p0 + 512) >> 10;
          p[row] = t;
          p[row + 1] = t;
          p[row + 2] = t;
          p[row + 3] = t;
          p[row + 4] = t;
          p[row + 5] = t;
          p[row + 6] = t;
          p[row + 7] = t;
          continue;
        }
        // dequant p1 ... p7
        p1 *= qt[row + 1];
        p2 *= qt[row + 2];
        p3 *= qt[row + 3];
        p4 *= qt[row + 4];
        p5 *= qt[row + 5];
        p6 *= qt[row + 6];
        p7 *= qt[row + 7];
  
        // stage 4
        v0 = (dctSqrt2 * p0 + 128) >> 8;
        v1 = (dctSqrt2 * p4 + 128) >> 8;
        v2 = p2;
        v3 = p6;
        v4 = (dctSqrt1d2 * (p1 - p7) + 128) >> 8;
        v7 = (dctSqrt1d2 * (p1 + p7) + 128) >> 8;
        v5 = p3 << 4;
        v6 = p5 << 4;
  
        // stage 3
        v0 = (v0 + v1 + 1) >> 1;
        v1 = v0 - v1;
        t  = (v2 * dctSin6 + v3 * dctCos6 + 128) >> 8;
        v2 = (v2 * dctCos6 - v3 * dctSin6 + 128) >> 8;
        v3 = t;
        v4 = (v4 + v6 + 1) >> 1;
        v6 = v4 - v6;
        v7 = (v7 + v5 + 1) >> 1;
        v5 = v7 - v5;
  
        // stage 2
        v0 = (v0 + v3 + 1) >> 1;
        v3 = v0 - v3;
        v1 = (v1 + v2 + 1) >> 1;
        v2 = v1 - v2;
        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[row] = v0 + v7;
        p[row + 7] = v0 - v7;
        p[row + 1] = v1 + v6;
        p[row + 6] = v1 - v6;
        p[row + 2] = v2 + v5;
        p[row + 5] = v2 - v5;
        p[row + 3] = v3 + v4;
        p[row + 4] = v3 - v4;
      }
  
      // inverse DCT on columns
      for (var col = 0; col < 8; ++col) {
        p0 = p[col];
        p1 = p[col +  8];
        p2 = p[col + 16];
        p3 = p[col + 24];
        p4 = p[col + 32];
        p5 = p[col + 40];
        p6 = p[col + 48];
        p7 = p[col + 56];
  
        // check for all-zero AC coefficients
        if ((p1 | p2 | p3 | p4 | p5 | p6 | p7) === 0) {
          t = (dctSqrt2 * p0 + 8192) >> 14;
          // convert to 8 bit
          t = (t < -2040) ? 0 : (t >= 2024) ? 255 : (t + 2056) >> 4;
          blockData[blockBufferOffset + col] = t;
          blockData[blockBufferOffset + col +  8] = t;
          blockData[blockBufferOffset + col + 16] = t;
          blockData[blockBufferOffset + col + 24] = t;
          blockData[blockBufferOffset + col + 32] = t;
          blockData[blockBufferOffset + col + 40] = t;
          blockData[blockBufferOffset + col + 48] = t;
          blockData[blockBufferOffset + col + 56] = t;
          continue;
        }
  
        // stage 4
        v0 = (dctSqrt2 * p0 + 2048) >> 12;
        v1 = (dctSqrt2 * p4 + 2048) >> 12;
        v2 = p2;
        v3 = p6;
        v4 = (dctSqrt1d2 * (p1 - p7) + 2048) >> 12;
        v7 = (dctSqrt1d2 * (p1 + p7) + 2048) >> 12;
        v5 = p3;
        v6 = p5;
  
        // stage 3
        // Shift v0 by 128.5 << 5 here, so we don't need to shift p0...p7 when
        // converting to UInt8 range later.
        v0 = ((v0 + v1 + 1) >> 1) + 4112;
        v1 = v0 - v1;
        t  = (v2 * dctSin6 + v3 * dctCos6 + 2048) >> 12;
        v2 = (v2 * dctCos6 - v3 * dctSin6 + 2048) >> 12;
        v3 = t;
        v4 = (v4 + v6 + 1) >> 1;
        v6 = v4 - v6;
        v7 = (v7 + v5 + 1) >> 1;
        v5 = v7 - v5;
  
        // stage 2
        v0 = (v0 + v3 + 1) >> 1;
        v3 = v0 - v3;
        v1 = (v1 + v2 + 1) >> 1;
        v2 = v1 - v2;
        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
        p0 = v0 + v7;
        p7 = v0 - v7;
        p1 = v1 + v6;
        p6 = v1 - v6;
        p2 = v2 + v5;
        p5 = v2 - v5;
        p3 = v3 + v4;
        p4 = v3 - v4;
  
        // convert to 8-bit integers
        p0 = (p0 < 16) ? 0 : (p0 >= 4080) ? 255 : p0 >> 4;
        p1 = (p1 < 16) ? 0 : (p1 >= 4080) ? 255 : p1 >> 4;
        p2 = (p2 < 16) ? 0 : (p2 >= 4080) ? 255 : p2 >> 4;
        p3 = (p3 < 16) ? 0 : (p3 >= 4080) ? 255 : p3 >> 4;
        p4 = (p4 < 16) ? 0 : (p4 >= 4080) ? 255 : p4 >> 4;
        p5 = (p5 < 16) ? 0 : (p5 >= 4080) ? 255 : p5 >> 4;
        p6 = (p6 < 16) ? 0 : (p6 >= 4080) ? 255 : p6 >> 4;
        p7 = (p7 < 16) ? 0 : (p7 >= 4080) ? 255 : p7 >> 4;
  
        // store block data
        blockData[blockBufferOffset + col] = p0;
        blockData[blockBufferOffset + col +  8] = p1;
        blockData[blockBufferOffset + col + 16] = p2;
        blockData[blockBufferOffset + col + 24] = p3;
        blockData[blockBufferOffset + col + 32] = p4;
        blockData[blockBufferOffset + col + 40] = p5;
        blockData[blockBufferOffset + col + 48] = p6;
        blockData[blockBufferOffset + col + 56] = p7;
      }
    }
  
    function buildComponentData(frame, component) {
      var blocksPerLine = component.blocksPerLine;
      var blocksPerColumn = component.blocksPerColumn;
      var computationBuffer = new Int16Array(64);
  
      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 clamp0to255(a) {
      return a <= 0 ? 0 : a >= 255 ? 255 : a;
    }
  
    constructor.prototype = {
      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) { // 'Adobe'
                  adobe = {
                    version: (appData[5] << 8) | 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;
              var z;
              while (offset < quantizationTablesEnd) {
                var quantizationTableSpec = data[offset++];
                var tableData = new Uint16Array(64);
                if ((quantizationTableSpec >> 4) === 0) { // 8 bit values
                  for (j = 0; j < 64; j++) {
                    z = dctZigZag[j];
                    tableData[z] = data[offset++];
                  }
                } else if ((quantizationTableSpec >> 4) === 1) { //16 bit
                  for (j = 0; j < 64; j++) {
                    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];
                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;
  
            case 0xFFFF: // Fill bytes
              if (data[offset] !== 0xFF) { // Avoid skipping a valid marker.
                offset--;
              }
              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 (i = 0; i < frame.components.length; i++) {
          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
          });
        }
        this.numComponents = this.components.length;
      },
  
      _getLinearizedBlockData: function getLinearizedBlockData(width, height) {
        var scaleX = this.width / width, scaleY = this.height / height;
  
        var component, componentScaleX, componentScaleY, blocksPerScanline;
        var x, y, i, j, k;
        var index;
        var offset = 0;
        var output;
        var numComponents = this.components.length;
        var dataLength = width * height * numComponents;
        var data = new Uint8Array(dataLength);
        var xScaleBlockOffset = new Uint32Array(width);
        var mask3LSB = 0xfffffff8; // used to clear the 3 LSBs
  
        for (i = 0; i < numComponents; i++) {
          component = this.components[i];
          componentScaleX = component.scaleX * scaleX;
          componentScaleY = component.scaleY * scaleY;
          offset = i;
          output = component.output;
          blocksPerScanline = (component.blocksPerLine + 1) << 3;
          // precalculate the xScaleBlockOffset
          for (x = 0; x < width; x++) {
            j = 0 | (x * componentScaleX);
            xScaleBlockOffset[x] = ((j & mask3LSB) << 3) | (j & 7);
          }
          // linearize the blocks of the component
          for (y = 0; y < height; y++) {
            j = 0 | (y * componentScaleY);
            index = blocksPerScanline * (j & mask3LSB) | ((j & 7) << 3);
            for (x = 0; x < width; x++) {
              data[offset] = output[index + xScaleBlockOffset[x]];
              offset += numComponents;
            }
          }
        }
  
        // decodeTransform contains pairs of multiplier (-256..256) and additive
        var transform = this.decodeTransform;
        if (transform) {
          for (i = 0; i < dataLength;) {
            for (j = 0, k = 0; j < numComponents; j++, i++, k += 2) {
              data[i] = ((data[i] * transform[k]) >> 8) + transform[k + 1];
            }
          }
        }
        return data;
      },
  
      _isColorConversionNeeded: function isColorConversionNeeded() {
        if (this.adobe && this.adobe.transformCode) {
          // The adobe transform marker overrides any previous setting
          return true;
        } else if (this.numComponents === 3) {
          return true;
        } else {
          return false;
        }
      },
  
      _convertYccToRgb: function convertYccToRgb(data) {
        var Y, Cb, Cr;
        for (var i = 0, length = data.length; i < length; i += 3) {
          Y  = data[i    ];
          Cb = data[i + 1];
          Cr = data[i + 2];
          data[i    ] = clamp0to255(Y - 179.456 + 1.402 * Cr);
          data[i + 1] = clamp0to255(Y + 135.459 - 0.344 * Cb - 0.714 * Cr);
          data[i + 2] = clamp0to255(Y - 226.816 + 1.772 * Cb);
        }
        return data;
      },
  
      _convertYcckToRgb: function convertYcckToRgb(data) {
        var Y, Cb, Cr, k;
        var offset = 0;
        for (var i = 0, length = data.length; i < length; i += 4) {
          Y  = data[i];
          Cb = data[i + 1];
          Cr = data[i + 2];
          k = data[i + 3];
  
          var r = -122.67195406894 +
            Cb * (-6.60635669420364e-5 * Cb + 0.000437130475926232 * Cr -
                  5.4080610064599e-5 * Y + 0.00048449797120281 * k -
                  0.154362151871126) +
            Cr * (-0.000957964378445773 * Cr + 0.000817076911346625 * Y -
                  0.00477271405408747 * k + 1.53380253221734) +
            Y * (0.000961250184130688 * Y - 0.00266257332283933 * k +
                 0.48357088451265) +
            k * (-0.000336197177618394 * k + 0.484791561490776);
  
          var g = 107.268039397724 +
            Cb * (2.19927104525741e-5 * Cb - 0.000640992018297945 * Cr +
                  0.000659397001245577 * Y + 0.000426105652938837 * k -
                  0.176491792462875) +
            Cr * (-0.000778269941513683 * Cr + 0.00130872261408275 * Y +
                  0.000770482631801132 * k - 0.151051492775562) +
            Y * (0.00126935368114843 * Y - 0.00265090189010898 * k +
                 0.25802910206845) +
            k * (-0.000318913117588328 * k - 0.213742400323665);
  
          var b = -20.810012546947 +
            Cb * (-0.000570115196973677 * Cb - 2.63409051004589e-5 * Cr +
                  0.0020741088115012 * Y - 0.00288260236853442 * k +
                  0.814272968359295) +
            Cr * (-1.53496057440975e-5 * Cr - 0.000132689043961446 * Y +
                  0.000560833691242812 * k - 0.195152027534049) +
            Y * (0.00174418132927582 * Y - 0.00255243321439347 * k +
                 0.116935020465145) +
            k * (-0.000343531996510555 * k + 0.24165260232407);
  
          data[offset++] = clamp0to255(r);
          data[offset++] = clamp0to255(g);
          data[offset++] = clamp0to255(b);
        }
        return data;
      },
  
      _convertYcckToCmyk: function convertYcckToCmyk(data) {
        var Y, Cb, Cr;
        for (var i = 0, length = data.length; i < length; i += 4) {
          Y  = data[i];
          Cb = data[i + 1];
          Cr = data[i + 2];
          data[i    ] = clamp0to255(434.456 - Y - 1.402 * Cr);
          data[i + 1] = clamp0to255(119.541 - Y + 0.344 * Cb + 0.714 * Cr);
          data[i + 2] = clamp0to255(481.816 - Y - 1.772 * Cb);
          // K in data[i + 3] is unchanged
        }
        return data;
      },
  
      _convertCmykToRgb: function convertCmykToRgb(data) {
        var c, m, y, k;
        var offset = 0;
        var min = -255 * 255 * 255;
        var scale = 1 / 255 / 255;
        for (var i = 0, length = data.length; i < length; i += 4) {
          c = data[i];
          m = data[i + 1];
          y = data[i + 2];
          k = data[i + 3];
  
          var r =
            c * (-4.387332384609988 * c + 54.48615194189176 * m +
                 18.82290502165302 * y + 212.25662451639585 * k -
                 72734.4411664936) +
            m * (1.7149763477362134 * m - 5.6096736904047315 * y -
                 17.873870861415444 * k - 1401.7366389350734) +
            y * (-2.5217340131683033 * y - 21.248923337353073 * k +
                 4465.541406466231) -
            k * (21.86122147463605 * k + 48317.86113160301);
          var g =
            c * (8.841041422036149 * c + 60.118027045597366 * m +
                 6.871425592049007 * y + 31.159100130055922 * k -
                 20220.756542821975) +
            m * (-15.310361306967817 * m + 17.575251261109482 * y +
                 131.35250912493976 * k - 48691.05921601825) +
            y * (4.444339102852739 * y + 9.8632861493405 * k -
                 6341.191035517494) -
            k * (20.737325471181034 * k + 47890.15695978492);
          var b =
            c * (0.8842522430003296 * c + 8.078677503112928 * m +
                 30.89978309703729 * y - 0.23883238689178934 * k -
                 3616.812083916688) +
            m * (10.49593273432072 * m + 63.02378494754052 * y +
                 50.606957656360734 * k - 28620.90484698408) +
            y * (0.03296041114873217 * y + 115.60384449646641 * k -
                 49363.43385999684) -
            k * (22.33816807309886 * k + 45932.16563550634);
  
          data[offset++] = r >= 0 ? 255 : r <= min ? 0 : 255 + r * scale | 0;
          data[offset++] = g >= 0 ? 255 : g <= min ? 0 : 255 + g * scale | 0;
          data[offset++] = b >= 0 ? 255 : b <= min ? 0 : 255 + b * scale | 0;
        }
        return data;
      },
  
      getData: function getData(width, height, forceRGBoutput) {
        if (this.numComponents > 4) {
          throw 'Unsupported color mode';
        }
        // type of data: Uint8Array(width * height * numComponents)
        var data = this._getLinearizedBlockData(width, height);
  
        if (this.numComponents === 3) {
          return this._convertYccToRgb(data);
        } else if (this.numComponents === 4) {
          if (this._isColorConversionNeeded()) {
            if (forceRGBoutput) {
              return this._convertYcckToRgb(data);
            } else {
              return this._convertYcckToCmyk(data);
            }
          } else if (forceRGBoutput) {
            return this._convertCmykToRgb(data);
          }
        }
        return data;
      }
    };
  
    return constructor;
  })();
  