imager now on CRAN, and a non-linear filtering example

September 17, 2015
By

[This article was first published on dahtah » R, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

imager is an R package for image processing that’s fairly fast and now quite powerful (if I may say so myself). It wraps a neat C++ library called CImg, by David Tschumperlé (CNRS). It took quite a bit of work, but imager is now on CRAN, so that installing it is as easy as:

install.packages("imager")

Here’s an example of using imager for max-filtering. A max-filter replaces each pixel value with the maximum value of its neighbours. Usually you’d write a loop, but we want to do things the R way (warning: this only works for small neighbourhoods, for reasons that will become obvious).

library(imager)
im <- load.image(system.file('extdata/parrots.png',package='imager'))
nhood <- expand.grid(dx=-2:2,dy=-2:2) #We want to include all pixels in a square 5x5 neighbourhood
im.s <- alply(nhood,1,function(d) imshift(im,d$dx,d$dy))

The result is a list of shifted versions of the image im (there are 5×5 = 25 different shifts, so you can imagine that you wouldn’t want to do this with a 20×20 neighbourhood and a large image!)
Now running a max (or min) filter is just a matter of calling pmax (or pmin):

max.filt <- do.call(pmax,im.s)
min.filt <- do.call(pmin,im.s)

Here’s our max-filtered image:

maxfilt

and here’s the min-filtered one:

minfilt

To leave a comment for the author, please follow the link and comment on their blog: dahtah » R.

R-bloggers.com offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.



If you got this far, why not subscribe for updates from the site? Choose your flavor: e-mail, twitter, RSS, or facebook...

Comments are closed.

Search R-bloggers

Sponsors

Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)