Memory limitations

[A-KL]

Hi,
I'm working on a simple app that communicates (sends POST requests) to a remote server in order to apply complex image effects. At the moment, APIs require an image to be base64 encoded and sent as a part of a JSON payload.

Everything works perfectly in emulator but on a real device - I get OutOfMemoryError. The code is pretty simple and seems to consume around 20mb (I did a few tests using the same emulator).

File image = new File("/mnt/sdcard/DCIM/" + info.getFolder() + "/" + info.getFilename());
FileInputStream inputStream = new FileInputStream(image);
int size = inputStream.available();
byte[] buffer = new byte[size]; // 4MB
inputStream.read(buffer);
inputStream.close();

String base64Data = Base64.encodeToString(buffer, 0, buffer.length, Base64.DEFAULT); // 15MB

Stack trace from a device (Sony A6000) :

[ERROR] java.lang.RuntimeException: An error occured while executing doInBackground()
java.lang.RuntimeException: An error occured while executing doInBackground()
	at android.os.AsyncTask$3.done(AsyncTask.java:200)
	at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
	at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
	at java.util.concurrent.FutureTask.run(FutureTask.java:138)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
	at java.lang.Thread.run(Thread.java:1019)
Caused by: java.lang.OutOfMemoryError
	at android.util.Base64.encode(Base64.java:534)
	at android.util.Base64.encodeToString(Base64.java:477)
	at com.github.ma1co.pmcademo.app.ImageAsyncTask.doInBackground(ImageAsyncTask.java:42)
	at com.github.ma1co.pmcademo.app.ImageAsyncTask.doInBackground(ImageAsyncTask.java:13)
	at android.os.AsyncTask$2.call(AsyncTask.java:185)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
	... 4 more

The system itself seems to have around 82Mb of RAM available, so what could cause the issue? I'm pretty new to a mobile developent, but does Android has a limitation per activity\background task?

I'm using Android 4.04 for the emulator.