Vue2.0实现调用摄像头进行拍照功能以及图片上传功能引用exif.js

可以在github 上下载demo链接 

https://github.com/fongdaBoy/Vue2.0ComponentDemo

vue组件代码

<template>
  <div>
    <div style="padding:20px;">
      <div class="show">
        <div class="picture" :style="'backgroundImage:url('+headerImage+')'">div>
      div>
      <div style="margin-top:20px;">
        <input type="file" id="upload" accept="image/jpg" @change="upload">
        <label for="upload">label>
      div>
    div>
  div>
template>

<script>
import {Exif} from './exif.js'

export default {
  data () {
    return {
      headerImage:'',picValue:''
    }
  },
  mounted () {
  },
  methods: {
    upload (e) {
      let files = e.target.files || e.dataTransfer.files;
      if (!files.length) return;
      this.picValue = files[0];
      this.imgPreview(this.picValue);
      console.log(this.picValue)
    },
    imgPreview (file) {
      let self = this;
      let Orientation;
      //去获取拍照时的信息，解决拍出来的照片旋转问题
       Exif.getData(file, function(){
           Orientation = Exif.getTag(this, 'Orientation');
       });
      // 看支持不支持FileReader  
      if (!file || !window.FileReader) return;

      if (/^image/.test(file.type)) {
          // 创建一个reader
          let reader = new FileReader();
          // 将图片2将转成 base64 格式
          reader.readAsDataURL(file);
          // 读取成功后的回调
          reader.onloadend = function () {
            let result = this.result;
            let img = new Image();
            img.src = result;
            //判断图片是否大于100K,是就直接上传，反之压缩图片
            if (this.result.length <= (100 * 1024)) {
              self.headerImage = this.result;
              self.postImg();
            }else {
              img.onload = function () {
                let data = self.compress(img,Orientation);
                self.headerImage = data;
                self.postImg();
              }
            }
          }
        }
      },
      postImg () {
        //这里写接口
      },
      rotateImg (img, direction,canvas) {
        //最小与最大旋转方向，图片旋转4次后回到原方向
        const min_step = 0;
        const max_step = 3;
        if (img == null)return;
        //img的高度和宽度不能在img元素隐藏后获取，否则会出错
        let height = img.height;
        let width = img.width;
        let step = 2;
        if (step == null) {
            step = min_step;
        }
        if (direction == 'right') {
            step++;
            //旋转到原位置，即超过最大值
            step > max_step && (step = min_step);
        } else {
            step--;
            step < min_step && (step = max_step);
        }
        //旋转角度以弧度值为参数
        let degree = step * 90 * Math.PI / 180;
        let ctx = canvas.getContext('2d');
        switch (step) {
          case 0:
              canvas.width = width;
              canvas.height = height;
              ctx.drawImage(img, 0, 0);
              break;
          case 1:
              canvas.width = height;
              canvas.height = width;
              ctx.rotate(degree);
              ctx.drawImage(img, 0, -height);
              break;
          case 2:
              canvas.width = width;
              canvas.height = height;
              ctx.rotate(degree);
              ctx.drawImage(img, -width, -height);
              break;
          case 3:
              canvas.width = height;
              canvas.height = width;
              ctx.rotate(degree);
              ctx.drawImage(img, -width, 0);
              break;
        }
    },
    compress(img,Orientation) {
      let canvas = document.createElement("canvas");
      let ctx = canvas.getContext('2d');
        //瓦片canvas
      let tCanvas = document.createElement("canvas");
      let tctx = tCanvas.getContext("2d");
      let initSize = img.src.length;
      let width = img.width;
      let height = img.height;
      //如果图片大于四百万像素，计算压缩比并将大小压至400万以下
      let ratio;
      if ((ratio = width * height / 4000000) > 1) {
        console.log("大于400万像素")
        ratio = Math.sqrt(ratio);
        width /= ratio;
        height /= ratio;
      } else {
        ratio = 1;
      }
      canvas.width = width;
      canvas.height = height;
  //        铺底色
      ctx.fillStyle = "#fff";
      ctx.fillRect(0, 0, canvas.width, canvas.height);
      //如果图片像素大于100万则使用瓦片绘制
      let count;
      if ((count = width * height / 1000000) > 1) {
        console.log("超过100W像素");
        count = ~~(Math.sqrt(count) + 1); //计算要分成多少块瓦片
  //            计算每块瓦片的宽和高
        let nw = ~~(width / count);
        let nh = ~~(height / count);
        tCanvas.width = nw;
        tCanvas.height = nh;
        for (let i = 0; i < count; i++) {
          for (let j = 0; j < count; j++) {
            tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
            ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
          }
        }
      } else {
        ctx.drawImage(img, 0, 0, width, height);
      }
      //修复ios上传图片的时候 被旋转的问题
      if(Orientation != "" && Orientation != 1){
        switch(Orientation){
          case 6://需要顺时针（向左）90度旋转
              this.rotateImg(img,'left',canvas);
              break;
          case 8://需要逆时针（向右）90度旋转
              this.rotateImg(img,'right',canvas);
              break;
          case 3://需要180度旋转
              this.rotateImg(img,'right',canvas);//转两次
              this.rotateImg(img,'right',canvas);
              break;
        }
      }
      //进行最小压缩
      let ndata = canvas.toDataURL('image/jpeg', 0.1);
      console.log('压缩前：' + initSize);
      console.log('压缩后：' + ndata.length);
      console.log('压缩率：' + ~~(100 * (initSize - ndata.length) / initSize) + "%");
      tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
      return ndata;
    },
  }
}
script>

<style>
*{
  margin: 0;
  padding: 0;
}
.show {
  width: 100px;
  height: 100px;
  overflow: hidden;
  position: relative;
  border-radius: 50%;
  border: 1px solid #d5d5d5;
}
.picture {
  width: 100%;
  height: 100%;
  overflow: hidden;
  background-position: center center;
  background-repeat: no-repeat;
  background-size: cover;
}
style>

引用的exif.js代码

(function() {

    var debug = false;

    var root = this;

    var EXIF = function(obj) {
        if (obj instanceof EXIF) return obj;
        if (!(this instanceof EXIF)) return new EXIF(obj);
        this.EXIFwrapped = obj;
    };

    if (typeof exports !== 'undefined') {
        if (typeof module !== 'undefined' && module.exports) {
            exports = module.exports = EXIF;
        }
        exports.EXIF = EXIF;
    } else {
        root.EXIF = EXIF;
    }

    var ExifTags = EXIF.Tags = {

        // version tags
        0x9000 : "ExifVersion",             // EXIF version
        0xA000 : "FlashpixVersion",         // Flashpix format version

        // colorspace tags
        0xA001 : "ColorSpace",              // Color space information tag

        // image configuration
        0xA002 : "PixelXDimension",         // Valid width of meaningful image
        0xA003 : "PixelYDimension",         // Valid height of meaningful image
        0x9101 : "ComponentsConfiguration", // Information about channels
        0x9102 : "CompressedBitsPerPixel",  // Compressed bits per pixel

        // user information
        0x927C : "MakerNote",               // Any desired information written by the manufacturer
        0x9286 : "UserComment",             // Comments by user

        // related file
        0xA004 : "RelatedSoundFile",        // Name of related sound file

        // date and time
        0x9003 : "DateTimeOriginal",        // Date and time when the original image was generated
        0x9004 : "DateTimeDigitized",       // Date and time when the image was stored digitally
        0x9290 : "SubsecTime",              // Fractions of seconds for DateTime
        0x9291 : "SubsecTimeOriginal",      // Fractions of seconds for DateTimeOriginal
        0x9292 : "SubsecTimeDigitized",     // Fractions of seconds for DateTimeDigitized

        // picture-taking conditions
        0x829A : "ExposureTime",            // Exposure time (in seconds)
        0x829D : "FNumber",                 // F number
        0x8822 : "ExposureProgram",         // Exposure program
        0x8824 : "SpectralSensitivity",     // Spectral sensitivity
        0x8827 : "ISOSpeedRatings",         // ISO speed rating
        0x8828 : "OECF",                    // Optoelectric conversion factor
        0x9201 : "ShutterSpeedValue",       // Shutter speed
        0x9202 : "ApertureValue",           // Lens aperture
        0x9203 : "BrightnessValue",         // Value of brightness
        0x9204 : "ExposureBias",            // Exposure bias
        0x9205 : "MaxApertureValue",        // Smallest F number of lens
        0x9206 : "SubjectDistance",         // Distance to subject in meters
        0x9207 : "MeteringMode",            // Metering mode
        0x9208 : "LightSource",             // Kind of light source
        0x9209 : "Flash",                   // Flash status
        0x9214 : "SubjectArea",             // Location and area of main subject
        0x920A : "FocalLength",             // Focal length of the lens in mm
        0xA20B : "FlashEnergy",             // Strobe energy in BCPS
        0xA20C : "SpatialFrequencyResponse",    //
        0xA20E : "FocalPlaneXResolution",   // Number of pixels in width direction per FocalPlaneResolutionUnit
        0xA20F : "FocalPlaneYResolution",   // Number of pixels in height direction per FocalPlaneResolutionUnit
        0xA210 : "FocalPlaneResolutionUnit",    // Unit for measuring FocalPlaneXResolution and FocalPlaneYResolution
        0xA214 : "SubjectLocation",         // Location of subject in image
        0xA215 : "ExposureIndex",           // Exposure index selected on camera
        0xA217 : "SensingMethod",           // Image sensor type
        0xA300 : "FileSource",              // Image source (3 == DSC)
        0xA301 : "SceneType",               // Scene type (1 == directly photographed)
        0xA302 : "CFAPattern",              // Color filter array geometric pattern
        0xA401 : "CustomRendered",          // Special processing
        0xA402 : "ExposureMode",            // Exposure mode
        0xA403 : "WhiteBalance",            // 1 = auto white balance, 2 = manual
        0xA404 : "DigitalZoomRation",       // Digital zoom ratio
        0xA405 : "FocalLengthIn35mmFilm",   // Equivalent foacl length assuming 35mm film camera (in mm)
        0xA406 : "SceneCaptureType",        // Type of scene
        0xA407 : "GainControl",             // Degree of overall image gain adjustment
        0xA408 : "Contrast",                // Direction of contrast processing applied by camera
        0xA409 : "Saturation",              // Direction of saturation processing applied by camera
        0xA40A : "Sharpness",               // Direction of sharpness processing applied by camera
        0xA40B : "DeviceSettingDescription",    //
        0xA40C : "SubjectDistanceRange",    // Distance to subject

        // other tags
        0xA005 : "InteroperabilityIFDPointer",
        0xA420 : "ImageUniqueID"            // Identifier assigned uniquely to each image
    };

    var TiffTags = EXIF.TiffTags = {
        0x0100 : "ImageWidth",
        0x0101 : "ImageHeight",
        0x8769 : "ExifIFDPointer",
        0x8825 : "GPSInfoIFDPointer",
        0xA005 : "InteroperabilityIFDPointer",
        0x0102 : "BitsPerSample",
        0x0103 : "Compression",
        0x0106 : "PhotometricInterpretation",
        0x0112 : "Orientation",
        0x0115 : "SamplesPerPixel",
        0x011C : "PlanarConfiguration",
        0x0212 : "YCbCrSubSampling",
        0x0213 : "YCbCrPositioning",
        0x011A : "XResolution",
        0x011B : "YResolution",
        0x0128 : "ResolutionUnit",
        0x0111 : "StripOffsets",
        0x0116 : "RowsPerStrip",
        0x0117 : "StripByteCounts",
        0x0201 : "JPEGInterchangeFormat",
        0x0202 : "JPEGInterchangeFormatLength",
        0x012D : "TransferFunction",
        0x013E : "WhitePoint",
        0x013F : "PrimaryChromaticities",
        0x0211 : "YCbCrCoefficients",
        0x0214 : "ReferenceBlackWhite",
        0x0132 : "DateTime",
        0x010E : "ImageDescription",
        0x010F : "Make",
        0x0110 : "Model",
        0x0131 : "Software",
        0x013B : "Artist",
        0x8298 : "Copyright"
    };

    var GPSTags = EXIF.GPSTags = {
        0x0000 : "GPSVersionID",
        0x0001 : "GPSLatitudeRef",
        0x0002 : "GPSLatitude",
        0x0003 : "GPSLongitudeRef",
        0x0004 : "GPSLongitude",
        0x0005 : "GPSAltitudeRef",
        0x0006 : "GPSAltitude",
        0x0007 : "GPSTimeStamp",
        0x0008 : "GPSSatellites",
        0x0009 : "GPSStatus",
        0x000A : "GPSMeasureMode",
        0x000B : "GPSDOP",
        0x000C : "GPSSpeedRef",
        0x000D : "GPSSpeed",
        0x000E : "GPSTrackRef",
        0x000F : "GPSTrack",
        0x0010 : "GPSImgDirectionRef",
        0x0011 : "GPSImgDirection",
        0x0012 : "GPSMapDatum",
        0x0013 : "GPSDestLatitudeRef",
        0x0014 : "GPSDestLatitude",
        0x0015 : "GPSDestLongitudeRef",
        0x0016 : "GPSDestLongitude",
        0x0017 : "GPSDestBearingRef",
        0x0018 : "GPSDestBearing",
        0x0019 : "GPSDestDistanceRef",
        0x001A : "GPSDestDistance",
        0x001B : "GPSProcessingMethod",
        0x001C : "GPSAreaInformation",
        0x001D : "GPSDateStamp",
        0x001E : "GPSDifferential"
    };

    var StringValues = EXIF.StringValues = {
        ExposureProgram : {
            0 : "Not defined",
            1 : "Manual",
            2 : "Normal program",
            3 : "Aperture priority",
            4 : "Shutter priority",
            5 : "Creative program",
            6 : "Action program",
            7 : "Portrait mode",
            8 : "Landscape mode"
        },
        MeteringMode : {
            0 : "Unknown",
            1 : "Average",
            2 : "CenterWeightedAverage",
            3 : "Spot",
            4 : "MultiSpot",
            5 : "Pattern",
            6 : "Partial",
            255 : "Other"
        },
        LightSource : {
            0 : "Unknown",
            1 : "Daylight",
            2 : "Fluorescent",
            3 : "Tungsten (incandescent light)",
            4 : "Flash",
            9 : "Fine weather",
            10 : "Cloudy weather",
            11 : "Shade",
            12 : "Daylight fluorescent (D 5700 - 7100K)",
            13 : "Day white fluorescent (N 4600 - 5400K)",
            14 : "Cool white fluorescent (W 3900 - 4500K)",
            15 : "White fluorescent (WW 3200 - 3700K)",
            17 : "Standard light A",
            18 : "Standard light B",
            19 : "Standard light C",
            20 : "D55",
            21 : "D65",
            22 : "D75",
            23 : "D50",
            24 : "ISO studio tungsten",
            255 : "Other"
        },
        Flash : {
            0x0000 : "Flash did not fire",
            0x0001 : "Flash fired",
            0x0005 : "Strobe return light not detected",
            0x0007 : "Strobe return light detected",
            0x0009 : "Flash fired, compulsory flash mode",
            0x000D : "Flash fired, compulsory flash mode, return light not detected",
            0x000F : "Flash fired, compulsory flash mode, return light detected",
            0x0010 : "Flash did not fire, compulsory flash mode",
            0x0018 : "Flash did not fire, auto mode",
            0x0019 : "Flash fired, auto mode",
            0x001D : "Flash fired, auto mode, return light not detected",
            0x001F : "Flash fired, auto mode, return light detected",
            0x0020 : "No flash function",
            0x0041 : "Flash fired, red-eye reduction mode",
            0x0045 : "Flash fired, red-eye reduction mode, return light not detected",
            0x0047 : "Flash fired, red-eye reduction mode, return light detected",
            0x0049 : "Flash fired, compulsory flash mode, red-eye reduction mode",
            0x004D : "Flash fired, compulsory flash mode, red-eye reduction mode, return light not detected",
            0x004F : "Flash fired, compulsory flash mode, red-eye reduction mode, return light detected",
            0x0059 : "Flash fired, auto mode, red-eye reduction mode",
            0x005D : "Flash fired, auto mode, return light not detected, red-eye reduction mode",
            0x005F : "Flash fired, auto mode, return light detected, red-eye reduction mode"
        },
        SensingMethod : {
            1 : "Not defined",
            2 : "One-chip color area sensor",
            3 : "Two-chip color area sensor",
            4 : "Three-chip color area sensor",
            5 : "Color sequential area sensor",
            7 : "Trilinear sensor",
            8 : "Color sequential linear sensor"
        },
        SceneCaptureType : {
            0 : "Standard",
            1 : "Landscape",
            2 : "Portrait",
            3 : "Night scene"
        },
        SceneType : {
            1 : "Directly photographed"
        },
        CustomRendered : {
            0 : "Normal process",
            1 : "Custom process"
        },
        WhiteBalance : {
            0 : "Auto white balance",
            1 : "Manual white balance"
        },
        GainControl : {
            0 : "None",
            1 : "Low gain up",
            2 : "High gain up",
            3 : "Low gain down",
            4 : "High gain down"
        },
        Contrast : {
            0 : "Normal",
            1 : "Soft",
            2 : "Hard"
        },
        Saturation : {
            0 : "Normal",
            1 : "Low saturation",
            2 : "High saturation"
        },
        Sharpness : {
            0 : "Normal",
            1 : "Soft",
            2 : "Hard"
        },
        SubjectDistanceRange : {
            0 : "Unknown",
            1 : "Macro",
            2 : "Close view",
            3 : "Distant view"
        },
        FileSource : {
            3 : "DSC"
        },

        Components : {
            0 : "",
            1 : "Y",
            2 : "Cb",
            3 : "Cr",
            4 : "R",
            5 : "G",
            6 : "B"
        }
    };

    function addEvent(element, event, handler) {
        if (element.addEventListener) {
            element.addEventListener(event, handler, false);
        } else if (element.attachEvent) {
            element.attachEvent("on" + event, handler);
        }
    }

    function imageHasData(img) {
        return !!(img.exifdata);
    }


    function base64ToArrayBuffer(base64, contentType) {
        contentType = contentType || base64.match(/^data\:([^\;]+)\;base64,/mi)[1] || ''; // e.g. 'data:image/jpeg;base64,...' => 'image/jpeg'
        base64 = base64.replace(/^data\:([^\;]+)\;base64,/gmi, '');
        var binary = atob(base64);
        var len = binary.length;
        var buffer = new ArrayBuffer(len);
        var view = new Uint8Array(buffer);
        for (var i = 0; i < len; i++) {
            view[i] = binary.charCodeAt(i);
        }
        return buffer;
    }

    function objectURLToBlob(url, callback) {
        var http = new XMLHttpRequest();
        http.open("GET", url, true);
        http.responseType = "blob";
        http.onload = function(e) {
            if (this.status == 200 || this.status === 0) {
                callback(this.response);
            }
        };
        http.send();
    }

    function getImageData(img, callback) {
        function handleBinaryFile(binFile) {
            var data = findEXIFinJPEG(binFile);
            var iptcdata = findIPTCinJPEG(binFile);
            img.exifdata = data || {};
            img.iptcdata = iptcdata || {};
            if (callback) {
                callback.call(img);
            }
        }

        if (img.src) {
            if (/^data\:/i.test(img.src)) { // Data URI
                var arrayBuffer = base64ToArrayBuffer(img.src);
                handleBinaryFile(arrayBuffer);

            } else if (/^blob\:/i.test(img.src)) { // Object URL
                var fileReader = new FileReader();
                fileReader.onload = function(e) {
                    handleBinaryFile(e.target.result);
                };
                objectURLToBlob(img.src, function (blob) {
                    fileReader.readAsArrayBuffer(blob);
                });
            } else {
                var http = new XMLHttpRequest();
                http.onload = function() {
                    if (this.status == 200 || this.status === 0) {
                        handleBinaryFile(http.response);
                    } else {
                        throw "Could not load image";
                    }
                    http = null;
                };
                http.open("GET", img.src, true);
                http.responseType = "arraybuffer";
                http.send(null);
            }
        } else if (window.FileReader && (img instanceof window.Blob || img instanceof window.File)) {
            var fileReader = new FileReader();
            fileReader.onload = function(e) {
                if (debug) console.log("Got file of length " + e.target.result.byteLength);
                handleBinaryFile(e.target.result);
            };

            fileReader.readAsArrayBuffer(img);
        }
    }

    function findEXIFinJPEG(file) {
        var dataView = new DataView(file);

        if (debug) console.log("Got file of length " + file.byteLength);
        if ((dataView.getUint8(0) != 0xFF) || (dataView.getUint8(1) != 0xD8)) {
            if (debug) console.log("Not a valid JPEG");
            return false; // not a valid jpeg
        }

        var offset = 2,
            length = file.byteLength,
            marker;

        while (offset < length) {
            if (dataView.getUint8(offset) != 0xFF) {
                if (debug) console.log("Not a valid marker at offset " + offset + ", found: " + dataView.getUint8(offset));
                return false; // not a valid marker, something is wrong
            }

            marker = dataView.getUint8(offset + 1);
            if (debug) console.log(marker);

            // we could implement handling for other markers here,
            // but we're only looking for 0xFFE1 for EXIF data

            if (marker == 225) {
                if (debug) console.log("Found 0xFFE1 marker");

                return readEXIFData(dataView, offset + 4, dataView.getUint16(offset + 2) - 2);

                // offset += 2 + file.getShortAt(offset+2, true);

            } else {
                offset += 2 + dataView.getUint16(offset+2);
            }

        }

    }

    function findIPTCinJPEG(file) {
        var dataView = new DataView(file);

        if (debug) console.log("Got file of length " + file.byteLength);
        if ((dataView.getUint8(0) != 0xFF) || (dataView.getUint8(1) != 0xD8)) {
            if (debug) console.log("Not a valid JPEG");
            return false; // not a valid jpeg
        }

        var offset = 2,
            length = file.byteLength;


        var isFieldSegmentStart = function(dataView, offset){
            return (
                dataView.getUint8(offset) === 0x38 &&
                dataView.getUint8(offset+1) === 0x42 &&
                dataView.getUint8(offset+2) === 0x49 &&
                dataView.getUint8(offset+3) === 0x4D &&
                dataView.getUint8(offset+4) === 0x04 &&
                dataView.getUint8(offset+5) === 0x04
            );
        };

        while (offset < length) {

            if ( isFieldSegmentStart(dataView, offset )){

                // Get the length of the name header (which is padded to an even number of bytes)
                var nameHeaderLength = dataView.getUint8(offset+7);
                if(nameHeaderLength % 2 !== 0) nameHeaderLength += 1;
                // Check for pre photoshop 6 format
                if(nameHeaderLength === 0) {
                    // Always 4
                    nameHeaderLength = 4;
                }

                var startOffset = offset + 8 + nameHeaderLength;
                var sectionLength = dataView.getUint16(offset + 6 + nameHeaderLength);

                return readIPTCData(file, startOffset, sectionLength);

                break;

            }


            // Not the marker, continue searching
            offset++;

        }

    }
    var IptcFieldMap = {
        0x78 : 'caption',
        0x6E : 'credit',
        0x19 : 'keywords',
        0x37 : 'dateCreated',
        0x50 : 'byline',
        0x55 : 'bylineTitle',
        0x7A : 'captionWriter',
        0x69 : 'headline',
        0x74 : 'copyright',
        0x0F : 'category'
    };
    function readIPTCData(file, startOffset, sectionLength){
        var dataView = new DataView(file);
        var data = {};
        var fieldValue, fieldName, dataSize, segmentType, segmentSize;
        var segmentStartPos = startOffset;
        while(segmentStartPos < startOffset+sectionLength) {
            if(dataView.getUint8(segmentStartPos) === 0x1C && dataView.getUint8(segmentStartPos+1) === 0x02){
                segmentType = dataView.getUint8(segmentStartPos+2);
                if(segmentType in IptcFieldMap) {
                    dataSize = dataView.getInt16(segmentStartPos+3);
                    segmentSize = dataSize + 5;
                    fieldName = IptcFieldMap[segmentType];
                    fieldValue = getStringFromDB(dataView, segmentStartPos+5, dataSize);
                    // Check if we already stored a value with this name
                    if(data.hasOwnProperty(fieldName)) {
                        // Value already stored with this name, create multivalue field
                        if(data[fieldName] instanceof Array) {
                            data[fieldName].push(fieldValue);
                        }
                        else {
                            data[fieldName] = [data[fieldName], fieldValue];
                        }
                    }
                    else {
                        data[fieldName] = fieldValue;
                    }
                }

            }
            segmentStartPos++;
        }
        return data;
    }



    function readTags(file, tiffStart, dirStart, strings, bigEnd) {
        var entries = file.getUint16(dirStart, !bigEnd),
            tags = {},
            entryOffset, tag,
            i;

        for (i=0;i<entries;i++) {
            entryOffset = dirStart + i*12 + 2;
            tag = strings[file.getUint16(entryOffset, !bigEnd)];
            if (!tag && debug) console.log("Unknown tag: " + file.getUint16(entryOffset, !bigEnd));
            tags[tag] = readTagValue(file, entryOffset, tiffStart, dirStart, bigEnd);
        }
        return tags;
    }


    function readTagValue(file, entryOffset, tiffStart, dirStart, bigEnd) {
        var type = file.getUint16(entryOffset+2, !bigEnd),
            numValues = file.getUint32(entryOffset+4, !bigEnd),
            valueOffset = file.getUint32(entryOffset+8, !bigEnd) + tiffStart,
            offset,
            vals, val, n,
            numerator, denominator;

        switch (type) {
            case 1: // byte, 8-bit unsigned int
            case 7: // undefined, 8-bit byte, value depending on field
                if (numValues == 1) {
                    return file.getUint8(entryOffset + 8, !bigEnd);
                } else {
                    offset = numValues > 4 ? valueOffset : (entryOffset + 8);
                    vals = [];
                    for (n=0;n<numValues;n++) {
                        vals[n] = file.getUint8(offset + n);
                    }
                    return vals;
                }

            case 2: // ascii, 8-bit byte
                offset = numValues > 4 ? valueOffset : (entryOffset + 8);
                return getStringFromDB(file, offset, numValues-1);

            case 3: // short, 16 bit int
                if (numValues == 1) {
                    return file.getUint16(entryOffset + 8, !bigEnd);
                } else {
                    offset = numValues > 2 ? valueOffset : (entryOffset + 8);
                    vals = [];
                    for (n=0;n<numValues;n++) {
                        vals[n] = file.getUint16(offset + 2*n, !bigEnd);
                    }
                    return vals;
                }

            case 4: // long, 32 bit int
                if (numValues == 1) {
                    return file.getUint32(entryOffset + 8, !bigEnd);
                } else {
                    vals = [];
                    for (n=0;n<numValues;n++) {
                        vals[n] = file.getUint32(valueOffset + 4*n, !bigEnd);
                    }
                    return vals;
                }

            case 5:    // rational = two long values, first is numerator, second is denominator
                if (numValues == 1) {
                    numerator = file.getUint32(valueOffset, !bigEnd);
                    denominator = file.getUint32(valueOffset+4, !bigEnd);
                    val = new Number(numerator / denominator);
                    val.numerator = numerator;
                    val.denominator = denominator;
                    return val;
                } else {
                    vals = [];
                    for (n=0;n<numValues;n++) {
                        numerator = file.getUint32(valueOffset + 8*n, !bigEnd);
                        denominator = file.getUint32(valueOffset+4 + 8*n, !bigEnd);
                        vals[n] = new Number(numerator / denominator);
                        vals[n].numerator = numerator;
                        vals[n].denominator = denominator;
                    }
                    return vals;
                }

            case 9: // slong, 32 bit signed int
                if (numValues == 1) {
                    return file.getInt32(entryOffset + 8, !bigEnd);
                } else {
                    vals = [];
                    for (n=0;n<numValues;n++) {
                        vals[n] = file.getInt32(valueOffset + 4*n, !bigEnd);
                    }
                    return vals;
                }

            case 10: // signed rational, two slongs, first is numerator, second is denominator
                if (numValues == 1) {
                    return file.getInt32(valueOffset, !bigEnd) / file.getInt32(valueOffset+4, !bigEnd);
                } else {
                    vals = [];
                    for (n=0;n<numValues;n++) {
                        vals[n] = file.getInt32(valueOffset + 8*n, !bigEnd) / file.getInt32(valueOffset+4 + 8*n, !bigEnd);
                    }
                    return vals;
                }
        }
    }

    function getStringFromDB(buffer, start, length) {
        var outstr = "";
        for (n = start; n < start+length; n++) {
            outstr += String.fromCharCode(buffer.getUint8(n));
        }
        return outstr;
    }

    function readEXIFData(file, start) {
        if (getStringFromDB(file, start, 4) != "Exif") {
            if (debug) console.log("Not valid EXIF data! " + getStringFromDB(file, start, 4));
            return false;
        }

        var bigEnd,
            tags, tag,
            exifData, gpsData,
            tiffOffset = start + 6;

        // test for TIFF validity and endianness
        if (file.getUint16(tiffOffset) == 0x4949) {
            bigEnd = false;
        } else if (file.getUint16(tiffOffset) == 0x4D4D) {
            bigEnd = true;
        } else {
            if (debug) console.log("Not valid TIFF data! (no 0x4949 or 0x4D4D)");
            return false;
        }

        if (file.getUint16(tiffOffset+2, !bigEnd) != 0x002A) {
            if (debug) console.log("Not valid TIFF data! (no 0x002A)");
            return false;
        }

        var firstIFDOffset = file.getUint32(tiffOffset+4, !bigEnd);

        if (firstIFDOffset < 0x00000008) {
            if (debug) console.log("Not valid TIFF data! (First offset less than 8)", file.getUint32(tiffOffset+4, !bigEnd));
            return false;
        }

        tags = readTags(file, tiffOffset, tiffOffset + firstIFDOffset, TiffTags, bigEnd);

        if (tags.ExifIFDPointer) {
            exifData = readTags(file, tiffOffset, tiffOffset + tags.ExifIFDPointer, ExifTags, bigEnd);
            for (tag in exifData) {
                switch (tag) {
                    case "LightSource" :
                    case "Flash" :
                    case "MeteringMode" :
                    case "ExposureProgram" :
                    case "SensingMethod" :
                    case "SceneCaptureType" :
                    case "SceneType" :
                    case "CustomRendered" :
                    case "WhiteBalance" :
                    case "GainControl" :
                    case "Contrast" :
                    case "Saturation" :
                    case "Sharpness" :
                    case "SubjectDistanceRange" :
                    case "FileSource" :
                        exifData[tag] = StringValues[tag][exifData[tag]];
                        break;

                    case "ExifVersion" :
                    case "FlashpixVersion" :
                        exifData[tag] = String.fromCharCode(exifData[tag][0], exifData[tag][1], exifData[tag][2], exifData[tag][3]);
                        break;

                    case "ComponentsConfiguration" :
                        exifData[tag] =
                            StringValues.Components[exifData[tag][0]] +
                            StringValues.Components[exifData[tag][1]] +
                            StringValues.Components[exifData[tag][2]] +
                            StringValues.Components[exifData[tag][3]];
                        break;
                }
                tags[tag] = exifData[tag];
            }
        }

        if (tags.GPSInfoIFDPointer) {
            gpsData = readTags(file, tiffOffset, tiffOffset + tags.GPSInfoIFDPointer, GPSTags, bigEnd);
            for (tag in gpsData) {
                switch (tag) {
                    case "GPSVersionID" :
                        gpsData[tag] = gpsData[tag][0] +
                            "." + gpsData[tag][1] +
                            "." + gpsData[tag][2] +
                            "." + gpsData[tag][3];
                        break;
                }
                tags[tag] = gpsData[tag];
            }
        }

        return tags;
    }

    EXIF.getData = function(img, callback) {
        if ((img instanceof Image || img instanceof HTMLImageElement) && !img.complete) return false;

        if (!imageHasData(img)) {
            getImageData(img, callback);
        } else {
            if (callback) {
                callback.call(img);
            }
        }
        return true;
    }

    EXIF.getTag = function(img, tag) {
        if (!imageHasData(img)) return;
        return img.exifdata[tag];
    }

    EXIF.getAllTags = function(img) {
        if (!imageHasData(img)) return {};
        var a,
            data = img.exifdata,
            tags = {};
        for (a in data) {
            if (data.hasOwnProperty(a)) {
                tags[a] = data[a];
            }
        }
        return tags;
    }

    EXIF.pretty = function(img) {
        if (!imageHasData(img)) return "";
        var a,
            data = img.exifdata,
            strPretty = "";
        for (a in data) {
            if (data.hasOwnProperty(a)) {
                if (typeof data[a] == "object") {
                    if (data[a] instanceof Number) {
                        strPretty += a + " : " + data[a] + " [" + data[a].numerator + "/" + data[a].denominator + "]\r\n";
                    } else {
                        strPretty += a + " : [" + data[a].length + " values]\r\n";
                    }
                } else {
                    strPretty += a + " : " + data[a] + "\r\n";
                }
            }
        }
        return strPretty;
    }

    EXIF.readFromBinaryFile = function(file) {
        return findEXIFinJPEG(file);
    }

    if (typeof define === 'function' && define.amd) {
        define('exif-js', [], function() {
            return EXIF;
        });
    }
}.call(this));