text: /**
   * tng.js - png reader
   * Copyright (c) 2015, Christopher Jeffrey (MIT License).
   * https://github.com/chjj/tng
   */
  
  var fs = require('fs')
    , util = require('util')
    , path = require('path')
    , zlib = require('zlib')
    , assert = require('assert')
    , cp = require('child_process')
    , exec = cp.execFileSync;
  
  /**
   * PNG
   */
  
  function PNG(file, options) {
    var buf
      , chunks
      , idat
      , pixels;
  
    if (!(this instanceof PNG)) {
      return new PNG(file, options);
    }
  
    if (!file) throw new Error('no file');
  
    this.options = options || {};
    this.colors = options.colors || require('blessed/lib/colors');
    this.optimization = this.options.optimization || 'mem';
    this.speed = this.options.speed || 1;
  
    if (Buffer.isBuffer(file)) {
      this.file = this.options.filename || null;
      buf = file;
    } else {
      this.options.filename = file;
      this.file = path.resolve(process.cwd(), file);
      buf = fs.readFileSync(this.file);
    }
  
    this.format = buf.readUInt32BE(0) === 0x89504e47 ? 'png'
      : buf.slice(0, 3).toString('ascii') === 'GIF' ? 'gif'
      : buf.readUInt16BE(0) === 0xffd8 ? 'jpg'
      : path.extname(this.file).slice(1).toLowerCase() || 'png';
  
    if (this.format !== 'png') {
      try {
        return this.toPNG(buf);
      } catch (e) {
        throw e;
      }
    }
  
    chunks = this.parseRaw(buf);
    idat = this.parseChunks(chunks);
    pixels = this.parseLines(idat);
  
    this.bmp = this.createBitmap(pixels);
    this.cellmap = this.createCellmap(this.bmp);
    this.frames = this.compileFrames(this.frames);
  }
  
  PNG.prototype.parseRaw = function(buf) {
    var chunks = []
      , index = 0
      , i = 0
      , buf
      , len
      , type
      , name
      , data
      , crc
      , check
      , critical
      , public_
      , conforming
      , copysafe
      , pos;
  
    this._debug(this.file);
  
    if (buf.readUInt32BE(0) !== 0x89504e47
        || buf.readUInt32BE(4) !== 0x0d0a1a0a) {
      throw new Error('bad header');
    }
  
    i += 8;
  
    while (i < buf.length) {
      try {
        len = buf.readUInt32BE(i);
        i += 4;
        pos = i;
        type = buf.slice(i, i + 4);
        name = type.toString('ascii');
        i += 4;
        data = buf.slice(i, i + len);
        i += len;
        check = this.crc32(buf.slice(pos, i));
        crc = buf.readInt32BE(i);
        i += 4;
        critical = !!(~type[0] & 32);
        public_ = !!(~type[1] & 32);
        conforming = !!(~type[2] & 32);
        copysafe = !!(~type[3] & 32);
        if (crc !== check) {
          throw new Error(name + ': bad crc');
        }
      } catch (e) {
        if (this.options.debug) throw e;
        break;
      }
      chunks.push({
        index: index++,
        id: name.toLowerCase(),
        len: len,
        pos: pos,
        end: i,
        type: type,
        name: name,
        data: data,
        crc: crc,
        check: check,
        raw: buf.slice(pos, i),
        flags: {
          critical: critical,
          public_: public_,
          conforming: conforming,
          copysafe: copysafe
        }
      });
    }
  
    return chunks;
  };
  
  PNG.prototype.parseChunks = function(chunks) {
    var i
      , chunk
      , name
      , data
      , p
      , idat
      , info;
  
    for (i = 0; i < chunks.length; i++) {
      chunk = chunks[i];
      name = chunk.id;
      data = chunk.data;
      info = {};
      switch (name) {
        case 'ihdr': {
          this.width = info.width = data.readUInt32BE(0);
          this.height = info.height = data.readUInt32BE(4);
          this.bitDepth = info.bitDepth = data.readUInt8(8);
          this.colorType = info.colorType = data.readUInt8(9);
          this.compression = info.compression = data.readUInt8(10);
          this.filter = info.filter = data.readUInt8(11);
          this.interlace = info.interlace = data.readUInt8(12);
          switch (this.bitDepth) {
            case 1: case 2: case 4: case 8: case 16: case 24: case 32: break;
            default: throw new Error('bad bit depth: ' + this.bitDepth);
          }
          switch (this.colorType) {
            case 0: case 2: case 3: case 4: case 6: break;
            default: throw new Error('bad color: ' + this.colorType);
          }
          switch (this.compression) {
            case 0: break;
            default: throw new Error('bad compression: ' + this.compression);
          }
          switch (this.filter) {
            case 0: case 1: case 2: case 3: case 4: break;
            default: throw new Error('bad filter: ' + this.filter);
          }
          switch (this.interlace) {
            case 0: case 1: break;
            default: throw new Error('bad interlace: ' + this.interlace);
          }
          break;
        }
        case 'plte': {
          this.palette = info.palette = [];
          for (p = 0; p < data.length; p += 3) {
            this.palette.push({
              r: data[p + 0],
              g: data[p + 1],
              b: data[p + 2],
              a: 255
            });
          }
          break;
        }
        case 'idat': {
          this.size = this.size || 0;
          this.size += data.length;
          this.idat = this.idat || [];
          this.idat.push(data);
          info.size = data.length;
          break;
        }
        case 'iend': {
          this.end = true;
          break;
        }
        case 'trns': {
          this.alpha = info.alpha = Array.prototype.slice.call(data);
          if (this.palette) {
            for (p = 0; p < data.length; p++) {
              if (!this.palette[p]) break;
              this.palette[p].a = data[p];
            }
          }
          break;
        }
        // https://wiki.mozilla.org/APNG_Specification
        case 'actl': {
          this.actl = info = {};
          this.frames = [];
          this.actl.numFrames = data.readUInt32BE(0);
          this.actl.numPlays = data.readUInt32BE(4);
          break;
        }
        case 'fctl': {
          // IDAT is the first frame depending on the order:
          // IDAT is a frame: acTL->fcTL->IDAT->[fcTL]->fdAT
          // IDAT is not a frame: acTL->IDAT->[fcTL]->fdAT
          if (!this.idat) {
            this.idat = [];
            this.frames.push({
              idat: true,
              fctl: info,
              fdat: this.idat
            });
          } else {
            this.frames.push({
              fctl: info,
              fdat: []
            });
          }
          info.sequenceNumber = data.readUInt32BE(0);
          info.width = data.readUInt32BE(4);
          info.height = data.readUInt32BE(8);
          info.xOffset = data.readUInt32BE(12);
          info.yOffset = data.readUInt32BE(16);
          info.delayNum = data.readUInt16BE(20);
          info.delayDen = data.readUInt16BE(22);
          info.disposeOp = data.readUInt8(24);
          info.blendOp = data.readUInt8(25);
          break;
        }
        case 'fdat': {
          info.sequenceNumber = data.readUInt32BE(0);
          info.data = data.slice(4);
          this.frames[this.frames.length - 1].fdat.push(info.data);
          break;
        }
      }
      chunk.info = info;
    }
  
    this._debug(chunks);
  
    if (this.frames) {
      this.frames = this.frames.map(function(frame, i) {
        frame.fdat = this.decompress(frame.fdat);
        if (!frame.fdat.length) throw new Error('no data');
        return frame;
      }, this);
    }
  
    idat = this.decompress(this.idat);
    if (!idat.length) throw new Error('no data');
  
    return idat;
  };
  
  PNG.prototype.parseLines = function(data) {
    var pixels = []
      , x
      , p
      , prior
      , line
      , filter
      , samples
      , pendingSamples
      , ch
      , shiftStart
      , i
      , toShift
      , sample;
  
    this.sampleDepth =
      this.colorType === 0 ? 1
      : this.colorType === 2 ? 3
      : this.colorType === 3 ? 1
      : this.colorType === 4 ? 2
      : this.colorType === 6 ? 4
      : 1;
    this.bitsPerPixel = this.bitDepth * this.sampleDepth;
    this.bytesPerPixel = Math.ceil(this.bitsPerPixel / 8);
    this.wastedBits = ((this.width * this.bitsPerPixel) / 8) - ((this.width * this.bitsPerPixel / 8) | 0);
    this.byteWidth = Math.ceil(this.width * (this.bitsPerPixel / 8));
  
    this.shiftStart = ((this.bitDepth + (8 / this.bitDepth - this.bitDepth)) - 1) | 0;
    this.shiftMult = this.bitDepth >= 8 ? 0 : this.bitDepth;
    this.mask = this.bitDepth === 32 ? 0xffffffff : (1 << this.bitDepth) - 1;
  
    if (this.interlace === 1) {
      samples = this.sampleInterlacedLines(data);
      for (i = 0; i < samples.length; i += this.sampleDepth) {
        pixels.push(samples.slice(i, i + this.sampleDepth));
      }
      return pixels;
    }
  
    for (p = 0; p < data.length; p += this.byteWidth) {
      prior = line || [];
      filter = data[p++];
      line = data.slice(p, p + this.byteWidth);
      line = this.unfilterLine(filter, line, prior);
      samples = this.sampleLine(line);
      for (i = 0; i < samples.length; i += this.sampleDepth) {
        pixels.push(samples.slice(i, i + this.sampleDepth));
      }
    }
  
    return pixels;
  };
  
  PNG.prototype.unfilterLine = function(filter, line, prior) {
    for (var x = 0; x < line.length; x++) {
      if (filter === 0) {
        break;
      } else if (filter === 1) {
        line[x] = this.filters.sub(x, line, prior, this.bytesPerPixel);
      } else if (filter === 2) {
        line[x] = this.filters.up(x, line, prior, this.bytesPerPixel);
      } else if (filter === 3) {
        line[x] = this.filters.average(x, line, prior, this.bytesPerPixel);
      } else if (filter === 4) {
        line[x] = this.filters.paeth(x, line, prior, this.bytesPerPixel);
      }
    }
    return line;
  };
  
  PNG.prototype.sampleLine = function(line, width) {
    var samples = []
      , x = 0
      , pendingSamples
      , ch
      , i
      , sample
      , shiftStart
      , toShift;
  
    while (x < line.length) {
      pendingSamples = this.sampleDepth;
      while (pendingSamples--) {
        ch = line[x];
        if (this.bitDepth === 16) {
          ch = (ch << 8) | line[++x];
        } else if (this.bitDepth === 24) {
          ch = (ch << 16) | (line[++x] << 8) | line[++x];
        } else if (this.bitDepth === 32) {
          ch = (ch << 24) | (line[++x] << 16) | (line[++x] << 8) | line[++x];
        } else if (this.bitDepth > 32) {
          throw new Error('bitDepth ' + this.bitDepth + ' unsupported.');
        }
        shiftStart = this.shiftStart;
        toShift = shiftStart - (x === line.length - 1 ? this.wastedBits : 0);
        for (i = 0; i <= toShift; i++) {
          sample = (ch >> (this.shiftMult * shiftStart)) & this.mask;
          if (this.colorType !== 3) {
            if (this.bitDepth < 8) { // <= 8 would work too, doesn't matter
              // sample = sample * (0xff / this.mask) | 0; // would work too
              sample *= 0xff / this.mask;
              sample |= 0;
            } else if (this.bitDepth > 8) {
              sample = (sample / this.mask) * 255 | 0;
            }
          }
          samples.push(sample);
          shiftStart--;
        }
        x++;
      }
    }
  
    // Needed for deinterlacing?
    if (width != null) {
      samples = samples.slice(0, width * this.sampleDepth);
    }
  
    return samples;
  };
  
  // http://www.w3.org/TR/PNG-Filters.html
  PNG.prototype.filters = {
    sub: function Sub(x, line, prior, bpp) {
      if (x < bpp) return line[x];
      return (line[x] + line[x - bpp]) % 256;
    },
    up: function Up(x, line, prior, bpp) {
      return (line[x] + (prior[x] || 0)) % 256;
    },
    average: function Average(x, line, prior, bpp) {
      if (x < bpp) return Math.floor((prior[x] || 0) / 2);
      // if (x < bpp) return (prior[x] || 0) >> 1;
      return (line[x]
        + Math.floor((line[x - bpp] + prior[x]) / 2)
        // + ((line[x - bpp] + prior[x]) >> 1)
      ) % 256;
    },
    paeth: function Paeth(x, line, prior, bpp) {
      if (x < bpp) return prior[x] || 0;
      return (line[x] + this._predictor(
        line[x - bpp], prior[x] || 0, prior[x - bpp] || 0
      )) % 256;
    },
    _predictor: function PaethPredictor(a, b, c) {
      // a = left, b = above, c = upper left
      var p = a + b - c
        , pa = Math.abs(p - a)
        , pb = Math.abs(p - b)
        , pc = Math.abs(p - c);
      if (pa <= pb && pa <= pc) return a;
      if (pb <= pc) return b;
      return c;
    }
  };
  
  /**
   * Adam7 deinterlacing ported to javascript from PyPNG:
   * pypng - Pure Python library for PNG image encoding/decoding
   * Copyright (c) 2009-2015, David Jones (MIT License).
   * https://github.com/drj11/pypng
   *
   * Permission is hereby granted, free of charge, to any person
   * obtaining a copy of this software and associated documentation files
   * (the "Software"), to deal in the Software without restriction,
   * including without limitation the rights to use, copy, modify, merge,
   * publish, distribute, sublicense, and/or sell copies of the Software,
   * and to permit persons to whom the Software is furnished to do so,
   * subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be
   * included in all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
   * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
   * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
   * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
   * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
   * SOFTWARE.
   */
  
  PNG.prototype.sampleInterlacedLines = function(raw) {
    var psize
      , vpr
      , samples
      , source_offset
      , i
      , pass
      , xstart
      , ystart
      , xstep
      , ystep
      , recon
      , ppr
      , row_size
      , y
      , filter_type
      , scanline
      , flat
      , offset
      , k
      , end_offset
      , skip
      , j
      , k
      , f;
  
    var adam7 = [
      [0, 0, 8, 8],
      [4, 0, 8, 8],
      [0, 4, 4, 8],
      [2, 0, 4, 4],
      [0, 2, 2, 4],
      [1, 0, 2, 2],
      [0, 1, 1, 2]
    ];
  
    // Fractional bytes per pixel
    psize = (this.bitDepth / 8) * this.sampleDepth;
  
    // Values per row (of the target image)
    vpr = this.width * this.sampleDepth;
  
    // Make a result array, and make it big enough. Interleaving
    // writes to the output array randomly (well, not quite), so the
    // entire output array must be in memory.
    samples = new Buffer(vpr * this.height);
    samples.fill(0);
  
    source_offset = 0;
  
    for (i = 0; i < adam7.length; i++) {
      pass = adam7[i];
      xstart = pass[0];
      ystart = pass[1];
      xstep = pass[2];
      ystep = pass[3];
      if (xstart >= this.width) continue;
      // The previous (reconstructed) scanline. Empty array at the
      // beginning of a pass to indicate that there is no previous
      // line.
      recon = [];
      // Pixels per row (reduced pass image)
      ppr = Math.ceil((this.width - xstart) / xstep);
      // Row size in bytes for this pass.
      row_size = Math.ceil(psize * ppr);
      for (y = ystart; y < this.height; y += ystep) {
        filter_type = raw[source_offset];
        source_offset += 1;
        scanline = raw.slice(source_offset, source_offset + row_size);
        source_offset += row_size;
        recon = this.unfilterLine(filter_type, scanline, recon);
        // Convert so that there is one element per pixel value
        flat = this.sampleLine(recon, ppr);
        if (xstep === 1) {
          assert.equal(xstart, 0);
          offset = y * vpr;
          for (k = offset, f = 0; k < offset + vpr; k++, f++) {
            samples[k] = flat[f];
          }
        } else {
          offset = y * vpr + xstart * this.sampleDepth;
          end_offset = (y + 1) * vpr;
          skip = this.sampleDepth * xstep;
          for (j = 0; j < this.sampleDepth; j++) {
            for (k = offset + j, f = j; k < end_offset; k += skip, f += this.sampleDepth) {
              samples[k] = flat[f];
            }
          }
        }
      }
    }
  
    return samples;
  };
  
  PNG.prototype.createBitmap = function(pixels) {
    var bmp = []
      , i;
  
    if (this.colorType === 0) {
      pixels = pixels.map(function(sample) {
        return { r: sample[0], g: sample[0], b: sample[0], a: 255 };
      });
    } else if (this.colorType === 2) {
      pixels = pixels.map(function(sample) {
        return { r: sample[0], g: sample[1], b: sample[2], a: 255 };
      });
    } else if (this.colorType === 3) {
      pixels = pixels.map(function(sample) {
        if (!this.palette[sample[0]]) throw new Error('bad palette index');
        return this.palette[sample[0]];
      }, this);
    } else if (this.colorType === 4) {
      pixels = pixels.map(function(sample) {
        return { r: sample[0], g: sample[0], b: sample[0], a: sample[1] };
      });
    } else if (this.colorType === 6) {
      pixels = pixels.map(function(sample) {
        return { r: sample[0], g: sample[1], b: sample[2], a: sample[3] };
      });
    }
  
    for (i = 0; i < pixels.length; i += this.width) {
      bmp.push(pixels.slice(i, i + this.width));
    }
  
    return bmp;
  };
  
  PNG.prototype.createCellmap = function(bmp, options) {
    var bmp = bmp || this.bmp
      , options = options || this.options
      , cellmap = []
      , scale = options.scale || 0.20
      , height = bmp.length
      , width = bmp[0].length
      , cmwidth = options.width
      , cmheight = options.height
      , line
      , x
      , y
      , xx
      , yy
      , scale
      , xs
      , ys;
  
    if (cmwidth) {
      scale = cmwidth / width;
    } else if (cmheight) {
      scale = cmheight / height;
    }
  
    if (!cmheight) {
      cmheight = Math.round(height * scale);
    }
  
    if (!cmwidth) {
      cmwidth = Math.round(width * scale);
    }
  
    ys = height / cmheight;
    xs = width / cmwidth;
  
    for (y = 0; y < bmp.length; y += ys) {
      line = [];
      yy = Math.round(y);
      if (!bmp[yy]) break;
      for (x = 0; x < bmp[yy].length; x += xs) {
        xx = Math.round(x);
        if (!bmp[yy][xx]) break;
        line.push(bmp[yy][xx]);
      }
      cellmap.push(line);
    }
  
    return cellmap;
  };
  
  PNG.prototype.renderANSI = function(bmp) {
    var self = this
      , out = '';
  
    bmp.forEach(function(line, y) {
      line.forEach(function(pixel, x) {
        var outch = self.getOutch(x, y, line, pixel);
        out += self.pixelToSGR(pixel, outch);
      });
      out += '\n';
    });
  
    return out;
  };
  
  PNG.prototype.renderContent = function(bmp, el) {
    var self = this
      , out = '';
  
    bmp.forEach(function(line, y) {
      line.forEach(function(pixel, x) {
        var outch = self.getOutch(x, y, line, pixel);
        out += self.pixelToTags(pixel, outch);
      });
      out += '\n';
    });
  
    el.setContent(out);
  
    return out;
  };
  
  PNG.prototype.renderScreen = function(bmp, screen, xi, xl, yi, yl) {
    var self = this
      , lines = screen.lines
      , cellLines
      , y
      , yy
      , x
      , xx
      , alpha
      , attr
      , ch;
  
    cellLines = bmp.reduce(function(cellLines, line, y) {
      var cellLine = [];
      line.forEach(function(pixel, x) {
        var outch = self.getOutch(x, y, line, pixel)
          , cell = self.pixelToCell(pixel, outch);
        cellLine.push(cell);
      });
      cellLines.push(cellLine);
      return cellLines;
    }, []);
  
    for (y = yi; y < yl; y++) {
      yy = y - yi;
      for (x = xi; x < xl; x++) {
        xx = x - xi;
        if (lines[y] && lines[y][x] && cellLines[yy] && cellLines[yy][xx]) {
          alpha = cellLines[yy][xx].pop();
          // completely transparent
          if (alpha === 0.0) {
            continue;
          }
          // translucency / blending
          if (alpha < 1.0) {
            attr = cellLines[yy][xx][0];
            ch = cellLines[yy][xx][1];
            lines[y][x][0] = this.colors.blend(lines[y][x][0], attr, alpha);
            if (ch !== ' ') lines[y][x][1] = ch;
            lines[y].dirty = true;
            continue;
          }
          // completely opaque
          lines[y][x] = cellLines[yy][xx];
          lines[y].dirty = true;
        }
      }
    }
  };
  
  PNG.prototype.renderElement = function(bmp, el) {
    var xi = el.aleft + el.ileft
      , xl = el.aleft + el.width - el.iright
      , yi = el.atop + el.itop
      , yl = el.atop + el.height - el.ibottom;
  
    return this.renderScreen(bmp, el.screen, xi, xl, yi, yl);
  };
  
  PNG.prototype.pixelToSGR = function(pixel, ch) {
    var bga = 1.0
      , fga = 0.5
      , a = pixel.a / 255
      , bg
      , fg;
  
    bg = this.colors.match(
      pixel.r * a * bga | 0,
      pixel.g * a * bga | 0,
      pixel.b * a * bga | 0);
  
    if (ch && this.options.ascii) {
      fg = this.colors.match(
        pixel.r * a * fga | 0,
        pixel.g * a * fga | 0,
        pixel.b * a * fga | 0);
      if (a === 0) {
        return '\x1b[38;5;' + fg + 'm' + ch + '\x1b[m';
      }
      return '\x1b[38;5;' + fg + 'm\x1b[48;5;' + bg + 'm' + ch + '\x1b[m';
    }
  
    if (a === 0) return ' ';
  
    return '\x1b[48;5;' + bg + 'm \x1b[m';
  };
  
  PNG.prototype.pixelToTags = function(pixel, ch) {
    var bga = 1.0
      , fga = 0.5
      , a = pixel.a / 255
      , bg
      , fg;
  
    bg = this.colors.RGBtoHex(
      pixel.r * a * bga | 0,
      pixel.g * a * bga | 0,
      pixel.b * a * bga | 0);
  
    if (ch && this.options.ascii) {
      fg = this.colors.RGBtoHex(
        pixel.r * a * fga | 0,
        pixel.g * a * fga | 0,
        pixel.b * a * fga | 0);
      if (a === 0) {
        return '{' + fg + '-fg}' + ch + '{/}';
      }
      return '{' + fg + '-fg}{' + bg + '-bg}' + ch + '{/}';
    }
  
    if (a === 0) return ' ';
  
    return '{' + bg + '-bg} {/' + bg + '-bg}';
  };
  
  PNG.prototype.pixelToCell = function(pixel, ch) {
    var bga = 1.0
      , fga = 0.5
      , a = pixel.a / 255
      , bg
      , fg;
  
    bg = this.colors.match(
      pixel.r * bga | 0,
      pixel.g * bga | 0,
      pixel.b * bga | 0);
  
    if (ch && this.options.ascii) {
      fg = this.colors.match(
        pixel.r * fga | 0,
        pixel.g * fga | 0,
        pixel.b * fga | 0);
    } else {
      fg = 0x1ff;
      ch = null;
    }
  
    // if (a === 0) bg = 0x1ff;
  
    return [(0 << 18) | (fg << 9) | (bg << 0), ch || ' ', a];
  };
  
  // Taken from libcaca:
  PNG.prototype.getOutch = (function() {
    var dchars = '????8@8@#8@8##8#MKXWwz$&%x><\\/xo;+=|^-:i\'.`,  `.        ';
  
    var luminance = function(pixel) {
      var a = pixel.a / 255
        , r = pixel.r * a
        , g = pixel.g * a
        , b = pixel.b * a
        , l = 0.2126 * r + 0.7152 * g + 0.0722 * b;
  
      return l / 255;
    };
  
    return function(x, y, line, pixel) {
      var lumi = luminance(pixel)
        , outch = dchars[lumi * (dchars.length - 1) | 0];
  
      return outch;
    };
  })();
  
  PNG.prototype.compileFrames = function(frames) {
    return this.optimization === 'mem'
      ? this.compileFrames_lomem(frames)
      : this.compileFrames_locpu(frames);
  };
  
  PNG.prototype.compileFrames_lomem = function(frames) {
    if (!this.actl) return;
    return frames.map(function(frame, i) {
      this.width = frame.fctl.width;
      this.height = frame.fctl.height;
  
      var pixels = frame._pixels || this.parseLines(frame.fdat)
        , bmp = frame._bmp || this.createBitmap(pixels)
        , fc = frame.fctl;
  
      return {
        actl: this.actl,
        fctl: frame.fctl,
        delay: (fc.delayNum / (fc.delayDen || 100)) * 1000 | 0,
        bmp: bmp
      };
    }, this);
  };
  
  PNG.prototype.compileFrames_locpu = function(frames) {
    if (!this.actl) return;
  
    this._curBmp = null;
    this._lastBmp = null;
  
    return frames.map(function(frame, i) {
      this.width = frame.fctl.width;
      this.height = frame.fctl.height;
  
      var pixels = frame._pixels || this.parseLines(frame.fdat)
        , bmp = frame._bmp || this.createBitmap(pixels)
        , renderBmp = this.renderFrame(bmp, frame, i)
        , cellmap = this.createCellmap(renderBmp)
        , fc = frame.fctl;
  
      return {
        actl: this.actl,
        fctl: frame.fctl,
        delay: (fc.delayNum / (fc.delayDen || 100)) * 1000 | 0,
        bmp: renderBmp,
        cellmap: cellmap
      };
    }, this);
  };
  
  PNG.prototype.renderFrame = function(bmp, frame, i) {
    var first = this.frames[0]
      , last = this.frames[i - 1]
      , fc = frame.fctl
      , xo = fc.xOffset
      , yo = fc.yOffset
      , lxo
      , lyo
      , x
      , y
      , line
      , p;
  
    if (!this._curBmp) {
      this._curBmp = [];
      for (y = 0; y < first.fctl.height; y++) {
        line = [];
        for (x = 0; x < first.fctl.width; x++) {
          p = bmp[y][x];
          line.push({ r: p.r, g: p.g, b: p.b, a: p.a });
        }
        this._curBmp.push(line);
      }
    }
  
    if (last && last.fctl.disposeOp !== 0) {
      lxo = last.fctl.xOffset;
      lyo = last.fctl.yOffset;
      for (y = 0; y < last.fctl.height; y++) {
        for (x = 0; x < last.fctl.width; x++) {
          if (last.fctl.disposeOp === 0) {
            // none / keep
          } else if (last.fctl.disposeOp === 1) {
            // background / clear
            this._curBmp[lyo + y][lxo + x] = { r: 0, g: 0, b: 0, a: 0 };
          } else if (last.fctl.disposeOp === 2) {
            // previous / restore
            p = this._lastBmp[y][x];
            this._curBmp[lyo + y][lxo + x] = { r: p.r, g: p.g, b: p.b, a: p.a };
          }
        }
      }
    }
  
    if (frame.fctl.disposeOp === 2) {
      this._lastBmp = [];
      for (y = 0; y < frame.fctl.height; y++) {
        line = [];
        for (x = 0; x < frame.fctl.width; x++) {
          p = this._curBmp[yo + y][xo + x];
          line.push({ r: p.r, g: p.g, b: p.b, a: p.a });
        }
        this._lastBmp.push(line);
      }
    } else {
      this._lastBmp = null;
    }
  
    for (y = 0; y < frame.fctl.height; y++) {
      for (x = 0; x < frame.fctl.width; x++) {
        p = bmp[y][x];
        if (fc.blendOp === 0) {
          // source
          this._curBmp[yo + y][xo + x] = { r: p.r, g: p.g, b: p.b, a: p.a };
        } else if (fc.blendOp === 1) {
          // over
          if (p.a !== 0) {
            this._curBmp[yo + y][xo + x] = { r: p.r, g: p.g, b: p.b, a: p.a };
          }
        }
      }
    }
  
    return this._curBmp;
  };
  
  PNG.prototype._animate = function(callback) {
    if (!this.frames) {
      return callback(this.bmp, this.cellmap);
    }
  
    var self = this
      , numPlays = this.actl.numPlays || Infinity
      , running = 0
      , i = -1;
  
    this._curBmp = null;
    this._lastBmp = null;
  
    var next_lomem = function() {
      if (!running) return;
  
      var frame = self.frames[++i];
      if (!frame) {
        if (!--numPlays) return callback();
        i = -1;
        // XXX may be able to optimize by only setting the self._curBmp once???
        self._curBmp = null;
        self._lastBmp = null;
        return setImmediate(next);
      }
  
      var bmp = frame.bmp
        , renderBmp = self.renderFrame(bmp, frame, i)
        , cellmap = self.createCellmap(renderBmp);
  
      callback(renderBmp, cellmap);
      return setTimeout(next, frame.delay / self.speed | 0);
    };
  
    var next_locpu = function() {
      if (!running) return;
      var frame = self.frames[++i];
      if (!frame) {
        if (!--numPlays) return callback();
        i = -1;
        return setImmediate(next);
      }
      callback(frame.bmp, frame.cellmap);
      return setTimeout(next, frame.delay / self.speed | 0);
    };
  
    var next = this.optimization === 'mem'
      ? next_lomem
      : next_locpu;
  
    this._control = function(state) {
      if (state === -1) {
        i = -1;
        self._curBmp = null;
        self._lastBmp = null;
        running = 0;
        callback(self.frames[0].bmp,
          self.frames[0].cellmap || self.createCellmap(self.frames[0].bmp));
        return;
      }
      if (state === running) return;
      running = state;
      return next();
    };
  
    this._control(1);
  };
  
  PNG.prototype.play = function(callback) {
    if (!this._control || callback) {
      this.stop();
      return this._animate(callback);
    }
    this._control(1);
  };
  
  PNG.prototype.pause = function() {
    if (!this._control) return;
    this._control(0);
  };
  
  PNG.prototype.stop = function() {
    if (!this._control) return;
    this._control(-1);
  };
  
  PNG.prototype.toPNG = function(input) {
    var options = this.options
      , file = this.file
      , format = this.format
      , buf
      , img
      , gif
      , i
      , control
      , disposeOp;
  
    if (format !== 'gif') {
      buf = exec('convert', [format + ':-', 'png:-'],
        { stdio: ['pipe', 'pipe', 'ignore'], input: input });
      img = PNG(buf, options);
      img.file = file;
      return img;
    }
  
    gif = GIF(input, options);
  
    this.width = gif.width;
    this.height = gif.height;
    this.frames = [];
  
    for (i = 0; i < gif.images.length; i++) {
      img = gif.images[i];
      // Convert from gif disposal to png disposal. See:
      // http://www.w3.org/Graphics/GIF/spec-gif89a.txt
      control = img.control || gif;
      disposeOp = Math.max(0, (control.disposeMethod || 0) - 1);
      if (disposeOp > 2) disposeOp = 0;
      this.frames.push({
        fctl: {
          sequenceNumber: i,
          width: img.width,
          height: img.height,
          xOffset: img.left,
          yOffset: img.top,
          delayNum: control.delay,
          delayDen: 100,
          disposeOp: disposeOp,
          blendOp: 1
        },
        fdat: [],
        _pixels: [],
        _bmp: img.bmp
      });
    }
  
    this.bmp = this.frames[0]._bmp;
    this.cellmap = this.createCellmap(this.bmp);
  
    if (this.frames.length > 1) {
      this.actl = { numFrames: gif.images.length, numPlays: gif.numPlays || 0 };
      this.frames = this.compileFrames(this.frames);
    } else {
      this.frames = undefined;
    }
  
    return this;
  };
  
  // Convert a gif to an apng using imagemagick. Unfortunately imagemagick
  // doesn't support apngs, so we coalesce the gif frames into one image and then
  // slice them into frames.
  PNG.prototype.gifMagick = function(input) {
    var options = this.options
      , file = this.file
      , format = this.format
      , buf
      , fmt
      , img
      , frames
      , frame
      , width
      , height
      , iwidth
      , twidth
      , i
      , lines
      , line
      , x
      , y;
  
    buf = exec('convert',
      [format + ':-', '-coalesce', '+append', 'png:-'],
      { stdio: ['pipe', 'pipe', 'ignore'], input: input });
  
    fmt = '{"W":%W,"H":%H,"w":%w,"h":%h,"d":%T,"x":"%X","y":"%Y"},'
    frames = exec('identify', ['-format', fmt, format + ':-'],
      { encoding: 'utf8', stdio: ['pipe', 'pipe', 'ignore'], input: input });
    frames = JSON.parse('[' + frames.trim().slice(0, -1) + ']');
  
    img = PNG(buf, options);
    img.file = file;
    Object.keys(img).forEach(function(key) {
      this[key] = img[key];
    }, this);
  
    width = frames[0].W;
    height = frames[0].H;
    iwidth = 0;
    twidth = 0;
  
    this.width = width;
    this.height = height;
  
    this.frames = [];
  
    for (i = 0; i < frames.length; i++) {
      frame = frames[i];
      frame.x = +frame.x;
      frame.y = +frame.y;
  
      iwidth = twidth;
      twidth += width;
  
      lines = [];
      for (y = frame.y; y < height; y++) {
        line = [];
        for (x = iwidth + frame.x; x < twidth; x++) {
          line.push(img.bmp[y][x]);
        }
        lines.push(line);
      }
  
      this.frames.push({
        fctl: {
          sequenceNumber: i,
          width: frame.w,
          height: frame.h,
          xOffset: frame.x,
          yOffset: frame.y,
          delayNum: frame.d,
          delayDen: 100,
          disposeOp: 0,
          blendOp: 0
        },
        fdat: [],
        _pixels: [],
        _bmp: lines
      });
    }
  
    this.bmp = this.frames[0]._bmp;
    this.cellmap = this.createCellmap(this.bmp);
  
    if (this.frames.length > 1) {
      this.actl = { numFrames: frames.length, numPlays: 0 };
      this.frames = this.compileFrames(this.frames);
    } else {
      this.frames = undefined;
    }
  
    return this;
  };
  
  PNG.prototype.decompress = function(buffers) {
    return zlib.inflateSync(new Buffer(buffers.reduce(function(out, data) {
      return out.concat(Array.prototype.slice.call(data));
    }, [])));
  };
  
  /**
   * node-crc
   * https://github.com/alexgorbatchev/node-crc
   * https://github.com/alexgorbatchev/node-crc/blob/master/LICENSE
   *
   * The MIT License (MIT)
   *
   * Copyright 2014 Alex Gorbatchev
   *
   * Permission is hereby granted, free of charge, to any person obtaining
   * a copy of this software and associated documentation files (the
   * "Software"), to deal in the Software without restriction, including
   * without limitation the rights to use, copy, modify, merge, publish,
   * distribute, sublicense, and/or sell copies of the Software, and to
   * permit persons to whom the Software is furnished to do so, subject to
   * the following conditions:
   *
   * The above copyright notice and this permission notice shall be
   * included in all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
   * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
   * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
   * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
   * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
   * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
  
  PNG.prototype.crc32 = (function() {
    var crcTable = [
      0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
      0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
      0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
      0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
      0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
      0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
      0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
      0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
      0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
      0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
      0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
      0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
      0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
      0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
      0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
      0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
      0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
      0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
      0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
      0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
      0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
      0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
      0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
      0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
      0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
      0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
      0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
      0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
      0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
      0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
      0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
      0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
      0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
      0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
      0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
      0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
      0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
      0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
      0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
      0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
      0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
      0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
      0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
    ];
  
    return function crc32(buf) {
      //var crc = previous === 0 ? 0 : ~~previous ^ -1;
      var crc = -1;
      for (var i = 0, len = buf.length; i < len; i++) {
        crc = crcTable[(crc ^ buf[i]) & 0xff] ^ (crc >>> 8);
      }
      return crc ^ -1;
    };
  })();
  
  PNG.prototype._debug = function(obj) {
    if (!this.options.log) return;
    return this.options.log(util.inspect(obj, {
      depth: 20
    }));
  };
  
  /**
   * GIF
   */
  
  function GIF(file, options) {
    var self = this;
  
    if (!(this instanceof GIF)) {
      return new GIF(file, options);
    }
  
    var info = {}
      , p = 0
      , buf
      , i
      , total
      , sig
      , desc
      , img
      , ext
      , label
      , size;
  
    if (!file) throw new Error('no file');
  
    options = options || {};
  
    this.options = options;
  
    // XXX If the gif is not optimized enough
    // it may OOM the process with too many frames.
    // TODO: Implement in PNG reader.
    this.pixelLimit = this.options.pixelLimit || 7622550;
    this.totalPixels = 0;
  
    if (Buffer.isBuffer(file)) {
      buf = file;
      file = null;
    } else {
      file = path.resolve(process.cwd(), file);
      buf = fs.readFileSync(file);
    }
  
    sig = buf.slice(0, 6).toString('ascii');
    if (sig !== 'GIF87a' && sig !== 'GIF89a') {
      throw new Error('bad header: ' + sig);
    }
  
    this.width = buf.readUInt16LE(6);
    this.height = buf.readUInt16LE(8);
  
    this.flags = buf.readUInt8(10);
    this.gct = !!(this.flags & 0x80);
    this.gctsize = (this.flags & 0x07) + 1;
  
    this.bgIndex = buf.readUInt8(11);
    this.aspect = buf.readUInt8(12);
    p += 13;
  
    if (this.gct) {
      this.colors = [];
      total = 1 << this.gctsize;
      for (i = 0; i < total; i++, p += 3) {
        this.colors.push([buf[p], buf[p + 1], buf[p + 2], 255]);
      }
    }
  
    this.images = [];
    this.extensions = [];
  
    try {
      while (p < buf.length) {
        desc = buf.readUInt8(p);
        p += 1;
        if (desc === 0x2c) {
          img = {};
  
          img.left = buf.readUInt16LE(p);
          p += 2;
          img.top = buf.readUInt16LE(p);
          p += 2;
  
          img.width = buf.readUInt16LE(p);
          p += 2;
          img.height = buf.readUInt16LE(p);
          p += 2;
  
          img.flags = buf.readUInt8(p);
          p += 1;
  
          img.lct = !!(img.flags & 0x80);
          img.ilace = !!(img.flags & 0x40);
          img.lctsize = (img.flags & 0x07) + 1;
  
          if (img.lct) {
            img.lcolors = [];
            total = 1 << img.lctsize;
            for (i = 0; i < total; i++, p += 3) {
              img.lcolors.push([buf[p], buf[p + 1], buf[p + 2], 255]);
            }
          }
  
          img.codeSize = buf.readUInt8(p);
          p += 1;
  
          img.size = buf.readUInt8(p);
          p += 1;
  
          img.lzw = [buf.slice(p, p + img.size)];
          p += img.size;
  
          while (buf[p] !== 0x00) {
            // Some gifs screw up their size.
            // XXX Same for all subblocks?
            if (buf[p] === 0x3b && p === buf.length - 1) {
              p--;
              break;
            }
            size = buf.readUInt8(p);
            p += 1;
            img.lzw.push(buf.slice(p, p + size));
            p += size;
          }
  
          assert.equal(buf.readUInt8(p), 0x00);
          p += 1;
  
          if (ext && ext.label === 0xf9) {
            img.control = ext;
          }
  
          this.totalPixels += img.width * img.height;
  
          this.images.push(img);
  
          if (this.totalPixels >= this.pixelLimit) {
            break;
          }
        } else if (desc === 0x21) {
          // Extensions:
          // http://www.w3.org/Graphics/GIF/spec-gif89a.txt
          ext = {};
          label = buf.readUInt8(p);
          p += 1;
          ext.label = label;
          if (label === 0xf9) {
            size = buf.readUInt8(p);
            assert.equal(size, 0x04);
            p += 1;
            ext.fields = buf.readUInt8(p);
            ext.disposeMethod = (ext.fields >> 2) & 0x07;
            ext.useTransparent = !!(ext.fields & 0x01);
            p += 1;
            ext.delay = buf.readUInt16LE(p);
            p += 2;
            ext.transparentColor = buf.readUInt8(p);
            p += 1;
            while (buf[p] !== 0x00) {
              size = buf.readUInt8(p);
              p += 1;
              p += size;
            }
            assert.equal(buf.readUInt8(p), 0x00);
            p += 1;
            this.delay = ext.delay;
            this.transparentColor = ext.transparentColor;
            this.disposeMethod = ext.disposeMethod;
            this.useTransparent = ext.useTransparent;
          } else if (label === 0xff) {
            // https://wiki.whatwg.org/wiki/GIF#Specifications
            size = buf.readUInt8(p);
            p += 1;
            ext.id = buf.slice(p, p + 8).toString('ascii');
            p += 8;
            ext.auth = buf.slice(p, p + 3).toString('ascii');
            p += 3;
            ext.data = [];
            while (buf[p] !== 0x00) {
              size = buf.readUInt8(p);
              p += 1;
              ext.data.push(buf.slice(p, p + size));
              p += size;
            }
            ext.data = new Buffer(ext.data.reduce(function(out, data) {
              return out.concat(Array.prototype.slice.call(data));
            }, []));
            // AnimExts looping extension (identical to netscape)
            if (ext.id === 'ANIMEXTS' && ext.auth === '1.0') {
              ext.id = 'NETSCAPE';
              ext.auth = '2.0';
              ext.animexts = true;
            }
            // Netscape extensions
            if (ext.id === 'NETSCAPE' && ext.auth === '2.0') {
              if (ext.data.readUInt8(0) === 0x01) {
                // Netscape looping extension
                // http://graphcomp.com/info/specs/ani_gif.html
                ext.numPlays = ext.data.readUInt16LE(1);
                this.numPlays = ext.numPlays;
              } else if (ext.data.readUInt8(0) === 0x02) {
                // Netscape buffering extension
                this.minBuffer = ext.data;
              }
            }
            // Adobe XMP extension
            if (ext.id === 'XMP Data' && ext.auth === 'XMP') {
              ext.xmp = ext.data.toString('utf8');
              this.xmp = ext.xmp;
            }
            // ICC extension
            if (ext.id === 'ICCRGBG1' && ext.auth === '012') {
              // NOTE: Says size is 4 bytes, not 1? Maybe just buffer size?
              this.icc = ext.data;
            }
            // fractint extension
            if (ext.id === 'fractint' && /^00[1-7]$/.test(ext.auth)) {
              // NOTE: Says size is 4 bytes, not 1? Maybe just buffer size?
              // Size: '!\377\013' == [0x00, 0x15, 0xff, 0x0b]
              this.fractint = ext.data;
            }
            assert.equal(buf.readUInt8(p), 0x00);
            p += 1;
          } else {
            ext.data = [];
            while (buf[p] !== 0x00) {
              size = buf.readUInt8(p);
              p += 1;
              ext.data.push(buf.slice(p, p + size));
              p += size;
            }
            assert.equal(buf.readUInt8(p), 0x00);
            p += 1;
          }
          this.extensions.push(ext);
        } else if (desc === 0x3b) {
          break;
        } else if (p === buf.length - 1) {
          // } else if (desc === 0x00 && p === buf.length - 1) {
          break;
        } else {
          throw new Error('unknown block');
        }
      }
    } catch (e) {
      if (options.debug) {
        throw e;
      }
    }
  
    this.images = this.images.map(function(img, imageIndex) {
      var control = img.control || this;
  
      img.lzw = new Buffer(img.lzw.reduce(function(out, data) {
        return out.concat(Array.prototype.slice.call(data));
      }, []));
  
      try {
        img.data = this.decompress(img.lzw, img.codeSize);
      } catch (e) {
        if (options.debug) throw e;
        return;
      }
  
      var interlacing = [
        [ 0, 8 ],
        [ 4, 8 ],
        [ 2, 4 ],
        [ 1, 2 ],
        [ 0, 0 ]
      ];
  
      var table = img.lcolors || this.colors
        , row = 0
        , col = 0
        , ilp = 0
        , p = 0
        , b
        , idx
        , i
        , y
        , x
        , line
        , pixel;
  
      img.samples = [];
      // Rewritten version of:
      // https://github.com/lbv/ka-cs-programs/blob/master/lib/gif-reader.js
      for (;;) {
        b = img.data[p++];
        if (b == null) break;
        idx = (row * img.width + col) * 4;
        if (!table[b]) {
          if (options.debug) throw new Error('bad samples');
          table[b] = [0, 0, 0, 0];
        }
        img.samples[idx] = table[b][0];
        img.samples[idx + 1] = table[b][1];
        img.samples[idx + 2] = table[b][2];
        img.samples[idx + 3] = table[b][3];
        if (control.useTransparent && b === control.transparentColor) {
          img.samples[idx + 3] = 0;
        }
        if (++col >= img.width) {
          col = 0;
          if (img.ilace) {
            row += interlacing[ilp][1];
            if (row >= img.height) {
              row = interlacing[++ilp][0];
            }
          } else {
            row++;
          }
        }
      }
  
      img.pixels = [];
      for (i = 0; i < img.samples.length; i += 4) {
        img.pixels.push(img.samples.slice(i, i + 4));
      }
  
      img.bmp = [];
      for (y = 0, p = 0; y < img.height; y++) {
        line = [];
        for (x = 0; x < img.width; x++) {
          pixel = img.pixels[p++];
          if (!pixel) {
            if (options.debug) throw new Error('no pixel');
            line.push({ r: 0, g: 0, b: 0, a: 0 });
            continue;
          }
          line.push({ r: pixel[0], g: pixel[1], b: pixel[2], a: pixel[3] });
        }
        img.bmp.push(line);
      }
  
      return img;
    }, this).filter(Boolean);
  
    if (!this.images.length) {
      throw new Error('no image data or bad decompress');
    }
  }
  
  // Rewritten version of:
  // https://github.com/lbv/ka-cs-programs/blob/master/lib/gif-reader.js
  GIF.prototype.decompress = function(input, codeSize) {
    var bitDepth = codeSize + 1
      , CC = 1 << codeSize
      , EOI = CC + 1
      , stack = []
      , table = []
      , ntable = 0
      , oldCode = null
      , buffer = 0
      , nbuffer = 0
      , p = 0
      , buf = []
      , bits
      , read
      , ans
      , n
      , code
      , i
      , K
      , b
      , maxElem;
  
    for (;;) {
      if (stack.length === 0) {
        bits = bitDepth;
        read = 0;
        ans = 0;
        while (read < bits) {
          if (nbuffer === 0) {
            if (p >= input.length) return buf;
            buffer = input[p++];
            nbuffer = 8;
          }
          n = Math.min(bits - read, nbuffer);
          ans |= (buffer & ((1 << n) - 1)) << read;
          read += n;
          nbuffer -= n;
          buffer >>= n;
        }
        code = ans;
  
        if (code === EOI) {
          break;
        }
  
        if (code === CC) {
          table = [];
          for (i = 0; i < CC; ++i) {
            table[i] = [i, -1, i];
          }
          bitDepth = codeSize + 1;
          maxElem = 1 << bitDepth;
          ntable = CC + 2;
          oldCode = null;
          continue;
        }
  
        if (oldCode === null) {
          oldCode = code;
          buf.push(table[code][0]);
          continue;
        }
  
        if (code < ntable) {
          for (i = code; i >= 0; i = table[i][1]) {
            stack.push(table[i][0]);
          }
          table[ntable++] = [
            table[code][2],
            oldCode,
            table[oldCode][2]
          ];
        } else {
          K = table[oldCode][2];
          table[ntable++] = [K, oldCode, K];
          for (i = code; i >= 0; i = table[i][1]) {
            stack.push(table[i][0]);
          }
        }
  
        oldCode = code;
        if (ntable === maxElem) {
          maxElem = 1 << (++bitDepth);
          if (bitDepth > 12) bitDepth = 12;
        }
      }
      b = stack.pop();
      if (b == null) break;
      buf.push(b);
    }
  
    return buf;
  };
  
  /**
   * Expose
   */
  
  exports = PNG;
  exports.png = PNG;
  exports.gif = GIF;
  
  module.exports = exports;
  