HarmonyOS 如何将图片压缩并转成base64

可以参考下面demo：

import photoAccessHelper from '@ohos.file.photoAccessHelper';
import image from '@ohos.multimedia.image';
import fs from '@ohos.file.fs';
import { buffer } from '@kit.ArkTS';

@Entry
@Component
struct Page2 {
  @State resultBase64Str: string = '';
  @State getAlbum: string = '显示相册中的图片';
  @State pixel: image.PixelMap | undefined = undefined;
  @State albumPath: string = '';
  @State photoSize: number = 0;


  async getPictureFromAlbum() {
    // 拉起相册，选择图片
    let PhotoSelectOptions = new photoAccessHelper.PhotoSelectOptions();
    PhotoSelectOptions.MIMEType = photoAccessHelper.PhotoViewMIMETypes.IMAGE_TYPE;
    PhotoSelectOptions.maxSelectNumber = 1;
    let photoPicker = new photoAccessHelper.PhotoViewPicker();
    let photoSelectResult: photoAccessHelper.PhotoSelectResult = await photoPicker.select(PhotoSelectOptions);
    this.albumPath = photoSelectResult.photoUris[0];
    console.info('albumPath: ' + this.albumPath)
    // 读取图片为buffer
    const file = fs.openSync(this.albumPath, fs.OpenMode.READ_WRITE);
    this.photoSize = fs.statSync(file.fd).size;
    console.info('Photo Size: ' + this.photoSize);
    let buffer1 = new ArrayBuffer(this.photoSize);
    fs.readSync(file.fd, buffer1);
    let base64Str: string = buffer.from(buffer1).toString('base64')
    let resultBase64Str = "data:image/png;base64," + base64Str
    this.resultBase64Str = resultBase64Str
    fs.closeSync(file);
    // 解码成PixelMap
    const imageSource = image.createImageSource(buffer1);
    console.log('imageSource: ' + JSON.stringify(imageSource));
    this.pixel = await imageSource.createPixelMap({});
  }

  build() {
    Scroll() {
      Column() {
        Text('获取图片')
          .onClick(async () => {
            await this.getPictureFromAlbum()
          })
        // Image(this.pixel)
        Image(this.resultBase64Str).width(40).height(40)

        Text(this.resultBase64Str)
      }
    }
  }
}

图片打包和压缩，可以参考我们ImagePacker中的packing接口，参考链接：https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/js-apis-image-V5#imagepacker，打包压缩之后返回的arraybuffer数据就可以使用之前提供代码里边的buffer.from(buffer1).toString(‘base64’)代码去转base64