How to convert YUV420 format black and white diagram chart

How to convert image YUV420 format black and white map, or keep YUV format conversion is not converted into RGB, equivalent to only go to YUV420 color. Preferably with java source code segment, novice Thank you.
I use this code, although the format right, but not all black and white, there are variegated, seeking correction

System.arraycopy (data, row * RectWidth, yuvDest, 0, RectWidth * RectHeight);<-! Main posts under Banner (D4) -><-! Posts under the main text (D5) ->
Reply:
Reserved Y component, the other component is set to 0