calculateInSampleSize
Calculate the largest inSampleSize value that is a power of 2 and keeps both height and width larger than the requested height and width.
Taken from http://developer.android.com/training/displaying-bitmaps/load-bitmap.html.
Return
The calculated inSampleSize.
Parameters
width
The width of the image.
height
The height of the image.
reqWidth
The requested width of the image.
reqHeight
The requested height of the image.