classify a large collection of image files

Question

I have a large collection of image files for a book, andthe publisher wants a list where files are classified by "type" (greyscale graph, b/w halftone image, color image, line drawing, etc.). This is a hard problem in general, but perhaps I can do some of this automatically using image processing tools, e.g., ImageMagick with the R magick package.

I think ImageMagick is the right tool, but I don't really know how to use it for this purpose.

What I have is just a list of fig numbers & file names:

1.1 ch01-intro/fig/alcohol-risk.jpg
1.2 ch01-intro/fig/measels.png
1.3 ch01-intro/fig/numbers.png
1.4 ch01-intro/fig/Lascaux-bull-chamber.jpg
...

Can someone help get me started?

Edit: This was probably an ill-framed or overly-arching question as initially stated. I thought that ImageMagick identify or the R magick::image_info() function could help, so the initial question perhaps should have been: "How to extract image information from a list of files [in R]". I can pose this separately, if not already asked.

An initial attempt at this gave me the following for my first images,

library(magick)

# initialize an empty array to hold the results of `image_info`
figinfo <- data.frame(
  format=character(),
  width=numeric(),
  height=numeric(),
  colorspace=character(),
  matte=logical(),
  filesize=numeric(),
  density=character(), stringsAsFactors = FALSE
)

for (i in seq_along(files)) {
  img <- image_read(files[i])
  info <- image_info(img)
  figinfo[i,] <- info
}

I get:

> figinfo
  format width height colorspace matte filesize density
1   JPEG   661    733       sRGB FALSE    41884   72x72
2    PNG   838    591       sRGB  TRUE    98276   38x38
3    PNG   990    721       sRGB  TRUE   427253   38x38
4   JPEG   798    219       sRGB FALSE    99845 300x300

I conclude that this doesn't help much in answering the question I posed, of how to classify these images.

Edit2 Before closing this question, the advice to look into direct use of ImageMagick identify was helpful. https://imagemagick.org/script/escape.php In particular, the %[type] is closer to what I need. This is not exposed in magick::image_info(), so I may have to write a shell script or call system() in a loop.

For the record, here is how I can extract relevant attributes of these image files using identify directly.

# Get image characteristics via ImageMagick identify
# from: https://imagemagick.org/script/escape.php
#
# -format elements:
# %m image file format
# %f filename
# %[type] image type
# %k number of unique colors
# %h image height in pixels
# %r image class and colorspace

identify -format "%m,%f,%[type],%r,%k,%hx%w" imagefile

>identify -format "%m,%f,%[type],%r,%k,%hx%w" Quipu.png
PNG,Quipu.png,GrayscaleAlpha,DirectClass Gray Matte,16,449x299

The %[type] attribute takes me towards what I want.

I do not know R or Rmagick. But in command line Imagemagick you can use the string formats for colorspace and type to get most of the information you want. `convert image -format "%[colorspace]" info:` for example. See https://imagemagick.org/script/escape.php — fmw42, May 20 '19 at 05:46

score 0 · Answer 1 · answered May 28 '19 at 15:15

To close this question:

In an R context, I was successful in using system(, intern=TRUE) for this task, as follows, with some manual fixups

# Use identify directly via system()

# function to run identify for one file
get_info <- function(file) {
  cmd <- 'identify -quiet -format "%f,%m,%[type],%r,%h,%w,%x,%y"'
  info <- system(paste(cmd, file), intern=TRUE)
  unlist(strsplit(info, ","))
}

# This doesn't cause coercion to numeric
figinfo <- data.frame(
  filename=character(),
  format=character(),
  type=character(),
  class=character(),
  height=numeric(),
  width=numeric(),
  xres=numeric(),
  yres=numeric(),
  stringsAsFactors = FALSE
)


for (i in seq_along(files)) {
  info <- get_info(files[i])
  info[4] <- sub("DirectClass ", "", info[4])
 figinfo[i,] <- info
}

figinfo$height <- as.numeric(figinfo$height)
figinfo$width <- as.numeric(figinfo$width)
figinfo$xres=round(as.numeric(figinfo$xres))
figinfo$yres=round(as.numeric(figinfo$yres))

Then I have more or less what I want:

> str(figinfo)
'data.frame':   161 obs. of  8 variables:
 $ filename: chr  "mileyears4.png" "alcohol-risk.jpg" "measels.png" "numbers.png" ...
 $ format  : chr  "PNG" "JPEG" "PNG" "PNG" ...
 $ type    : chr  "Palette" "TrueColor" "TrueColorAlpha" "TrueColorAlpha" ...
 $ class   : chr  "PseudoClass sRGB " "sRGB " "sRGB Matte" "sRGB Matte" ...
 $ height  : num  500 733 591 721 219 ...
 $ width   : num  720 661 838 990 798 ...
 $ xres    : num  72 72 38 38 300 38 300 38 28 38 ...
 $ yres    : num  72 72 38 38 300 38 300 38 28 38 ...
>

classify a large collection of image files

1 Answers1