```{r}

# read in geotif as raster
relief <- raster("/Users/zehran/Downloads/srgyhii200l_nt00248/srgyhii200l.tif") %>%
  # convert to data frame
  as("SpatialPixelsDataFrame") %>%
  as.data.frame() %>%
  rename(value = `srgyhii200l`) %>%
  # filter out blues in geotif
  # this reduces the number of rows from 16m to 420k
  filter(value != 255)

ggplot(
  data = relief,
  aes(
    x = x,
    y = y,
    alpha = value
  )
) +
  geom_raster() +
  # the important part I guess is inverting the alpha range here
  # it goes now from high to low
  scale_alpha(range = c(0.4, 0.01), guide = FALSE) +
  theme_void()

# just a quick helper to produce images with the right aspect ratio (square px)
aspect_ratio <- (max(relief$y) - min(relief$y)) / (max(relief$x) - min(relief$x))

# save as png
ggsave(
  "/Users/zehran/Downloads/srgyhii200l_nt00248/new_zealand.png",
  width = 100,
  height = 100 * aspect_ratio,
  units = "mm"
)

```