Using image files on disk with R animation package - r

Question

I used R to create a series of images that took a long time to run. I'd like to use the animation package to make a video from them without re-running the analysis.
I can't find an example using existing images from file. The closest is Yihui Xie's demo('flowers') to create an HTML animation. I changed his code and can successfully make an mp4 of the flower images but I'm not sure how to access images already on file.
Based on his code, it should be something like this:
library(animation)
oopts = if (.Platform$OS.type == "windows") {
ani.options(ffmpeg = "C:/Software/ffmpeg/ffmpeg-20151015-git-0418541-win64-static/bin/ffmpeg.exe")}
#My list of images from disk
extList = list.files(myDir, pattern='.jpg', full.names=T)
saveVideo({
for (i in 1:length(extList)) {
#Yihui Xie's example downloads jpegs from web
#This code works to make an mp4 but I want to use images from disk
#extList = c('http://i.imgur.com/rJ7xF.jpg',
# 'http://i.imgur.com/Lyr9o.jpg',
# 'http://i.imgur.com/18Qrb.jpg')
#download.file(url = extList[i], destfile = sprintf(ani.options('img.fmt'), i), mode = 'wb')
someFunctionToAccessImage(extList[i])
}
}, video.name='notFlowers.mp4',
use.dev = FALSE,
ani.type = 'jpg',
interval = 2,
single.opts = "'dwellMultiplier': 1")
Bonus question - Can I do this with PNGs or other image types?

Answer 1

I found there to be a couple of problems with this. saveVideo uses a temporary directory to process the files and make the movie. Also, the postfix it was adding to the image name wasn't working correctly. So, here is a way to do it where you copy the images from the folder you have them stored in into the temporary directory used by saveVideo. The tricky part is finding the path to that directory, which is done using sys.frame from a function defined in the expression.
Note: another possible option could be to manually copy the images to the temporary folder that you know saveVideo will use (it will call tempdir()), or redefine tempdir() to return the path to your current images, but I haven't tested that.
library(animation)
oopts = if (.Platform$OS.type == "windows")
ani.options(ffmpeg = "C:\\home\\src\\ffmpeg-20151017-git-e9299df-win64-static\\bin\\ffmpeg.exe")
## Some variables
dirPath <- normalizePath("images/") # path to folder containing images
postfix <- "%03d" # I created my files with "Rplot%03d"
## Make the animation
saveVideo({
## Need to retrieve some variables from environments up the call stack
env.info <- (function() { list(wd = sys.frame(-1)$owd, fmt=sys.frame(-2)$img.fmt,
e=sys.frame(-2)) })()
postfix <- postfix
img.fmt <- gsub("%d", postfix, env.info$fmt, fixed=TRUE)
assign('img.fmt', img.fmt, envir=env.info$e)
file.copy(list.files(dirPath, full.names = TRUE), to=env.info$wd, overwrite = TRUE)
}, video.name='heatBalls.mp4', img.name='Rplot', interval = .05, use.dev=FALSE)
Full example
## Random function to save some images to disk
circ <- function(x,y,r) { s <- seq(-pi,pi,len=30); data.frame(x=x+r*cos(s), y=y+r*sin(s)) }
imgFun <- function(n, ncircs, dirPath) {
if (!require(scales)) stop("install scales package")
rads <- runif(ncircs, 0.5, 3)
xs <- runif(ncircs, 0.1+rads, 19.9-rads)
ys <- runif(ncircs, 0.1+rads, 19.9-rads)
vs <- matrix(runif(ncircs*2), 2)
cols <- colorRampPalette(c('lightblue','darkblue'), alpha=0.3)(ncircs)
png(file.path(dirPath, 'Rplot%03d.png'))
for (i in seq_len(n)) {
image(x=seq(0, 20, length=20), y=seq(0, 20, length=20),
z=matrix(rnorm(400),20), col=heat.colors(20, alpha=0.6), xlab='', ylab='')
for(j in 1:ncircs) polygon(x=circ(xs[j], ys[j], rads[j]), col=alpha(cols[j],0.7))
condx <- (xs + rads) > 20 | (xs - rads) < 0
condy <- (ys + rads) > 20 | (ys - rads) < 0
vs[1,condx] <- -vs[1,condx]
vs[2,condy] <- -vs[2,condy]
xs <- xs + vs[1,]
ys <- ys + vs[2,]
}
dev.off()
}
## Create some images on disk in a folder called "images"
dirPath <- normalizePath("images/")
dir.create(dirPath)
imgFun(50, 18, dirPath)
Then run the above code and a movie like the following should be made.