Question

How do you transform a Bitmap into an InputStream?

I would like to use this InputStream as input to the ETC1Util.loadTexture() function.

Answer 1

This might work

ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
bitmap.compress(CompressFormat.PNG, 0 /*ignored for PNG*/, bos); 
byte[] bitmapdata = bos.toByteArray();
ByteArrayInputStream bs = new ByteArrayInputStream(bitmapdata);