Image Recognition with R

imgrec provides an interface for image recognition using the Google Vision API. It includes functions to convert data for features such as object detection and optical character recognition to data frames. The package also includes functions for analyzing image annotations.

How to Install

You can download and install the latest development version of imgrec with the devtools package by running devtools::install_github('cschwem2er/imgrec').

For Windows users installing from github requires proper setup of Rtools, for which a tutorial is available here.

The package can also be installed from CRAN by running install.packages('imgrec').

How to Use

Authentification

Before loading imgrec you first need to initiate your authentification credentials. You need an API key from a Google Project with access permission for the Google Vision API. For this, you can first create a project using the Google Cloud platform. The setup process is explained in the API documentation. You will probably need to enable billing, but depending on your feature selection up to 1000 requests per month are free (see pricing). Next following the instructions for creating an API key. Finally, the API key needs to be set as environment variable before using the initialization function gvision_init():

Sys.setenv(gvision_key = "Your Google Vision API key")

In order to avoid calling Sys.setenv, you can permanently store the API key in your .Renviron. I recommend usethis::edit_r_environ() to find and edit your environment file.

Image annotations

Google Vision accepts common file types such as JPG, PNG, or BMP. Images can be passed to the function get_annotations, either as url strings or file paths to local images. In the following example, get_annotations is used to retrieve annotations for a poster of the Star Wars movie The Force Awakens.

The function returns a response object from the Google Vision API. It also recognizes if a user passes a character vector with multiple images. In this case, request batches are created automatically to reduce the number of required calls to the API. After retrieving annotations, raw data can be stored in an UTF-8 encoded JSON file:

temp_file_path <- tempfile(fileext = '.json')
save_json(results, temp_file_path)

While some users might prefer to work with raw .json data, which includes every single detail returned by the API, the structure is quite complex and deeply nested. To simplify the data, parse_annotations converts most of the features to data frames. For each feature, the original identifier of each image is included as img_id.

Once the features are converted to data frames, other R packages can be used to analyze the data. For instance, the labels data frame contains annotations about image content:

mid description score topicality img_id
/m/01n5jq Poster 0.9679052 0.9679052 https://upload.wikimedia.org/wikipedia/en/a/a2/Star_Wars_The_Force_Awakens_Theatrical_Poster.jpg
/m/02vxn Movie 0.9287522 0.9287522 https://upload.wikimedia.org/wikipedia/en/a/a2/Star_Wars_The_Force_Awakens_Theatrical_Poster.jpg
/m/03c31 Graphic design 0.7759998 0.7759998 https://upload.wikimedia.org/wikipedia/en/a/a2/Star_Wars_The_Force_Awakens_Theatrical_Poster.jpg
/m/0218rg Flyer 0.6593872 0.6593872 https://upload.wikimedia.org/wikipedia/en/a/a2/Star_Wars_The_Force_Awakens_Theatrical_Poster.jpg
/m/011s0 Advertising 0.6283476 0.6283476 https://upload.wikimedia.org/wikipedia/en/a/a2/Star_Wars_The_Force_Awakens_Theatrical_Poster.jpg

The package also extracts bounding polygons for logos, objects, faces and landmarks. We can for instance visualize all recognized logos of the Star Wars movie poster with magick and ggplot2:

Additional functions for feature analysis are currently in development.

Citation

If you use imgrec for your publications please consider citing it:

  Carsten Schwemmer (2019). imgrec: Image recognition with R. R package version 0.1.0.
  https://github.com/cschwem2er/imgrec

A BibTeX entry for LaTeX users is:

  @Manual{,
    title = {imgrec: Image recognition with R},
    author = {Carsten Schwemmer},
    year = {2019},
    note = {R package version 0.1.0},
    url = {https://github.com/cschwem2er/imgrec},
  }