Rotate an image with transparent background

Question

I have trouble rotating images with transparent background while retaining a transparent background. magick::image_rotate() adds a white background with a gray border (I think due to anti-aliasing).

How do I rotate an image in R while retaining a transparent background?

I want to use the rotated image in annotation_custom() to overlay on an existing ggplot.

Here is a reproducible example with my tries so far, that demonstrates my problems:

library("magick")

## read R-logo
rlogo <- image_read("https://www.r-project.org/logo/Rlogo.png")
plot(as.raster(rlogo))

## transparent background
rlogo <- image_transparent(rlogo, color = "white")
plot(as.raster(rlogo))

## rotate
rlogo <- image_rotate(rlogo, degrees = 45)
plot(as.raster(rlogo))

## black canvas
canvas <- image_blank(
    width  = image_info(rlogo)$width,
    height = image_info(rlogo)$height,
    color  = "black")
plot(as.raster(canvas))

## 1st try: rotated R logo on black canvas
rlogo_blackbg <- image_composite(canvas, rlogo, operator = "over")
plot(as.raster(rlogo_blackbg))
## -> image_rotate added white background
##    (white corners!)

## try to fix: transparent background again
rlogo <- image_transparent(rlogo, color = "white")
plot(as.raster(rlogo))

## 2nd try: rotated R logo on black canvas
rlogo_blackbg <- image_composite(canvas, rlogo, operator = "over")
plot(as.raster(rlogo_blackbg))
## -> the anti-aliasing during image_rotate created border
##    (frame around the rotated image)

It is really hard to follow the code as you're overwriting rlogo multiple times. Please use different names for each step. — M--
– M--, Commented Aug 17 at 9:05

M-- · Accepted Answer · 2025-08-17 09:13:21Z

4

Make the background transparent using magick::image_background():

library("magick")
#> Linking to ImageMagick 6.9.12.98
#> Enabled features: cairo, freetype, fftw, 
#> ghostscript, heic, lcms, pango, raw, rsvg, webp
#> Disabled features: fontconfig, x11

rlogo <- image_read("https://www.r-project.org/logo/Rlogo.png")

rlogo_rt <- rlogo |>
  image_background("transparent") |>
  image_rotate(degrees = 45) 

canvas <- image_blank(
  width  = image_info(rlogo_rt)$width,
  height = image_info(rlogo_rt)$height,
  color  = "black")

rlogo_blackbg <- image_composite(canvas, rlogo_rt, operator = "over")

plot(as.raster(rlogo_blackbg))

^{Created on 2025-08-17 with reprex v2.1.1}

answered Aug 17 at 9:13

M--

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