convert Y component to image

Hi

I need your help please. I want to take a video retrieve the Y component, and create images from it.

I have download the yuv_import function I can retrieve 2 frames of the Y component with the following command

[Y, U, V] = yuv_import('foreman_qcif.yuv',[176 144],2);

and now i want to convert this 2 frames of the Y component to images why cant I use the following command ?

*img=imread(Y{1}) *

what can I do in order to convert it ?

Thanks