Create multi-panel figure using PNG/JPEG images - r

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.

Answer 2

You can also rbind image arrays. But as they are 3D (x,y,RGB) you must use abind function from abind package. along=1 to bind vertically, 2 horizontally.
Works because image have same size.
img1 <- readPNG("filepath/img1.png")
img2 <- readPNG("filepath/img2.png")
img12 <- abind::abind(img1,img2,along=1)
png::writePNG(img12,"filepath/img12.png")

Answer 3

You can use magick package in R to do a collage.
# read the the png files into a list
pngfiles <-
list.files(
path = here::here("png_ouput_folder"),
recursive = TRUE,
pattern = "\\.png$",
full.names = T
)
# read images and then create a montage
# tile =2 , means arrange the images in 2 columns
# geometry controls the pixel sixe, spacing between each image in the collage output.
magick::image_read(pngfiles) %>%
magick::image_montage(tile = "2", geometry = "x500+10+5") %>%
magick::image_convert("jpg") %>%
magick::image_write(
format = ".jpg", path = here::here(paste(name,"_collage.jpg",sep="")),
quality = 100
)

Answer 4

As others have suggested the magick package is much simpler than a low-level solutions using grobs and related. magick is powerful but IMHO the documentation is poor and very circular.
However, there is a simple solution to your question in the page for image_montage(). The most important argument is the geometry specification, which governs the spacing between the "tiles."
library(magick)
input <- rep(logo, 12)
image_montage(input, geometry = 'x100+10+10', tile = '4x3', bg = 'pink', shadow = TRUE)
To get no spacing at all, use geometry = '0x100+0+0', shadow = FALSE".