text,f,a,,,,Text file description of mask regions
mask,f,a,,,,Mask image name
ncols,i,a,,1,,Number of columns in mask
nlines,i,a,,1,,Number of lines in mask
linterp,i,h,1,1,,Mask code for rectangles narrower along lines
cinterp,i,h,2,1,,Mask code for rectangles narrower along columns
square,i,h,3,1,,Mask code for squares
pixel,i,h,4,1,,Mask code for single pixels