getRow
Fetches one row of luminance data from the underlying platform's bitmap. Values range from 0 (black) to 255 (white). Because Java does not have an unsigned byte type, callers will have to bitwise and with 0xff for each value. It is preferable for implementations of this method to only fetch this row rather than the whole image, since no 2D Readers may be installed and getMatrix() may never be called.
Return
An array containing the luminance data.
Parameters
y
The row to fetch, which must be in [0,getHeight())
row
An optional preallocated array. If null or too small, it will be ignored. Always use the returned object, and ignore the .length of the array.