Image Size Reduced when Base64Encoded Image is embedded in rich email containing html

I am working on code to generate rich text html as mail content as eml file.

I have followed below link:

https://jsfiddle.net/seanodotcom/yd1n8Lfh/

The JsFiddler to replicate this issue is : https://jsfiddle.net/AnitaSS/g7jnvuab/1

Code:

<script>
(function () {
debugger

var textFile = null,
  makeTextFile = function (text) {
  debugger
    var data = new Blob([text], {type: 'text/plain'});
    if (textFile !== null) {
      window.URL.revokeObjectURL(textFile);
    }
    if (window.navigator && window.navigator.msSaveOrOpenBlob) {
    window.navigator.msSaveBlob(data, 'message.eml');
    } else {
    textFile = window.URL.createObjectURL(data);
    var link = document.getElementById('downloadlink');
    link.href = textFile;
    link.click();   
    }   
  };

  var create = document.getElementById('create'),
    textbox = document.getElementById('textbox');
  create.addEventListener('click', function () {
     makeTextFile(textbox.value);
  }, false);
})();
</script>

So far my html does render and eml file is downloaded.

However, issue is that I have a base 64 encoded image in my html which get reduced in size when eml file is generated.

Below is screen shot of eml file and html.

Please suggest any inputs to fix this.