Create multi-panel figure using PNG/JPEG images

Question

Problem:

I want to make a multi-panel figure using PNG or JPEG images. The images were not created in R but I want to patch them together in R to form one figure. All the images are the same size/dimensions.

What I've tried:

library(png)

img1 <- readPNG("filepath/img1.png")
img2 <- readPNG("filepath/img2.png")

library(patchwork)

patch <- img1 + img2
patch

When I run this, I get the following error:

[ reached getOption("max.print") -- omitted 3 matrix slice(s) ]

I increased the max print multiple times (to ridiculously high numbers):

options(maxprint = 1000000000000)

But still get the same error.

I then tried making each image into a ggplot (without the points) using:

library(ggplot2)

img1plot <- ggplot() + 
background_image(img1) +
theme(plot.margin = margin(t=1, l=1, r=1, b=1, unit = "cm"))

Which returns the following error:

Error in background_image(d311) : 
  could not find function "background_image"

Is there another way to patch images together in R to make a figure?

Edit:

Based on the comment from @davidnortes, I tried the following:

p1 <- ggplot2::annotation_custom(grid::rasterGrob(img1,
                                            width=ggplot2::unit(1,"npc"),
                                            height=ggplot2::unit(1,"npc")),
                           -Inf, Inf, -Inf, Inf)

p2 <- ggplot2::annotation_custom(grid::rasterGrob(img2,
                                                  width=ggplot2::unit(1,"npc"),
                                                  height=ggplot2::unit(1,"npc")),
                               -Inf, Inf, -Inf, Inf)


library(cowplot)

plots <- plot_grid(
  p1, p2,
  labels = c('A', 'B'),
  align="hv"
)
plots

I get the following warning messages and the plot doesn't form:

Warning messages:
1: In as_grob.default(plot) :
  Cannot convert object of class LayerInstanceLayerggprotogg into a grob.
2: In as_grob.default(plot) :
  Cannot convert object of class LayerInstanceLayerggprotogg into a grob.

Answer 1

I'm giving you the couple of alternatives that I Use the most:

Alternative 1: combination of ggplot2, grid and cowplot.

Each of your PNG image can be embedded in a ggplot object using:

ggplot2::ggplot() + ggplot2::annotation_custom(grid::rasterGrob(YourPNGimage,
                                                width=ggplot2::unit(1,"npc"),
                                                height=ggplot2::unit(1,"npc")),
                               -Inf, Inf, -Inf, Inf)

Then you can use cowplot::plot_grid() to arrange your plots.

Alternative 2: using magick package.

The package counts on its own functions to read images, thus we need to tweak your code a bit:

img1 <- magick::image_read("filepath/img1.png")
img2 <- magick::image_read("filepath/img2.png")

Then using functions like magick::image_append(c(img1, img2)) you can combine them. See the magick package documentation for more info.