Class: DerivativeRodeo::Generators::HocrGenerator

Inherits:
BaseGenerator
  • Object
show all
Defined in:
lib/derivative_rodeo/generators/hocr_generator.rb

Overview

Responsible for finding or creating a hocr file (or configured :output_suffix) using tesseract. Will create and store a monochrome derivative if one is not found.

From tesseract -h

Usage:
tesseract --help | --help-extra | --version
tesseract --list-langs
tesseract imagename outputbase [options...] [configfile...]

See Also:

Defined Under Namespace

Modules: RequiresExistingFile

Class Attributes collapse

Attributes inherited from BaseGenerator

#input_uris, #output_extension, #output_location_template, #preprocessed_location_template

Instance Method Summary collapse

Methods inherited from BaseGenerator

#derive_preprocessed_template_from, #destination, #generated_files, #generated_uris, #initialize, #input_files, #run, #valid_instantiation?

Constructor Details

This class inherits a constructor from DerivativeRodeo::Generators::BaseGenerator

Instance Attribute Details

#additional_tessearct_options ⇒ Object

Additional options to send to tesseract command; default nil.



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# File 'lib/derivative_rodeo/generators/hocr_generator.rb', line 33

class_attribute :additional_tessearct_options, default: nil

#command_environment_variables ⇒ Object

Command arena variables to for tesseract command; default nil. Should be a space seperated string of KEY=value pairs

Examples:

# this works for space_stone aws lambda
Derivative::Rodeo::Step::HocrStep.command_environment_variables =
  'OMP_THREAD_LIMIT=1 TESSDATA_PREFIX=/opt/share/tessdata LD_LIBRARY_PATH=/opt/lib PATH=/opt/bin:$PATH'


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# File 'lib/derivative_rodeo/generators/hocr_generator.rb', line 28

class_attribute :command_environment_variables, default: "OMP_THREAD_LIMIT=1"

#output_suffix ⇒ Object

The tesseract command's output base; default :hocr.



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# File 'lib/derivative_rodeo/generators/hocr_generator.rb', line 37

class_attribute :output_suffix, default: :hocr

Instance Method Details

#build_step(output_location:, input_tmp_file_path:) ⇒ StorageLocations::BaseLocation

Run tesseract on monocrhome file and store the resulting output in the configured output_extension (default 'hocr')

Parameters:

Returns:

See Also:

  • #requisite_files


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# File 'lib/derivative_rodeo/generators/hocr_generator.rb', line 52

def build_step(output_location:, input_tmp_file_path:, **)
  tesseractify(input_tmp_file_path, output_location)
end

#run_tesseract(in_path, out_path) ⇒ Object

Parameters:

  • in_path (String) —

    the source of the file

  • out_path (String) 


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# File 'lib/derivative_rodeo/generators/hocr_generator.rb', line 95

def run_tesseract(in_path, out_path)
  # we pull the extension off the output path, because tesseract will add it back
  cmd = ""
  cmd += command_environment_variables + " " if command_environment_variables.present?
  # TODO: The line of code could mean we had a file with multiple periods and we'd just
  # replace the first one.  Should we instead prefer the following:
  #
  # `out_path.split(".")[0..-2].join('.') + ".#{output_extension}"`
  output_to_path = out_path.sub('.' + output_extension, '')
  cmd += "tesseract #{in_path} #{output_to_path}"
  cmd += " #{additional_tessearct_options}" if additional_tessearct_options.present?
  cmd += " #{output_suffix}"

  # TODO: capture output in case of exceptions; perhaps delegate that to the #run method.
  run(cmd)
end

#tesseractify(input_tmp_file_path, output_location) ⇒ Object

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Call tesseract on the monochrome file and store the resulting hocr in the tmp_path

Parameters:



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# File 'lib/derivative_rodeo/generators/hocr_generator.rb', line 86

def tesseractify(input_tmp_file_path, output_location)
  output_location.with_new_tmp_path do |out_tmp_path|
    run_tesseract(input_tmp_file_path, out_tmp_path)
  end
end

#with_each_requisite_location_and_tmp_file_path(builder: MonochromeGenerator) {|file, tmp_path| ... } ⇒ Object

When generating a hocr file from an image, we've found the best results are when we're processing a monochrome image. As such, this generator will auto-convert a given image to monochrome.

Parameters:

Yield Parameters:

See Also:



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# File 'lib/derivative_rodeo/generators/hocr_generator.rb', line 67

def with_each_requisite_location_and_tmp_file_path(builder: MonochromeGenerator)
  mono_location_template = Services::ConvertUriViaTemplateService.coerce_pre_requisite_template_from(template: output_location_template)

  requisite_files ||= builder.new(input_uris: input_uris, output_location_template: mono_location_template).generated_files
  requisite_files.each do |input_location|
    input_location.with_existing_tmp_path do |tmp_file_path|
      yield(input_location, tmp_file_path)
    end
  end
end