A JavaScript library for reading EXIF meta data from image files.

exif-js/exif-js: JavaScript library for reading EXIF image metadata https://github.com/exif-js/exif-js

exif-js - npm https://www.npmjs.com/package/exif-js

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>EXIF example with inline EXIF info</title>

</head>

<body>

    <img src="DSCN0614_small.jpg" id="img1" />

    <pre>Make and model: <span id="makeAndModel"></span></div>

    <br/>

    <img src="Bush-dog.jpg" id="img2" />

    <pre id="allMetaDataSpan"></pre>

    <br/>

    <img src="Bloated-Hero.jpg" id="img3" /><br/>

    <pre id="img3WithXmpMetaData"></pre>

    <script type="text/javascript" src="../exif.js"></script>

    <script>

        "use strict";

        window.onload=getExif;

        function getExif() {

            var img1 = document.getElementById("img1");

            EXIF.getData(img1, function() {

                var make = EXIF.getTag(this, "Make");

                var model = EXIF.getTag(this, "Model");

                var makeAndModel = document.getElementById("makeAndModel");

                makeAndModel.innerHTML = `${make} ${model}`;

            });

            var img2 = document.getElementById("img2");

            EXIF.getData(img2, function() {

                var allMetaData = EXIF.getAllTags(this);

                var allMetaDataSpan = document.getElementById("allMetaDataSpan");

                allMetaDataSpan.innerHTML = JSON.stringify(allMetaData, null, "\t");

            });

            var img3 = document.getElementById("img3");

            // EXIF.enableXmp();

            EXIF.getData(img3, function() {

                var allMetaData = EXIF.getAllTags(this);

                var img3WithXmpMetaData = document.getElementById("img3WithXmpMetaData");

                img3WithXmpMetaData.innerHTML = JSON.stringify(allMetaData, null, "\t");

            });

        }

    </script>

</body>

</html>

vue2移动端上传，预览，压缩图片，解决拍照旋转问题 - CSDN博客 https://blog.csdn.net/xiaogezl/article/details/70156500

2017年04月13日 11:32:00

阅读数：6183

因为最近遇到个移动端上传头像的需求，上传到后台的数据是base64位，其中为了提高用户体验，把比较大的图片用canvas进行压缩之后再进行上传。在移动端调用拍照功能时，会发生图片旋转，为了解决这个问题引入了exif去判断拍照时的信息再去处理图片，这是个很好的插件。关于exif.js可以去他的GitHub上了解，这边直接npm install exif-js --save 安装，然后import一下就可以使用了。以下就是源码，可以直接使用。

<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" @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);

    },

    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>

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