HarmonyOS 关于图片裁切问题

请参考以下示例：

setPhotoOutputCb(photoOutput: camera.PhotoOutput) {
  //设置回调之后，调用photoOutput的capture方法，就会将拍照的buffer回传到回调中
  photoOutput.on('photoAvailable', (errCode: BusinessError, photo: camera.Photo): void => {
    console.info(`CameraDemo getPhoto start. err: ${JSON.stringify(errCode)}`);
    if (errCode || photo === undefined || photo.main === undefined) {
      console.error('CameraDemo getPhoto failed');
      return;
    }
    let imageObj = photo.main;
    imageObj.getComponent(image.ComponentType.JPEG, async (errCode: BusinessError, component: image.Component): Promise<void> => {
      console.info('CameraDemo getComponent start');
      if (errCode || component === undefined) {
        console.error('CameraDemo getComponent failed');
        return;
      }
      let buffer: ArrayBuffer;
      if (component.byteBuffer) {
        buffer = component.byteBuffer;
        this.buffer = buffer;
        //创建imageSource
        const imageSource = image.createImageSource(buffer)
        //创建PixelMap
        this.finalPixelMap = await imageSource.createPixelMap()
        await this.finalPixelMap.getImageInfo().then((imageInfo: image.ImageInfo) => {
          if (imageInfo == undefined) {
            console.error("Failed to obtain the image pixel map information.");
          } else {
            console.info(`裁剪前information:${JSON.stringify(imageInfo)}`);
          }
        })
        let region: image.Region = { x: 0, y: 0, size: { height: 500, width: 500 } };
        this.finalPixelMap.crop(region).then(async () => {
          console.info('Sucessed in setting crop.');
          if (this.finalPixelMap != undefined) {
            await this.finalPixelMap.getImageInfo().then((imageInfo: image.ImageInfo) => {
              if (imageInfo == undefined) {
                console.error("Failed to obtain the image pixel map information.");
              } else {
                console.info(`裁剪后information:${JSON.stringify(imageInfo)}`);
              }
            })
          }
        }).catch((err: BusinessError) => {
          console.error('Failed to crop pixelmap.');
        })
      } else {
        console.error('CameraDemo byteBuffer is null');
        return;
      }
    });
  });
}

// PixelMap转Buffer
async packingPixelMap2Jpg(pixelMap: PixelMap): Promise<ArrayBuffer> {
  // 创建ImagePacker实例
  const imagePackerApi = image.createImagePacker();
  // 设置打包参数
  // format：图片打包格式，只支持 jpg 和 webp
  // quality：JPEG 编码输出图片质量
  // bufferSize：图片大小，默认 10M
  const packOpts: image.PackingOption = { format: "image/jpeg", quality: 100 };
  let imageBuffer: ArrayBuffer = new ArrayBuffer(1);
  try {
  // 图片压缩或重新打包
  imageBuffer = await imagePackerApi.packing(pixelMap, packOpts);
} catch (err) {
  console.error(`Invoke packingPixelMap2Jpg failed, err: ${JSON.stringify(err)}`);
}
return imageBuffer;
}

//保存至相册
async imageWriteAlbumExample2(pixelMap:image.PixelMap) {
  let imagePackerApi = image.createImagePacker();
  let packOpts: image.PackingOption = { format: "image/jpeg", quality: 98 };
  imagePackerApi.packing(pixelMap, packOpts).then(async (buffer: ArrayBuffer) => {
    try {
      const context = getContext(this)
      let helper = photoAccessHelper.getPhotoAccessHelper(context)
      let uri = await helper.createAsset(photoAccessHelper.PhotoType.IMAGE, 'png')
      let file = await fs.open(uri, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE)
      // 写入文件 注意加一个packing的过程
      await fs.write(file.fd, buffer);
      // 关闭文件
      await fs.close(file.fd);
      promptAction.showToast({
        message: '已保存至相册',
        duration: 2500
      });
    } catch (error) {
      console.error("error is " + JSON.stringify(error))
    }
  }).catch((error: BusinessError) => {
    console.error('Failed to pack the image. And the error is: ' + error);
  })
}