Cropping the top and bottom output of ggsave from grid.arrange of PNG Files

Question

library(grid)
library(gridExtra)
library(png)
library(ggplot2)

library(RCurl)

PNG_1 <- readPNG(getURLContent("https://i.ibb.co/MVx1QsQ/A.png"))
PNG_2 <- readPNG(getURLContent("https://i.ibb.co/kHVGNfQ/B.png"))
PNG_3 <- readPNG(getURLContent("https://i.ibb.co/yVf3Hjg/C.png"))

grid <- grid.arrange(rasterGrob(PNG_1), rasterGrob(PNG_2), rasterGrob(PNG_3), ncol=3)

ggsave(grid,filename="output.png")

Output.png

Tried to set the output dimensions manually, but to no avail.

Simply wish to remove the large top and bottom margins. Thanks.

Answer 1

As plots adapts to device size it's not simple to get part size. I think the easiest way is to compute aspect ratio from dimension of PNGs and provide device size to ggsave.

asp <- (ncol(PNG_1)+ncol(PNG_2)+ncol(PNG_3))/max(nrow(PNG_1),nrow(PNG_2),nrow(PNG_3))
ggsave(grid, filename= ..., width=5, height=5/asp)

to stitch those PNG you can use this code that will keep original pixel count. We can't use cbind/rbind function as readPNG returns arrays and not matrices. Fortunately the abind package provide a function to do it, abind( along=2 means cbind, along=1 for rbind)

library(abind)
PNG <- abind(PNG_1,PNG_2,PNG_3,along=2)
writePNG(PNG,"output.png")