converting YCbCr 4:4:4 to 4:2:0

hi

I'm trying to convert RGB to YCbCr 4:2:0,but when I insert this code to mathlab==>

 ycbcrimage=rgb2ycbcr(RGB image)

in this case this code gives me 4:4:4 mode,but I want 4:2:0.

how can i get this?

thank you in advance for what you are trying to do for me.

good luck

[Walter Roberson]

http://www.mathworks.com/matlabcentral/fileexchange/40486