OpenVX read NV21 image raw data into vx_image type

Question

I am learning programming using openVX API's and was trying to create a simple application as follows

read nv21 raw data from disk --> use openVX color convert node to convert from nv21 to rgb --> read back rgb and dump.

Consider following sample code

unsigned char * inputNV21 = (unsigned char*)malloc(((imgW*imgH*3)>>1)*sizeof(unsigned char));
FILE *fp = fopen("lena.yuv", "rb");
fread(inputNV21, ((imgW*imgH*3)>>1), 1, fp));
fclose(fp);

vx_context contextVX = vxCreateContext();
vx_image imageVXNV21 = vxCreateImage(contextVX, imgW, imgH, VX_DF_IMAGE_NV21);

now I am not able to figure out how to put the raw data I have in inputNV21 into imageVXNV21

I have read various openVX sample codes and writing to a rgb vx_image is clear but I am not able to figure out how to deal with the VU channel of NV21 image.