如何实现PixelMap和base64的相互转换

let resourceManager = getContext(this).resourceManager 
let imageArray = await resourceManager.getMediaContent($r('app.media.beer')); 
let pixelBuffer = new Uint8Array(imageArray).buffer as Object as ArrayBuffer 
let imageResource = image.createImageSource(pixelBuffer); 
let opts: image.DecodingOptions = { editable: true } 
let pixelMap = await imageResource.createPixelMap(opts); 
  
// 转换成base64 
const imagePackerApi: image.ImagePacker = image.createImagePacker(); 
let packOpts: image.PackingOption = { format: 'image/jpeg', quality: 100 }; 
imagePackerApi.packing(pixelMap, packOpts).then((data: ArrayBuffer) => { 
  let buf: buffer.Buffer = buffer.from(data); 
  this.base64 = 'data:image/jpeg;base64,' + buf.toString('base64', 0, buf.length); 
  console.info('base64: ' + this.base64); 
})

import util from '@ohos.util'; 
  
let helper = new util.Base64Helper(); 
// 传入的base64字符串内容为：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 
let buffer: ArrayBuffer = helper.decodeSync(this.base64, util.Type.MIME).buffer as ArrayBuffer; 
let imageSource = image.createImageSource(buffer); 
let opts: image.DecodingOptions = { editable: true }; 
this.pixelMap = await imageSource.createPixelMap(opts);