quick technote about qr code scanner

Author: jeroen

content/blog/2023-10-30-opencv-qr/index.md

@@ -0,0 +1,61 @@
+---
+slug: opencv-qr
+title: 'Scanning QR codes in R'
+date: '2023-10-30'
+author: Jeroen Ooms
+description: 'The new version of the opencv package includes a cool QR code scanner.'
+photogallery: true
+tags:
+  - tech notes
+  - packages
+  - opencv
+---
+
+The latest version of the [opencv R package](https://ropensci.r-universe.dev/opencv) can detect and decode QR codes!
+
+```r
+# Install latest opencv
+install.packages("opencv", repos = "https://ropensci.r-universe.dev")
+```
+
+There are two ways of using this: the [`ocv_qr_detect`](https://docs.ropensci.org/opencv/reference/qrcode.html) function tries to find the QR in an image file. It returns either a text string, or NULL if no QR code was found in the image:
+
+```r
+img <-  opencv::ocv_read('https://jeroen.github.io/images/qrtest.jpg')
+opencv::ocv_qr_detect(img)
+## https://www.r-project.org
+```
+
+Alternatively if your laptop has a camera, you can use R as a true QR code scanner! The [`qr_scanner`](https://docs.ropensci.org/opencv/reference/qrcode.html) function starts the camera device and filters the video stream through the above `ocv_qr_detect` until a QR code has been detected.
+
+```r
+# This requires a camera
+txt <- opencv::qr_scanner()
+```
+
+By default, both `ocv_qr_detect` and `qr_scanner` return the text value of the decoded QR code. But both functions also have an option `draw = TRUE` which will instead return an annotated image with the position and value of the QR drawn into the image, and qr text value as an attribute.
+
+
+{{< gallery >}}
+{{< figureforgallery src="input.jpg" alt="Input photo which includes a QR code" >}}
+{{< figureforgallery src="output.jpg" alt="Annotated output which shows the input plus highlighted QR area" >}}
+{{< /gallery >}}
+
+## Generating QR codes in R
+
+There exists another package on CRAN called [qrcode](https://thierryo.github.io/qrcode/) (currently maintained by Thierry Onkelinx) which can generate most types of QR codes using R graphics, which is super cool.
+
+We can combine the two packages to roundtrip text to QR codes in R:
+
+```r
+## generate a qr code image
+png("qr-test.png")
+plot(qrcode::qr_code("This is a test!"))
+dev.off()
+
+# Verify that we can read it:
+ocv_qr_detect(ocv_read('qr-test.png'))
+## [1] "This is a test!"
+```
+
+So this provides a quick way to exchange small blobs of information between computers running R, without the need for any network connection.