set.seed(1)
i <- j <- 200
m <- matrix(runif(i*j), i, j)

library(pixmap)
fmaker <- function() tempfile(fileext = ".pnm")

## pixmap
## I cannot get this to work
fpix <- function(x, write = TRUE) {
  suppressWarnings(out <- pixmap::pixmap(x))
  if (write) pixmap::write.pnm(out, fmaker())
  out
}

## raster (uses rgdal for the write)
fras <- function(x, write = TRUE) {
  out <- raster::raster(x)
  if (write) raster::writeRaster(out, fmaker(), format = "PNM")
  out
}
## stars/sf - faster than rgdal
## but can't get this to work with Float32 type
fstr <- function(x,write = TRUE) {
  out <- stars::st_as_stars(x)
  if (write) sf::gdal_write(out, file = fmaker(), driver = "PNM",
                            geotransform = c(0, 1, 0, nrow(x), 0, -1), type = "Byte")
  out
}
rbenchmark::benchmark(raster = fras(m), stars = fstr(m))

##     test replications elapsed relative user.self sys.self user.child
## 1 raster          100   3.279    10.12     3.058    0.218          0
## 2  stars          100   0.324     1.00     0.263    0.062          0
##   sys.child
## 1         0
## 2         0