extract sentence using rtesseract

image_has_sentence.rb

# brew install tesseract
# gem install rtesseract
# gem install mini_magick
#
# example:
# puts image_has_sentence?('/Users/me/Pictures/hi.png', 'hello world')

require 'rtesseract'
require 'mini_magick'

def image_has_sentence?(image_path, sentence)
  image_output = Tempfile.new(%w[rtesseract jpg])
  
  # scale up and make grayscale. they said it works a charm. it does!
  MiniMagick::Tool::Convert.new do |convert|
    convert << image_path
    convert.merge! ['-resize', '200%', '-negate', '-set', 'colorspace', 'Gray']
    convert << image_output.path
  end

  # The secret here is the `psm` value. See `tesseract --help`. 
  # Different kind of image will benefit from certain psm value
  result = RTesseract.new(image_output.path, processor: 'mini_magick', psm: 1, debug: true)
  return (yield sentence).call result.to_s if block_given?
  result.to_s.include? sentence
end