Converting an image to a bitmap
A couple of thoughts.


Always think about breaking your code into discrete units of work, this will make it more logical, more readable and importantly, more testable. In your case, separate out the reading of the data from the creation of the bitmap.
The ambiguous return will either be because you are modifying multiple local properties (count, len, buffer) or because you return a new Bitmap or null from different points in your code. By needing to use count in your Bitmap creation you make it harder to refactor.
If you are concerned about 0 length returns from inputStream.read() consider adding a handbrake to avoid infinite loops - I have never encountered this in real life  though.
Does your code perform better than using ByteArrayOutputStream, something like the below.


Code:

//add throws or try/catch as suits your code.

private byte[] readBitmapData() {
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    byte[] inputBuffer = new byte[16384]; //16K default buffer size
    int nRead;

    while ((nRead = is.read(inputBuffer, 0, data.length)) != -1) {
        buffer.write(inputBuffer, 0, nRead);
    }

    return buffer.toByteArray();
}


You can check out the OpenJDK code for ByteArrayOutputStream on docjar. Note their code for grow and ensureCapacity.