png/svg/pdf read by magick

png/svg/pdf images read by magick package, and the resultant format

Published

April 29, 2026

R包magick用三个读取图片的函数，分别是image_read()、image_read_svg()、和image_read_pdf()。

因此测试下其将图片读取后的图片格式是什么。

1. 下载png和svg图片

从https://bioart.niaid.nih.gov/bioart/668下载png格式（位图图像）和svg格式（矢量图）。

"images/" |> 
  fs::dir_tree(regexp = "^images/Rabbit0001\\.(png|svg)")  
images/
├── Rabbit0001.png
└── Rabbit0001.svg

2. 将svg图片转为pdf格式

图片用microsoft edge浏览器打开svg图片 → 打印为microsoft pdf。

"images/" |> 
  fs::dir_tree(regexp = "^images/rabbit")  
images/
└── rabbit0001.pdf

3. 读取图片

3.1 读取png格式

magick |> library()
Linking to ImageMagick 6.9.13.29
Enabled features: cairo, freetype, fftw, ghostscript, heic, lcms, pango, raw, rsvg, webp
Disabled features: fontconfig, x11
png <- "images/Rabbit0001.png" |> 
  magick::image_read()

png |> image_info()
  format width height colorspace matte filesize density
1    PNG  2084   2084       sRGB  TRUE   205821 118x118
png |> plot()

读取为png格式。

3.2 读取svg格式

svg <- "images/Rabbit0001.svg" |> 
  magick::image_read_svg()

svg |> image_info()
  format width height colorspace matte filesize density
1    PNG   500    500       sRGB  TRUE        0   72x72

读取为png格式。

3.3 读取pdf格式

pdf <- "images/rabbit0001.pdf" |> 
  magick::image_read_pdf()

pdf |> image_info()
  format width height colorspace matte filesize density
1    PNG  2481   3508       sRGB  TRUE        0 300x300

读取为png格式。

4. 用image_read()读取svg和pdf

# read svg
svg1 <- "images/Rabbit0001.svg" |> 
  magick::image_read()

svg1 |> image_info()
  format width height colorspace matte filesize density
1    SVG   500    500       sRGB  TRUE    49183   96x96
svg1 |> plot()

读取为svg格式（image_read()无法读取pdf）。

5. image_read读取的svg是否可以嵌入tidyplots？

tidyplots |> library()

# View image information
img_info <- svg1 |> magick::image_info()
img_width <- img_info$width; img_height <- img_info$height
# Change to graphical object
img_grob <- svg1 |> grid::rasterGrob()

# Create a data frame relevant to img_grob
df <- tibble::tibble(x = seq(0, img_width, length.out = 100),
  y = seq(0, img_height, length.out = 100))

# The intended width of image
img_intend_width = 50 # unit: mm
# Tailor relative extra spaces of plot
top_extra = 0 # 0 (0%) - 1 (100%)
right_extra = 0; bottom_extra = 0; left_extra = 0

# The width and height of plot
plot_width = img_intend_width * (1 + left_extra + right_extra) # unit: mm
plot_height = img_intend_width * (img_height/img_width) * (1 + top_extra + bottom_extra)

# Plot
p1 <- df |> tidyplot(x = x, y = y) |> 
  add_data_points(alpha = 0) |> 
  add(ggplot2::annotation_custom(img_grob, xmin = 0, xmax = img_width, 
    ymin = img_height, ymax = 0))

p1

p1 |> 
  save_plot("images/Rabbit0001_tidyplot.pdf", view_plot = FALSE) |> 
  save_plot("images/Rabbit0001_tidyplot.png", view_plot = FALSE)
✔ save_plot: saved to 'images/Rabbit0001_tidyplot.pdf'
✔ save_plot: saved to 'images/Rabbit0001_tidyplot.png'