NodeJs : retrieving image from sfdc rest api and writing file on local system

Question

I am trying to fetch images using SFDC rest API where I can see different types of responses for corresponding javascript file and image. Image retrieved shows a message of "Not supported format" but my javascript file works fine.

These are some screenshots of the responses :

for Image

for Js file

Following is my node JS code for retrieving the attachments from knowledge articles:

function createFile(attachmentBody, attachmntContentType, attachmntName) {
var req = {
 url: attachmentBody,
 method: 'GET',
 headers: {
  "Content-Type": attachmntContentType
 }
};

var test = conn.request(req, function (err, resp) {
  if (err) {
   console.log(err)
  } else {

   var fileBuffer = Buffer.from(resp, 'binary').toString('base64');
   fs.writeFile(attachmntName, fileBuffer, {
    encoding: 'base64'
   }, function (err) {
    if (err)
     throw err
     console.log('File saved.')
   })
  }
 });
}

Please help me with this.