Need help on understanding "convertBitmapToByteBuffer" and "applyfilter"

[MiceXH]

I dontt understand how these operating can convert Bitmap to ByteBuffer.
imgData.putFloat((((val >> 16) & 0xFF)-IMAGE_MEAN)/IMAGE_STD); imgData.putFloat((((val >> 8) & 0xFF)-IMAGE_MEAN)/IMAGE_STD); imgData.putFloat((((val) & 0xFF)-IMAGE_MEAN)/IMAGE_STD);
I also have problem on understanding how low pass filter works.
Details needed.
Thanks!