Here is how you can get a .png screenshot of an OpenGL image on Android:
// GL10 gl;
// int width, height;
int size = width * height;
ByteBuffer buf = ByteBuffer.allocateDirect(size * 4);
buf.order(ByteOrder.nativeOrder());
gl.glReadPixels(0, 0, width, height, GL10.GL_RGBA, GL10.GL_UNSIGNED_BYTE, buf);
int data[] = new int[size];
buf.asIntBuffer().get(data);
buf = null;
Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
bitmap.setPixels(data, size-width, -width, 0, 0, width, height);
data = null;
short [...]