Show a grid of equally spaced images with layout() and display() - r

Question

I want to create a grid of 9 images with equal spacing between them. Until now I managed to get something to work with par() and layout().
layout(matrix(1:9, widths=rep(lcm(4),9), heights=rep(lcm(3),9))
for (i in 1:9) {
imNew <- readImage(img_ar[i])
EBImage::display(imNew, method="raster")
}
gives me this
while using par:
layout(matrix(1:9, widths=rep(lcm(4),9), heights=rep(lcm(3),9))
for (i in 1:9) {
imNew <- readImage(img_ar[i])
EBImage::display(imNew,method="raster")
}
gives me this:
I also tried different options for par() like oma, mai and mar but these didn't change the spacing in between the individual images. What I like to have is an equal distance between the individual images like this:
Could anyone help me please?

Answer 1

You can use your original idea to separate images by including additional empty rows and columns in your layout, as in the following example. Note, however, that in order to achieve equal horizontal and vertical spacing you will need to tweak the device dimensions.
library(EBImage)
# load sample image
img <- readImage(system.file("images", "sample-color.png", package="EBImage"))
# downsample to reduce memory consumption and for faster processing
img <- resize(img, 192)
# build the layout matrix with additional separating cells
nx <- 4 # number of images in a row
ny <- 3 # number of images in a column
cols <- 2*nx-1
rows <- 2*ny-1
m <- matrix(0, cols, rows)
m[2*(1:nx)-1, 2*(1:ny)-1] <- 1:(nx*ny)
m <- t(m)
# relative spacing
pad <- .1
w <- rep(1, cols)
w[!(1:cols)%%2] <- pad
h <- rep(1, rows)
h[!(1:rows)%%2] <- pad * dim(img)[1L]/dim(img)[2L]
layout(m, widths = w, heights = h)
layout.show(nx*ny)
for (i in 1:(nx*ny)) {
display(img, method="raster")
}
A better approach is to use display() on an image stack. Then individual frames can be displayed arranged in a grid by setting all=TRUE.
## construct sample image stack
img_stack <- combine(replicate(nx*ny, img, simplify=FALSE))
display(img_stack, method="raster", all=TRUE)
Unfortunately, until recently it was not possible to adjust the spacing between the frames. To facilitate this, I've added an argument to display() specifying the spacing. Currently this new feature is available in the development version of EBImage, which can be obtained either from GitHub devtools::install_github("aoles/EBImage"), or from the Bioconductor devel branch.
The spacing can be provided as a fraction of frame dimensions (positive numbers <1) or in pixels (numbers >=1). Additionally, you can have different horizontal and vertical separation by providing a vector, e.g. spacing = (10, 20) will separate the columns by 10px, and the rows by 20px.
display(img_stack, method="raster", all=TRUE, spacing=.1)
Furthermore, you can add a margin around the grid, and control its layout by nx. The background can be set through bg passed to par().
Finally, a completely different way of drawing images in a grid is to construct one big composite image with tile. This approach might be useful, for example, when saving the result to a file. Note the additional border around the whole grid.
## tiled composite image
img_tiles <- tile(img_stack, nx=nx, lwd=20, fg.col="white", bg.col="white")
display(img_tiles, method="raster")

Answer 2

The ggplot2 way with marrangeGrob() from gridExtra:
library(RCurl)
library(png)
library(grid)
library(gridExtra)
library(ggplot2)
# read a few MNIST images
urls <- c('https://i.imgur.com/TEbkTqu.png', 'https://i.imgur.com/tnsjMFJ.png', 'https://i.imgur.com/VUZgJBs.png', 'https://i.imgur.com/FZ28d3w.png')
imgs <- list()
for (i in 1:length(urls)) {
imgs[[i]] <- readPNG(getURLContent(urls[i]))
}
# plot grid and show images
plist <- list()
for (i in 1:length(imgs)) {
plist[[i]] <- ggplot() +
annotation_custom(rasterGrob(imgs[[i]], interpolate=TRUE), xmin=-Inf, xmax=Inf, ymin=-Inf, ymax=Inf) +
labs(x = NULL, y = NULL) +
guides(x = "none", y = "none") +
theme_bw() +
theme(legend.position = "none", panel.border = element_blank(), panel.grid.major = element_blank(),
panel.grid.minor = element_blank())
}
marrangeGrob(plist, nrow=2, ncol=2, respect=TRUE)
(Demonstrated here in the shiny app too)