title: Android onPreviewFrame
body: <p>i'm trying to get data from onPreviewFrame(byte[] data, Camera camera)
  and convert it to BASE64,</p>
  
  <p>Base64.encodeToString(data, Base64.DEFAULT)</p>
  
  <p>the result given is not convertible to an image
  (using some sites like <a href="http://codebeautify.org/base64-to-image-converter" rel="nofollow">http://codebeautify.org/base64-to-image-converter</a>)</p>
  
  <p>note that data is a signed byte array that contain some negative values (values between -128 to 127), i think it should be array of unsigned byte, no?</p>
  
  <p>can you help me please, how to get a BASE64 from onPreviewFrame?</p>
  
  <p>thanks,</p>