pdf.js/src/core/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 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 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) {
      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;
    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 blocksPerLine = component.blocksPerLine;
    var blocksPerColumn = component.blocksPerColumn;
    var computationBuffer = new Int32Array(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 && 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;
            var z;
            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++) {
                  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;
          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 will 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, CbCb, CbCr, CbY, Cbk, CrCr, Crk, CrY, YY, Yk, kk;
      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];

        CbCb = Cb * Cb;
        CbCr = Cb * Cr;
        CbY = Cb * Y;
        Cbk = Cb * k;
        CrCr = Cr * Cr;
        Crk = Cr * k;
        CrY = Cr * Y;
        YY = Y * Y;
        Yk = Y * k;
        kk = k * k;

        var r = - 122.67195406894 -
          6.60635669420364e-5 * CbCb + 0.000437130475926232 * CbCr -
          5.4080610064599e-5* CbY + 0.00048449797120281* Cbk -
          0.154362151871126 * Cb - 0.000957964378445773 * CrCr +
          0.000817076911346625 * CrY - 0.00477271405408747 * Crk +
          1.53380253221734 * Cr + 0.000961250184130688 * YY -
          0.00266257332283933 * Yk + 0.48357088451265 * Y -
          0.000336197177618394 * kk + 0.484791561490776 * k;

        var g = 107.268039397724 +
          2.19927104525741e-5 * CbCb - 0.000640992018297945 * CbCr +
          0.000659397001245577* CbY + 0.000426105652938837* Cbk -
          0.176491792462875 * Cb - 0.000778269941513683 * CrCr +
          0.00130872261408275 * CrY + 0.000770482631801132 * Crk -
          0.151051492775562 * Cr + 0.00126935368114843 * YY -
          0.00265090189010898 * Yk + 0.25802910206845 * Y -
          0.000318913117588328 * kk - 0.213742400323665 * k;

        var b = - 20.810012546947 -
          0.000570115196973677 * CbCb - 2.63409051004589e-5 * CbCr +
          0.0020741088115012* CbY - 0.00288260236853442* Cbk +
          0.814272968359295 * Cb - 1.53496057440975e-5 * CrCr -
          0.000132689043961446 * CrY + 0.000560833691242812 * Crk -
          0.195152027534049 * Cr + 0.00174418132927582 * YY -
          0.00255243321439347 * Yk + 0.116935020465145 * Y -
          0.000343531996510555 * kk + 0.24165260232407 * k;

        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;
})();