HarmonyOS pixelMap转成ArrayBuffer

下面2个方法的输入都是pixelMap，最后都输出ArrayBuffer，但是输出的arraybuffer好像不一样。想问一下这两个有什么不同？使用场景分别是什么？

const readBuffer = new ArrayBuffer(pixelBytesNumber);
pixelMap.readPixelsToBuffer(readBuffer).then(() => {
  console.info('Succeeded in reading image pixel data.');
}).catch((error : BusinessError) => {
  console.error('Failed to read image pixel data. And the error is: ' + error);
})


import {BusinessError} from '@ohos.base'
imagePackerApi.packing(imageSource, packOpts).then( (data : ArrayBuffer) => {

}).catch((error : BusinessError) => {
  console.error('Failed to pack the image. And the error is: ' + error);
})