wxml文件：
<view>
<!–相机组件–>
<camera device-position=’{{status}}’ model=‘normal’ flash=‘off’ style=‘width:{{w}}px;height:{{h}}px’ binderror=‘error’>

<cover-view style="position:absolute" hidden='{{hideTakeButton}}' bindtap='test'>
    <button type='primary' plain='true'>测试</button> 
</cover-view>

<!--头像框-->
<cover-view style="position:absolute;width:100%;height:{{h}}px;z-index:-99" hidden='{{hideMask}}'>
  <cover-image src='{{config.imgBasePath}}/img/face_mask.png'></cover-image>
</cover-view> 

<!--拍摄按钮-->
<cover-view style="position:absolute;bottom:17%;left:{{(w-66)/2}}px;" hidden='{{hideTakeButton}}' bindtap='takePhoto'>
  <cover-image src='{{config.imgBasePath}}/img/takephoto_take.png'style="width:132rpx;"></cover-image>
</cover-view>

<!--定格图片-->
<cover-view style='position:absolute;width:100%;height:{{h}}px;z-index:-1' hidden='{{hideCoverImage}}'>
  <cover-image src="{{showPath}}"></cover-image>
</cover-view>

<!--重拍按钮-->
<cover-view class="complete" hidden='{{hideCoverButton}}'>
    <button class="reset" bindtap='takeAgain'>重拍</button>
    <button class="submit" bindtap='confirm'>完成</button>
</cover-view>

</camera>
<!-- <view style=“position:fixed;top:999999999999999999999rpx;”>
<canvas style=“width:{{cw}}px;height:{{ch}}px;” canvas-id=‘firstCanvas’>
</canvas>
</view> -->
</view>

js相关：
/**

• 页面的初始数据
  */
  data: {
  filePath: ‘’,
  showPath:’’,
  status: ‘front’,
  w: app.globalData.winWidth,
  h: app.globalData.screenHeight,
  cw: 300,
  ch: 200,
  hideTakeButton: false,
  hideCoverImage: true,
  hideCoverButton: true,
  hideMask:false
  },
  压缩方法：
  //处理页面绑定事件
  takePhoto() {
  let that = this;
  const ctx = wx.createCameraContext()
  ctx.takePhoto({
  quality: ‘high’,
  success: (res) => {
  let tempPath = res.tempImagePath
  that.setData({
  showPath : tempPath
  })
  let zipedPath = ‘’;
  //直接压缩开始
  wx.compressImage({
  src: tempPath,
  quality:60,
  success:function®{
  zipedPath= r.tempFilePath
  //console.log(“压缩后：” + zipedPath);
  that.setData({
  filePath: zipedPath,
  hideTakeButton: true,
  hideMask:true,
  hideCoverButton: false,
  hideCoverImage: false
  })
  }
  })
  //直接压缩结束
  },
  fail: function() {
  wx.showToast({
  title: ‘照片拍摄失败，请检查摄像头’,
  icon: ‘none’
  })
  }
  })
  },

//点击确定才开始上传文件
confirm: function() {
let that = this;
that.setData({
hideCoverButton: true
});
wx.showLoading({
title: ‘图片上传中…’,
mask: true
})

//调用文件处理方法
//that.zipImage();
//上传压缩过的文件
let uploadfilePath = that.data.filePath;
console.log("获取上传图片："+uploadfilePath)
that.uploadzipBase64(uploadfilePath);

},

//重拍按钮
takeAgain: function() {
let that = this;
that.setData({
hideTakeButton: false,
hideMask:false,
hideCoverImage: true,
hideCoverButton: true,
filePath: ‘’
});
},

//图片压缩后直接上传BASE64格式
zipImage: function() {
let that = this;
let filePath = that.data.filePath;
var uploadFile = ‘’;
//文件压缩
//获得原始图片大小
wx.getImageInfo({
src: filePath,
success(res) {
var originWidth = res.width;
var originHeight = res.height;
console.log(“原始宽高比” + originWidth + “:” + originHeight);
//设置压缩比例,最大尺寸限度
var maxWidth = 1200;
var maxHeight = 600;
//目标尺寸
var targetWidth = originWidth;
var targetHeight = originHeight;
//等比例压缩，如果宽度大于高度，则宽度优先，否则高度优先
if (originWidth > maxWidth || originHeight > maxHeight) {
if (originWidth / originHeight > maxWidth / maxHeight) {
//宽度*原生图片比例=新图片尺寸
targetWidth = maxWidth;
targetHeight = Math.round(maxWidth * (originHeight / originWidth));
} else {
targetHeight = maxHeight;
targetWidth = Math.round(maxHeight * (originWidth / originHeight));
}
}
//尝试压缩文件，创建canvas
var ctx = wx.createCanvasContext(‘firstCanvas’);
ctx.clearRect(0, 0, targetWidth, targetHeight);
ctx.drawImage(filePath, 0, 0, targetWidth, targetHeight);
//canvas压缩后图片处理要写在draw方法的回调里
ctx.draw(false, function callback() {

      //更新canvas大小
      that.setData({
        cw: targetWidth,
        ch: targetHeight
      });
      //保存图片
      setTimeout(function() {
        wx.canvasToTempFilePath({
          canvasId: 'firstCanvas',
          fileType: 'jpg',
          success: (res) => {
            uploadFile = res.tempFilePath;
            //上传
            that.uploadzipBase64(uploadFile);
          }
        }, this)
      }, 500);

    });

  },
  fail() {
    wx.showToast({
      title: '获取图片失败',
      icon: 'none'
    })
  }
})

},

//转BASE64并上传
uploadzipBase64(uploadFile) {
let that = this;
//通过文件系统管理器重新编码文件
const fs = wx.getFileSystemManager();
fs.readFile({
filePath: uploadFile,
encoding: “base64”,
success: function(res) {
var base64Data = res.data;
console.log(“开始上传”)
//调用你的ajax请求上传后台
ajaxUpload();
},
fail: function() {
wx.showToast({
title: ‘读取图片失败’,
icon: ‘none’
})
}
});

},

//绑定出错事件
error(e) {
wx.showToast({
title: ‘照片拍摄失败，请检查摄像头’,
icon: ‘none’
})
}
总结：
以上示例，图片压缩可以通过2种方式：
1.官方的api：wx.compressImage({}）
2.利用canvas进行压缩重绘
转化为BASE64编码方式：通过文件系统管理器，读文件转化
const fs = wx.getFileSystemManager();