Luis D. Verde Arregoitia

Luis D. Verde Arregoitia

data . ecology . evolution . conservation . biogeography . mammals

Download, batch process, and tile images

<!DOCTYPE html>

hexout
created with hexsession

As I continue to work on the hexsession package, which now works for arbitrary sets of images, here’s a walkthrough of the steps needed to:

  • download random dog images from the Dog CEO API
  • batch resize the images and make them black and white
  • make a hexagonal tile of the images, each with an optional URL

I keep forgetting how to do the first two steps, so hopefully others find this helpful and I can also come back to this when I get stuck.

The final output is embedded above, which is pretty nice and this kind of thing can be used for software packages, or maybe for people in an organization with headshots and links to each member’s profile.

As usual, the code in these blocks below should be reproducible as long as you have an internet connection and the relevant packages installed.

Download dog photos

Let’s download dog photos from the Dog CEO API. This API serves images for different breeds, built from the Stanford Dogs Dataset plus community contributions. We can use httr2 to send a GET request to the API and retrieve a list of image URLs. To be nice to the servers I did all the iteration here slowly with purrr. First we get the list of breeds, select some at random, add two that I like, and them download the photos.

library(httr2)
library(purrr)
library(stringr)
library(magick)

# define fn to get a random image for a breed
randomDog <- function(breed) {
  # build URL
  url <- paste0("https://dog.ceo/api/breed/", breed, "/images/random")
  #  request
  req <- request(url)
  resp <- req |>
    req_perform()
  # JSON response
  data <- resp_body_json(resp)
  data$message
}

# get all the breeds
allbreeds <- 
  request("https://dog.ceo/api/breeds/list") |> 
  req_perform() |>
  resp_body_json()
breedsvec <- simplify(allbreeds$message)

# being nice
rate <- rate_delay(0.8)
# wrap the new fn in slowly
slow_randomdog <- slowly(\(x) randomDog(x), rate = rate, quiet = FALSE)
# 15 random breeds plus two that I like
randomdogsvec <- sample(breedsvec, 15)
randomdogsvec <- c(randomdogsvec, "mastiff/bull","retriever/golden")
# get the image urls
dogphotourls <- map(randomdogsvec, slow_randomdog)

# folder and paths to save the images
fs::dir_create("dogimgs")
savepaths <- paste0("dogimgs/",str_replace(randomdogsvec,"/","-"),".jpg") 
slowdl <- slowly(\(x,y) download.file(x,y), rate = rate, quiet = FALSE)
walk2(dogphotourls,savepaths,\(x,y) slowdl(x,y))

Batch process the photos

We can use magick to resize all the images to a uniform height of 230px, desaturate them, and export each one to disk in a new folder. The trick here was to apply as.list() to the magick image stack in the final step.

# process images
# folder and paths for the processed images
fs::dir_create("dogimgs/processedimgs")
processedimgpaths <- paste0("dogimgs/processedimgs/",basename(savepaths))

# read and process
allimgs <- image_read(savepaths)
procimgs <- allimgs |> 
  image_scale("230x") |>  # resize
  image_convert(colorspace = 'gray') |> # desaturate
  image_contrast() # enhance contrast 

# write to disk
walk2(as.list(procimgs),processedimgpaths,\(x,y) image_write(x,y))

Create the tile

Now that hexsession takes arbitrary sets of image paths, we can just build a tile with a vector of paths. I added the same url to each image just to show that the html output works.

# restart session to detach any loaded packages
dogpaths <- fs::dir_ls("dogimgs/processedimgs/")
cturls <- rep("https://betterpet.com/why-are-dogs-so-cute/",length(dogpaths))
hexsession::make_tile(local_images = dogpaths,local_urls = cturls)

To embed the output in this post, I put the self-contained html file in _includes/ and refer to it with {% include %} .

nice!

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