library(png)
none <- png::readPNG("Figures/params-anti-alias-none.png")
gray <- png::readPNG("Figures/params-anti-alias-gray.png")
sub <- png::readPNG("Figures/params-anti-alias-subpixel.png")

  ## Tweak 'gray', which was generated in Linux to match 
  ## others which were generated on Windows
gray2 <- as.raster(rbind("#FFFFFF", 
                         cbind(matrix(as.raster(gray), 
                                      c(25, 50), byrow=TRUE)[, -1], 
                               "#FFFFFF")[-25, ]))
pushViewport(viewport(x=1/6, width=1/3, clip=TRUE))
grid.raster(none, width=3/2, interpolate=FALSE)
popViewport()
pushViewport(viewport(x=3/6, width=1/3, clip=TRUE))
grid.raster(gray2, width=3/2, interpolate=FALSE)
popViewport()
pushViewport(viewport(x=5/6, width=1/3, clip=TRUE))
grid.raster(sub, width=3/2, interpolate=FALSE)
popViewport()