Base64 encoding product different result - php

Question

I am working on android project which can upload image from user's phone galery. The method i use to upload the image is to encode the image to base64 in android and send it to PHP files on server, then the PHP file decodes it then put it on server.
But the problem is the result of PHP decoding is different with the original image. Although the image is still working, but i am afraid sometimes it's gonna be a bug :D..
How to solve it?
Class UploadImageCatalog
#Override
protected String doInBackground(String... params) {
String urlAPI = params[0];
String id = params[1];
String imageByte = params[2];
try {
URL url = new URL(urlAPI);
HttpURLConnection urlCon = (HttpURLConnection) url.openConnection();
urlCon.setReadTimeout(15000);
urlCon.setConnectTimeout(15000);
urlCon.setDoOutput(true);
urlCon.setRequestMethod("POST");
OutputStream os = urlCon.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os, "UTF-8");
BufferedWriter bw = new BufferedWriter(osw);
String postData = URLEncoder.encode("id", "UTF-8")+"="+URLEncoder.encode(id, "UTF-8")+"&"+
URLEncoder.encode("imageByte", "UTF-8")+"="+URLEncoder.encode(imageByte, "UTF-8");
bw.write(postData);
bw.flush();
bw.close();
osw.close();
os.close();
urlCon.connect();
int responseCode = urlCon.getResponseCode();
if (responseCode == HTTP_OK) {
InputStream is = urlCon.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String responseString = br.readLine();
br.close();
isr.close();
is.close();
return responseString;
}
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
Method getStringImage()
private String getStringImage(Bitmap bmp){
ByteArrayOutputStream baos = new ByteArrayOutputStream();
bmp.compress(Bitmap.CompressFormat.JPEG, 100, baos);
byte[] imageBytes = baos.toByteArray();
return Base64.encodeToString(imageBytes, Base64.DEFAULT);
}
Mehthod to upload image
btSave.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (updateImage) {
new UploadImageCatalog(ViewProductActivity.this)
.execute(SERVER_URL+"/project/katalogmukenalukis/uploadimage.php",
String.valueOf(idToView), getStringImage(imageLoadedBitmap));
} else {
updateData();
}
}
});
uploadimage.php
<?php
$id = $_POST['id'];
$imageByte = $_POST['imageByte'];
$target = __DIR__."/asset/".$id;
if (file_exists($target)) {unlink($target);}
if (file_put_contents($target, base64_decode($imageByte))) {
echo json_encode(array("success" => true));
} else {
echo json_encode(array("success" => false, "message" => ""));
}
?>