‘gifski’ as a bash command using R
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The gifski command-line utility is a
great tool to make a GIF animation from a series of
png files. At my work I’m using a laptop with Windows 10
and I don’t have admin rights. I don’t know how to install
gifski on this laptop.
But gifski is also the name of a R package which wraps the gifski command-line utility, and this package can be installed without difficulty. So I used this package and the optparse package to make my own bash command gifski, which is more convenient than the package.
Here is the script:
suppressPackageStartupMessages(library("optparse"))
suppressPackageStartupMessages(library("gifski"))
option_list <- list(
make_option(
"--frames", type = "character",
help = "png files given by a glob (e.g. pic*.png)"
),
make_option(
"--fps", type = "integer", default = 20L,
help = "frames per second (default 20)"
),
make_option(
c("-l", "--loop"), type = "integer", default = 0L,
help = "number of loops, 0 for infinite (the default)",
metavar = "number"
),
make_option(
c("-s", "--size"), type = "character", default = "512x512",
help = paste0(
"size of the gif given in the form WxH where W is the width in pixels ",
"and H is the height in pixels (default 512x512)"
),
metavar = "WxH"
),
make_option(
c("-b", "--backward"), action = "store_true", default = FALSE,
help = "loop forward and backward"
),
make_option(
c("-o", "--output"), type = "character", default = "animation.gif",
help = "output gif file (default animation.gif)",
metavar = "output.gif"
)
)
opt <- parse_args(OptionParser(
option_list = option_list, prog = "gifski"
))
# check options are correct
size_ok <- grepl("^\\d.*x\\d.*$", opt$size)
if(!size_ok)
stop("Invalid 'size' option.")
if(opt$fps <= 0)
stop("Invalid 'fps' option.")
if(opt$loop < 0)
stop("Invalid 'loop' option.")
png_files <- Sys.glob(opt$frames)
if(length(png_files) == 0L)
stop("Invalid 'frames' option.")
# if the user chooses the 'backward' option we duplicate the files
# in a temporary directory
if(opt$backward){
npngs <- 2L * length(png_files)
fmt <- paste0("pic%0", floor(log10(npngs) + 1), "d.png")
new_png_files <- file.path(tempdir(), sprintf(fmt, 1L:npngs))
file.copy(c(png_files, rev(png_files)), new_png_files)
png_files <- new_png_files
}
# get width and height
wh <- as.numeric(strsplit(opt$size, "x")[[1L]])
# a function to avoid some printed messages
quiet <- function(x) {
sink(tempfile())
on.exit(sink())
invisible(force(x))
}
# run gifski
quiet(gifski(
png_files = png_files,
gif_file = opt$output,
width = wh[1L],
height = wh[2L],
delay = 1/opt$fps,
loop = ifelse(opt$loop == 0L, TRUE, opt$loop)
))
cat("Output written to", opt$output)
Save this script where you want, say under the name gifski.R.
Now we make a bat file, say gifski.bat,
which will run this script:
@echo off echo. C:\path\to\Rscript.exe C:\path\to\gifski.R %*
That’s all. Put this bat file in a folder available in the
PATH environment variable and you can use the bash command
gifski. Here is the help which is displayed by the
command gifski --help:
Usage: gifski [options]
Options:
--frames=FRAMES
png files given by a glob (e.g. pic*.png)
--fps=FPS
frames per second (default 20)
-l NUMBER, --loop=NUMBER
number of loops, 0 for infinite (the default)
-s WXH, --size=WXH
size of the gif given in the form WxH where W is the width in pixels
and H is the height in pixels (default 512x512)
-b, --backward
loop forward and backward
-o OUTPUT.GIF, --output=OUTPUT.GIF
output gif file (default animation.gif)
-h, --help
Show this help message and exit
Note that there is an additional feature as compared to the original
gifski tool: the --backward option, which
allows to loop forward and backward.
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