How to convert RGB to ycbcr420?

I'm trying to convert RGB to ycbcr420. but I don't know how to do that,

if one bmp image is converted to ycbcr,I try to this code,

ycbcrimage=rgb2ycbcr(RGBimage);

but this ycbcrimage is 4:4:4 mode, isn't it?

What can I do to get ycbcr420?

thanks!

Answer 1

[Ben Mitch]

http://www.mathworks.com/matlabcentral/newsreader/view_thread/161961