Support for hOCR and Tesseract 4 in R

Earlier this month we released a new version of the tesseract package to CRAN. This package provides R bindings to Google’s open source optical character recognition (OCR) engine Tesseract.

Two major new features are support for HOCR and support for the upcoming Tesseract 4.

🔗 hOCR output

Support for HOCR output was requested by one of our users on Github. The ocr() function gains a parameter HOCR which allows for returning results in hOCR format:

library(tesseract)

# Text output
text <- ocr("https://jeroen.github.io/images/testocr.png")
cat(text)

# hOCR output
xml <- ocr("https://jeroen.github.io/images/testocr.png", HOCR = TRUE)
cat(xml)

hOCR is an open standard of data representation for formatted text obtained from OCR (wikipedia). The definition encodes text, style, layout information, recognition confidence metrics and other information using XML.

Every word in the hOCR output includes meta data such as bounding box, confidence metrics, etc. With a little xml2 and regular expression magic we can extract a beautiful data frame:

library(tesseract)
library(xml2)
library(stringr)
library(tibble)
xml <- ocr("https://jeroen.github.io/images/testocr.png", HOCR = TRUE)
doc <- read_xml(xml)
nodes <- xml_find_all(doc, ".//span[@class='ocrx_word']")
words <- xml_text(nodes)
meta <- xml_attr(nodes, 'title')
bbox <- str_replace(str_extract(meta, "bbox [\\d ]+"), "bbox ", "")
conf <- as.numeric(str_replace(str_extract(meta, "x_wconf.*"), "x_wconf ", ""))
tibble(confidence = conf, word = words, bbox = bbox)

# A tibble: 60 x 3
   confidence word  bbox          
        <dbl> <chr> <chr>         
 1       89.0 This  36 92 96 116  
 2       89.0 is    109 92 129 116
 3       92.0 a     141 98 156 116
 4       93.0 lot   169 92 201 116
 5       91.0 of    212 92 240 116
 6       91.0 12    251 92 282 116
 7       92.0 point 296 92 364 122
 8       89.0 text  374 93 427 116
 9       93.0 to    437 93 463 116
10       90.0 test  474 93 526 116
# ... with 50 more rows

So this gives us a little more information about the OCR results than just the text.

🔗 Upcoming Tesseract 4

The Google folks and contributors are working very hard on the next generation the Tesseract OCR engine which uses new neural network system based on LSTMs, with major accuracy gains. The release of Tesseract 4 is scheduled for later this year but an alpha release is already available.

Our latest CRAN release of the tesseract now has the required changes to support Tesseract 4. On MacOS you can already give this try this by installing tesseract from the master branch:

brew remove tesseract
brew install tesseract --HEAD

After updating tesseract you need to reinstall the R package from source:

install.packages("tesseract", type = "source")

This is still alpha, things may break. Report problems in our github repository.