function getImageData64(data) {
        var imageData = data;
        var mimeType = "image/png";
        return NSString.stringWithFormat(
          "data:%@;base64,%@",
          mimeType,
          imageData.base64EncodedStringWithOptions(0)
        );
      }
function getNSImageData(nsImage) {
        var data = nsImage
        var cgRef = nsImage.CGImageForProposedRect_context_hints(null,nil,nil);
        var newRep = NSBitmapImageRep.alloc().initWithCGImage(cgRef);
        newRep.setSize(nsImage.size());   // if you want the same resolution
        var pngData = newRep.representationUsingType_properties(NSPNGFileType,nil);
        return getImageData64(pngData)
}