const ctx = wx.createCanvasContext('CanvasId');       console.log(this.data.front)//图片临时地址       wx.getImageInfo({             src: this.data.front,             success: (res) => {                   var ratio = this.data.pixelRatio                   if (res.width > size) { // 判断图片是否超过300像素                         // var scale = res.height / res.width                         this.setData({                               cWidth:Math.trunc(res.width / ratio),                               cHeight:Math.trunc(res.height / ratio)                         })                         // 画出压缩图片                         ctx.drawImage(this.data.front, 0, 0, this.data.cWidth, this.data.cHeight);                         ctx.draw(false,                                                                   setTimeout(() => {                                     wx.canvasToTempFilePath({                                           canvasId: 'CanvasId',                                           fileType: 'jpg',                                           quality:1,                                           success: (res) => {                                                 console.log(res.tempFilePath)                                                                                            },                                           fail: (res) => {                                                 console.log(res)                                           }                                     })                               },300)                                                                                 )                                }       }); 压缩的图片比原来的图片还大，不知道怎么回事