Show Image from s3Bucket to html page

We are trying to display an image which exist in amazon s3 bucket in angular8. Our code is:-
In HTML:-

In ts:-

DownloadFromS3(FilePath, FileName) {
// Set up credentials
let AWSS3AccessKey = environment.AWSS3AccessKey
let AWSS3SecretKey = environment.AWSS3SecretKey
let S3Bucketname = environment.S3Bucketname
let S3BucketRootFolder = environment.S3BucketRootFolder

AWS.config.credentials = new AWS.Credentials({
  accessKeyId: AWSS3AccessKey, secretAccessKey: AWSS3SecretKey
});

const params = {
  Bucket: S3Bucketname,
  Key: S3BucketRootFolder + FilePath + "/" + FileName

};

let s3 = new AWS.S3();

let base64String = "";

s3.getObject(params, function (err, data) {//unit8array
if (err) {
console.error(err); // an error occurred
}
else
{
//downloading the file inclient machine
const STRING_CHAR = String.fromCharCode.apply(null, data.Body);
base64String = btoa(STRING_CHAR);
return base64String;

  }
});

}
//Calling Method
val= this.DownloadFromS3(this.imagePath, UploadedFileInfo[0].FileName);

But in s3.getObject function, "this" operator is not working like this.thumbnail is not defined here.

variable val is containing null even the following statement
return base64String;
containing the value.