Closed
Description
annotation_raster can be quite slow to display a large image. The current implementation converts the numeric image to text (via grDevices::as.raster) which must be converted back to numeric values for actual drawing by grid::rasterGrob. Supporting nativeRaster removes this round-trip conversion and dramatically speeds rendering.
This reprex uses a modified annotation_raster_native to demonstrate the improvement. A ggplot2 implementation could simply skip the as.raster call in annotation_raster if the incoming raster object inherits from nativeRaster. No changes are needed in GeomRasterAnn because grid::rasterGrob, which it uses, works with nativeRaster objects.
library(ggplot2)
# Image from https://github.com/akoyabio/phenoptrExamples/blob/master/inst/extdata/samples/Set12_20-6plex_%5B14146%2C53503%5D_composite_image.jpg
path = "Set12_20-6plex_[14146,53503]_composite_image.jpg"
image = jpeg::readJPEG(path)
dim(image) # 1400 x 1868
# This takes about 4 seconds to display the plot in RStudio on my computer
print(ggplot() + annotation_raster(image,
xmin=0, xmax=1,
ymin=0, ymax=1))
image2 = jpeg::readJPEG(path, native=TRUE)
# annotation_raster without the grDevices::as.raster conversion
annotation_raster_native <- function(raster, xmin, xmax, ymin, ymax,
interpolate = FALSE) {
layer(
data = ggplot2:::dummy_data(),
mapping = NULL,
stat = StatIdentity,
position = PositionIdentity,
geom = GeomRasterAnn,
inherit.aes = FALSE,
params = list(
raster = raster,
xmin = xmin,
xmax = xmax,
ymin = ymin,
ymax = ymax,
interpolate = interpolate
)
)
}
# This version takes less than two seconds to display.
print(ggplot() + annotation_raster_native(image2,
xmin=0, xmax=1,
ymin=0, ymax=1))