Animate .gif images in R / ImageMagick

Yesterday I surfed the web looking for 3D wireframe examples to explain linear models in class. I stumbled across this site whereanimated 3D wireframe plots are outputted by SAS.  Below I did something similar in R. This post shows the few steps of how to create an animated .gif file using R and ImageMagick. Here I assume that you have ImageMagickinstalled on your computer. As far as I know it is also possible to produce animated .gif files using R only, e.g. with write.gif() from thecaTools package. But using ImageMagick is straighforward, gives you control over the conversion and .gif production and is the free standard program for conversion. 

First a simple countdown example. To be sure not to overwrite anything I will create a new folder and set the working directory to the new folder.

dir.create("examples")
setwd("examples")

# example 1: simple animated countdown from 10 to "GO!".
png(file="example%02d.png", width=200, height=200)
  for (i in c(10:1, "G0!")){
    plot.new()
    text(.5, .5, i, cex = 6)
  }
dev.off()

# convert the .png files to one .gif file using ImageMagick. 
# The system() function executes the command as if it was done
# in the terminal. the -delay flag sets the time between showing
# the frames, i.e. the speed of the animation.
system("convert -delay 80 *.png example_1.gif")

# to not leave the directory with the single jpeg files
# I remove them.
file.remove(list.files(pattern=".png"))

Above a loop is used to do the plotting. A new .png file for each plot is created automatically. The "%02d" part in the  filenamepart is a placeholder here for a two character counter (01,02 etc.). So we do not have to hard-code the filename each time.

Now I want a linear model to be visualized as a 3d mesh.  A 3D surface can easily be plotted using the wireframe() function from the lattice package (or other functions available in R; also see the rgl package for rotatable 3D output).

library(lattice)
b0 <- 10
b1 <- .5
b2 <- .3
g <- expand.grid(x = 1:20, y = 1:20)
g$z <- b0 + b1*g$x + b2*g$y
wireframe(z ~ x * y, data = g)

# to rotate the plot
wireframe(z ~ x * y, data = g,
          screen = list(z = 10, x = -60))

Now let’s create multiple files while changing the rotation angle. Note thatwireframe() returns a trellis object which needs to be printed explicitly here usingprint(). As the code below produces over 150 images and merges them into one .gif file note that this may take a minute or two.

# example 2
png(file="example%03d.png", width=300, heigh=300)
  for (i in seq(0, 350 , 10)){
    print(wireframe(z ~ x * y, data = g,
              screen = list(z = i, x = -60)))
  }
dev.off()
# convert pngs to one gif using ImageMagick
system("convert -delay 40 *.png example_2_reduced.gif")

# cleaning up
file.remove(list.files(pattern=".png"))

 

Now I want the same as above but for a model with an interaction and I want to make the plot a bit more pretty. This time I use .pdf as output file. This is just to demonstrate that other formats than .png can be used. Note that the "%02d" part of the filename has disappeared as I only create one .pdf file with multiple pages, not multiple .pdf files.

# example 3
b0 <- 10
b1 <- .5
b2 <- .3
int12 <- .2
g <- expand.grid(x = 1:20, y = 1:20)
g$z <- b0 + b1*g$x + b2*g$y + int12*g$x*g$y

pdf(file="example_3.pdf", width=4, height=4)
  for (i in seq(0, 350 ,10)){
    print(wireframe(z ~ x * y, data = g,
              screen = list(z = i, x = -60),
              drape=TRUE))
  }
dev.off()
# convert pdf to gif using ImageMagick
system("convert -delay 40 *.pdf example_3_reduced.gif")
# cleaning up
file.remove(list.files(pattern=".pdf"))

The last example is a visual comparison of the interaction and a non-interaction model. Here we now have the models on the same scale. Before I did not specify the scale limits.

# example 4
b0 <- 10
b1 <- .5
b2 <- .3
int12 <- .2
g <- expand.grid(x = 1:20, y = 1:20)
z <- c( b0 + b1*g$x + b2*g$y,
        b0 + b1*g$x + b2*g$y + int12*g$x*g$y)
g <-rbind(g, g)
g$z <- z
g$group <- gl(2, nrow(g)/2, labels=c("interaction", "no interaction"))

png(file="example%03d.png", width=300, height=300)
  for (i in seq(0, 350 ,10)){
    print(wireframe(z ~ x * y, data = g, groups=group,
              screen = list(z = i, x = -60)))
  }
dev.off()
# convert pngs to one gif using ImageMagick
system("convert -delay 40 *.png example_4.gif")

# cleaning up
file.remove(list.files(pattern=".png"))

Above I chose a small image size (300 x 300 pts). Smaller steps for rotation and a bigger picture size increases file sizes for examples 2, 3 and 4 to 3-5mb which is far too big for a web format. I am not familiar with image optimization and I suppose a smaller file sizes for the .gif file can easily be achieved by some optimization flags in ImageMagick. Any hints are welcome!

http://ryouready.wordpress.com/2010/11/21/animate-gif-images-in-r-imagemagick/