screenres 320,200
bload "temp.bmp"
palette
for iY as long = 0 to 199
  for iX as long = 0 to 319
    var iC = point(iX,iY)
    if ((iX+iY) and 1) then
      pset(iX,iY),(iC and 15)
    else
      pset(iX,iY),(iC shr 4)
    end if
  next iX
next iY

bsave "temp2.bmp",0

sleep