pixmap question again

I could load a picture with gray levels only:

x <- 
read.pnm("/home/christoph/work/projects/ffa/EPrime/pics_pnm/550_0_1.pnm")

x

Pixmap image
  Type          : pixmapGrey
  Size          : 246x192
  Resolution    : 1x1
  Bounding box  : 0 0 192 246

plot(x)

works fine

BUT: how can I get to the slots as "size", "grey", etc.
 
calling:

x$grey

NULL

x$size

NULL

why this?

I need to get the grey value of each pixel and average all grey values
over the whole picture... 

thanks

christoph

Christoph Lehmann <lehmann at puk.unibe.ch>
University Hospital of Clinical Psychiatry