JS 图片研究笔记

这几天，对图片进行了大量的研究。

获取图片的真实大小

const img = new Image();
img.src = 'https://www.baidu.com/img/bd_logo1.png';
img.onload = () => {
  console.log(img.width, img.height);
};

但是，这个方法可能获取到得是图片的显示大小，而不是真实大小。真实大小可以用 img.naturalWidth 和 img.naturalHeight 来获取。

const img = new Image();
img.src = 'https://www.baidu.com/img/bd_logo1.png';
img.onload = () => {
  console.log(img.naturalWidth, img.naturalHeight);
};

提取 Exif 数据

可以用 exif-js 库 - https://github.com/exif-js/exif-js

const EXIF = require('exif-js');
const img = new Image();
img.src = 'https://www.baidu.com/img/bd_logo1.png';
img.onload = () => {
  EXIF.getData(img, function () {
    const allMetaData = EXIF.getAllTags(this);
    console.log(allMetaData);
  });
};

设置图片的 Exif 信息

可以用 Piexifjs 库 - https://github.com/hMatoba/piexifjs

这个文章做了大量的研究和介绍 - https://auth0.com/blog/read-edit-exif-metadata-in-photos-with-javascript/

npm install piexifjs@1.0.4

import piexifjs from 'piexifjs';
// let tiff = {};
// let gps = {};
// tiff[piexif.ImageIFD.Make] = key;//生产商
// tiff[piexif.ImageIFD.Model] = key;//型号
// tiff[piexif.ImageIFD.DateTime] = key;//日期
// tiff[piexif.ImageIFD.Artist] = key;//作者
// tiff[piexif.ImageIFD.ImageWidth] = key;//图像宽度
// tiff[piexif.ImageIFD.ImageHeight] = key;//图像高度
// gps["GPSVersionID": key];//GPS版本
// gps["GPSLatitude": key];//纬度
// gps["GPSLongitude": key];//经度
// gps["GPSAltitude": key];//海拔
// gps["GPSDestBearing": key];//目标方位
// gps["GPSDestDistance": key];//目标距离
// let exifObj = {"tiff":tiff,"gps":gps};
// let exifStr = piexif.dump(exifObj);//获取exif信息字符串
// let resultBase64 = piexif.insert(exifStr, base64);//将exif信息插入到base64中

document.getElementById('saveButton').onclick = function () {
  // make exif data
  var zerothIfd = {};
  var exifIfd = {};
  var gpsIfd = {};
  zerothIfd[piexif.ImageIFD.Make] = 'Maker Name';
  zerothIfd[piexif.ImageIFD.XResolution] = [777, 1];
  zerothIfd[piexif.ImageIFD.YResolution] = [777, 1];
  zerothIfd[piexif.ImageIFD.Software] = 'Piexifjs';
  exifIfd[piexif.ExifIFD.DateTimeOriginal] = '2010:10:10 10:10:10';
  exifIfd[piexif.ExifIFD.LensMake] = 'Lens Maker';
  exifIfd[piexif.ExifIFD.Sharpness] = 777;
  exifIfd[piexif.ExifIFD.LensSpecification] = [
    [1, 1],
    [1, 1],
    [1, 1],
    [1, 1],
  ];
  gpsIfd[piexif.GPSIFD.GPSVersionID] = [7, 7, 7, 7];
  gpsIfd[piexif.GPSIFD.GPSDateStamp] = '1999:99:99 99:99:99';

  var lat = 59.43553989213321;
  var lng = 24.73842144012451;
  gpsIfd[piexif.GPSIFD.GPSLatitudeRef] = lat < 0 ? 'S' : 'N';
  gpsIfd[piexif.GPSIFD.GPSLatitude] = piexif.GPSHelper.degToDmsRational(lat);
  gpsIfd[piexif.GPSIFD.GPSLongitudeRef] = lng < 0 ? 'W' : 'E';
  gpsIfd[piexif.GPSIFD.GPSLongitude] = piexif.GPSHelper.degToDmsRational(lng);

  var exifObj = { '0th': zerothIfd, Exif: exifIfd, GPS: gpsIfd };

  // get exif binary as "string" type
  var exifBytes = piexif.dump(exifObj);

  // get JPEG image from canvas
  var jpegData = document.getElementById('canvas').toDataURL('image/jpeg', 1.0);

  // insert exif binary into JPEG binary(DataURL)
  var exifModified = piexif.insert(exifBytes, jpegData);

  // show JPEG modified exif
  var image = new Image();
  image.src = exifModified;
  image.width = 200;
  // for Modern IE
  if (saveJpeg) {
    var jpegBinary = atob(exifModified.split(',')[1]);
    var data = [];
    for (var p = 0; p < jpegBinary.length; p++) {
      data[p] = jpegBinary.charCodeAt(p);
    }
    var ua = new Uint8Array(data);
    var blob = new Blob([ua], { type: 'image/jpeg' });
    image.onclick = saveJpeg(blob);
  }
  var el = $('<div></div>').append(image);
  $('#resized').prepend(el);
};

裁剪图片（浏览器）

可以用 cropper.js 库 -

裁剪图片（NodeJS) - sharp

npm install sharp

import sharp from 'sharp';
sharp('input.jpg')
  .resize(200, 300)
  .toFile('output.jpg', (err, info) => {
    // output.jpg is a 200 pixels wide and 300 pixels high image
    // containing a scaled and cropped version of input.jpg
  });

微信小程序提取图片 base64

参考文章：

• 微信小程序提取图片 base64
• 还有转成 blob 上传
• https://blog.csdn.net/qq_36875339/article/details/81086205
• https://zhuanlan.zhihu.com/p/38593007
• https://www.cnblogs.com/china-fanny/p/11213746.html
• http://blog.mokevip.top/2021/04/01/miniprogram-picture-code/
• https://juejin.cn/post/7055597030642548772
• https://juejin.cn/post/6934956172160008223

wx.canvasToTempFilePath({
  canvasId: 'canvas',
  success: function (res) {
    console.log(res.tempFilePath);
    wx.getFileSystemManager().readFile({
      filePath: res.tempFilePath,
      encoding: 'base64',
      success: (res) => {
        console.log(res.data);
      },
    });
  },
});

上面这个方法有个问题，就是它给出的 base64 为 png 格式，而不是 jpg 格式

但是后来我发现一些更好的方法，可以直接获取 jpg 格式的 base64

wx.canvasGetImageData({
  canvasId: 'canvas',
  x: 0,
  y: 0,
  width: 100,
  height: 100,
  success: function (res) {
    console.log(res.data);
  },
});

微信小程序- 本地临时文件转 base64

// 本地文件转base64
function wxfileTobase64(url, ishead = false) {
  return new Promise((reslove, reject) => {
    wx.getFileSystemManager().readFile({
      filePath: url, //选择图片返回的相对路径
      encoding: 'base64', //编码格式
      success: (res) => {
        //成功的回调
        reslove((ishead ? 'data:image/jpeg;base64,' : '') + res.data);
      },
      fail: (err) => {
        reject(err);
      },
    });
  });
}
// 使用
wx.chooseImage({
  count: 4,
  sizeType: ['compressed'],
  sourceType: ['album', 'camera'],
  success(res) {
    wxfileTobase64(res.tempFilePaths[0]).then((base64) => {
      console.log(base64);
    });
  },
});

微信小程序 - base64 转本地临时文件

function base64ToWxfile(base64, fileName) {
  const path = wx.env.USER_DATA_PATH + '/' + fileName;
  return new Promise((reslove, reject) => {
    wx.getFileSystemManager().writeFile({
      filePath: path,
      data: base64,
      encoding: 'base64',
      success: (res) => {
        reslove(path);
      },
      fail: (err) => {
        reject(err);
      },
    });
  });
}

微信小程序 - URL 转 base64

function urlTobase64(url, ishead = false) {
  return new Promise((reslove, reject) => {
    wx.request({
      url: url,
      responseType: 'arraybuffer', //最关键的参数，设置返回的数据格式为arraybuffer
      success: (res) => {
        //把arraybuffer转成base64
        let base64 = wx.arrayBufferToBase64(res.data);

        //不加上这串字符，在页面无法显示的哦
        base64 = (ishead ? 'data:image/jpeg;base64,' : '') + base64;

        //打印出base64字符串，可复制到网页校验一下是否是你选择的原图片呢
        reslove(base64);
      },
    });
  });
}

微信小程序 - canvas 转本地临时文件

wx.canvasToTempFilePath({
  x: 0,
  y: 0,
  width: 350,
  height: 450,
  canvasId: 'myCanvas',
  success: function (res) {
    // 获取到临时文件路径，我们也可以使用这个路径将canvas保存到本地
    let img = res.tempFilePath;
  },
  fail(err) {
    console.log(err);
  },
});

bas64 转 blob 上传

/**
  * 根据base64 内容 取得 bolb
  *
  * @param dataURI
  * @returns Blob
*/
getBlobBydataURI(dataURI, type) {
  var binary = atob(dataURI.split(',')[1]);
  var array = [];
  for (var i = 0; i < binary.length; i++) {
    array.push(binary.charCodeAt(i));
  }
  return new Blob([new Uint8Array(array)], { type: type });
},
/**
  * 上传
*/
base64Upload(base64, url) {
  // base64 转 blob
  var $Blob = this.getBlobBydataURI(base64, 'image/png');
  var formData = new FormData();
  formData.append("file", $Blob, "avatar.png");
  // 组建XMLHttpRequest 上传文件
  var request = new XMLHttpRequest();
  // 上传连接地址
  request.open("POST", url);
  // return new Promise((resolve, reject) => {
  request.onreadystatechange = function () {
    if (request.readyState == 4) {
      if (request.status == 200) {
        console.log("上传成功", request);
      } else {
        console.log("上传失败,检查上传地址是否正确", request);
      }
    }
  }
  // })
  request.send(formData);
}

JS 判断 Base64 图片格式

function getBase64ImageType(base64) {
  var base64Data = base64.split(',')[1];
  var dataBuffer = Buffer.from(base64Data, 'base64');
  var type = fileType(dataBuffer);
  return type ? type.ext : null;
}

但其实上面的方法不对，真正的 png 和 jpg 还是有差异的，这篇文章也说明了原因

• https://stackoverflow.com/questions/49664561/determine-if-a-base64-string-or-a-buffer-contains-jpeg-or-png-without-metadata
• 详述图片 base64 加密的原理，告诉你什么是“/9j/“

我在这篇文章中找到一个比较好的

/**
 * @author PiaoZhenJia
 */
function base64FileHeaderMapper(fileBase64) {
  let fileHeader = new Map();

  //get the first 3 char of base64
  fileHeader.set('/9j', 'JPG');
  fileHeader.set('iVB', 'PNG');
  fileHeader.set('Qk0', 'BMP');
  fileHeader.set('SUk', 'TIFF');
  fileHeader.set('JVB', 'PDF');
  fileHeader.set('UEs', 'OFD');

  let res = '';

  fileHeader.forEach((v, k) => {
    if (k == fileBase64.substr(0, 3)) {
      res = v;
    }
  });

  //if file is not supported
  if (res == '') {
    res = 'unknown file';
  }

  //return map value
  return res;
}

JS 获取图片 EXIF 旋转角度

function getOrientation(file, callback) {
  var reader = new FileReader();
  reader.onload = function (e) {
    var view = new DataView(e.target.result);
    if (view.getUint16(0, false) != 0xffd8) return callback(-2);
    var length = view.byteLength,
      offset = 2;
    while (offset < length) {
      var marker = view.getUint16(offset, false);
      offset += 2;
      if (marker == 0xffe1) {
        if (view.getUint32((offset += 2), false) != 0x45786966) {
          return callback(-1);
        }
        var little = view.getUint16((offset += 6), false) == 0x4949;
        offset += view.getUint32(offset + 4, little);
        var tags = view.getUint16(offset, little);
        offset += 2;
        for (var i = 0; i < tags; i++)
          if (view.getUint16(offset + i * 12, little) == 0x0112)
            return callback(view.getUint16(offset + i * 12 + 8, little));
      } else if ((marker & 0xff00) != 0xff00) break;
      else offset += view.getUint16(offset, false);
    }
    return callback(-1);
  };
  reader.readAsArrayBuffer(file);
}

JS 旋转图片

function 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
  var height = img.height;
  var width = img.width;
  var 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
  var degree = (step * 90 * Math.PI) / 180;
  var 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;
  }
}

base64 to blob url

function dataURLtoBlob(dataurl) {
  var arr = dataurl.split(','),
    mime = arr[0].match(/:(.*?);/)[1],
    bstr = atob(arr[1]),
    n = bstr.length,
    u8arr = new Uint8Array(n);
  while (n--) {
    u8arr[n] = bstr.charCodeAt(n);
  }
  return new Blob([u8arr], { type: mime });
}

另外一种

// first convert to blob
const dataToBlob = async (imageData) => {
  return await (await fetch(imageData)).blob();
};

const blob = await dataToBlob(destination.value);

// then create URL object
const url = URL.createObjectURL(blob);

base64 编码和解码

// base64编码
function base64Encode(str) {
  return btoa(
    encodeURIComponent(str).replace(/%([0-9A-F]{2})/g, function (match, p1) {
      return String.fromCharCode('0x' + p1);
    })
  );
}
// base64解码
function base64Decode(str) {
  return decodeURIComponent(
    atob(str)
      .split('')
      .map(function (c) {
        return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
      })
      .join('')
  );
}

sharp 图片处理

// 使用nodejs裁剪图片并输出
const sharp = require('sharp');
const image = sharp(filename);
const bbox = predictionResultObj.bboxes[i];
const xMin = bbox[0];
const xMax = bbox[1];
const yMin = bbox[2];
const yMax = bbox[3];
// 获取图片的宽高
const metadata = await image.metadata();
const imageWidth = metadata.width;
const imageHeight = metadata.height;
// 计算裁剪的坐标
const left = Math.round(xMin * imageWidth);
const top = Math.round(yMin * imageHeight);
const width = Math.round((xMax - xMin) * imageWidth);
const height = Math.round((yMax - yMin) * imageHeight);
// 裁剪图片
await image
  .extract({ left, top, width, height })
  .toFile(`output/${label}${ids}.jpg`);

后记

• http://www.perry.cz/files/ExifRestorer.js
• https://github.com/gchudnov/inkjet
• 这还有个获取 exif 旋转照片的例子
• https://exiftool.org/TagNames/EXIF.html