qr_scan: Scan a file or image for QR codes.
In brianwdavis/quadrangle: Wrangle QR Codes Out of Images

qr_scan

R Documentation

Scan a file or image for QR codes.

Description

qr_scan reads in an image file or magick image object and first tries to read it using the C++ engine, which is fast and robust at locating the alignment patterns. However, it is less robust at decoding. If no codes can be read, the image and corners are passed to the JS engine, which is slower but has a higher success rate on cropped images.

Usage

qr_scan(
  image,
  flop = FALSE,
  lighten = FALSE,
  darken = TRUE,
  plot = FALSE,
  force_js = FALSE,
  no_js = FALSE,
  verbose = interactive()
)

Arguments

`image`	A path to a magick-readable file, e.g. jpg or png, or a magick object.
`flop`	Logical. Should the image be mirrored L-R before reading?
`lighten`	Logical. Should under-exposed areas of the image be lightened to increase contrast? Useful for images in shadow. Default `FALSE`.
`darken`	Logical. Should over-exposed areas of the image be darkened to increase contrast? Useful for images in bright light. Default `TRUE`.
`plot`	Logical. Should the image with any detected codes be shown after reading? (Requires ggplot2)
`force_js`	Logical. Should the JS library run even if the C++ library is able to read the code?
`no_js`	Logical. Never use the JS library, even if no QR codes are decoded.
`verbose`	Logical. Should warnings print for potentially slow operations?

Details

This function calls qr_scan_cpp and possibly qr_scan_js_from_corners. Each function has a double-while loop that progressively pushes mid-brightness pixels to pure black, and if that fails, progressively pushes mid-brightness pixels to pure white. This algorithm was developed for identifying QR codes on white printed sheets in outdoor images, in bright sun with or without shadows. To speed up scanning, you can use arguments lighten = F, darken = F which will skip any thresholding. If you use both lighten = T, darken = T, scanning may be quite slow until a decodable QR code is found. In those cases, a progress bar will attempt to be shown, if you have the progress package (https://github.com/r-lib/progress) available on your machine.

To BYO algorithm, you can use those two functions as templates. For example, image_morphology with (..., morphology = "Open", kernel = "Square:n") (varying n from 2 to 10) may repair corrupted QR blocks.