Creates an array of nrow by ncol rectangles.
imageGrob(nrow, ncol, cols, byrow=TRUE,
          name=NULL, gp=NULL, vp=NULL)Number of rows/columns in the image.
Colors for the cells of the image (will be recycled).
Logical value indicating whether colors should be allocated to cells across rows or down columns.
A character name for the grob.
A gpar object containing graphical parameter settings
    or NULL.
A viewport or NULL.