Working with text and using OCR features

New in version 2.0.2.

OCR Summary

Note

… important for version 2.0.2+

Though the class names TextOCR (Python scripts) and TextRecognizer (Java API level) are still supported, they are deprecated. So you should not use them with new works anymore.

In both environments it is now the class name OCR.

On top TextOCR.start() or TextRecognizer.start() are no longer needed beforehand (all methods are static).

Simply start using the text/OCR features with Region or Image (see the summary below).

In special cases, where you need to tweak the OCR engine, you can use the OCR features directly (see the summary below).

SikuliX uses the Java library Tess4j, that allows to use the Tesseract features at the Java level. Internally it depends on Tesseract,

If you want to know anything about features not mentioned here or supported by SikuliX that are available in Tess4J/Tesseract, you have to dive into the details on the respective home pages of the packages.

There are three feature groups (for method specs follow the links):

Special Information for SikuliX version 2 - Lessons learned and BestPractices (incl. features under developement and/or evaluation)

Accuracy of text recognition (confidence)

According to the recommendations of Tesseract and experiences found in the net, SikuliX does some optimization of the images before handing over to OCR:

  • convert to grayscale
  • do some edge sharpening
  • revert images with light text on dark background to black on white
  • resize the image to an optimum size
On the latter (optimum size) some comments:
  • with Tessreact 3 the recommendation was to rezize to an image of 200 - 300 dpi
  • with Tesseract 4 the best practice seems to be: resize to a size, where the average height of a capital letter (preferably the X) has a height of about 30 pixel

Both variants have drawbacks, but the pixel approach seems to be the most promising (own tests and experiences from the net). The dpi approach works too with slightly lower accuarcy, but is too dependent on the current screen settings, which in turn are differently handled by Java in different system environments.

To not make usage too complicated in the average, SikuliX comes with the following default:

The height of a capital X in the default font used in Java in the current screen environment is taken as the base for the resize to 30 pixel.

There are functions/methods, that allow to tweak this optimization process - see Options.optimization.

If you have problems with accuarcy, then before fiddling around with the height/size options have a look at the Lessons learned and BestPractices.

There are functions/methods (classes Region, Image, OCR), that tell The OCR engine, to treat the image as a single line, a single word or even a single character. In some cases their usage might help to get what you expect.

Generally it makes sense, to try with a sample before investing in complex code:

TODO: Example script to be added

If your interested in the reported accuracy (confidence), you have to use one of the SikuliX features, that return text matches:

match.getScore()

which returns a decimal value between 0 and 1 (meant as percentage). Very good values are above 0.95, good values above 0.90.

To get the text in such cases, simply use:

match.getText()

Note

Even if a good confidence is reported, there might still be very few errors in the returned text, though the risk is very small. If you need exact results in case you have to intelligently combine the SikuliX and Tesseract features. Even lower confidence values do not mean, that the text is not correctly recognized. Suggestions and contributions are always very welcome.

Handling OCR options

There is one global options set (OCR.Options), that is used if nothing else is said.

Using myOptions = OCR.Options() you can create a new options set, derived from the initial global options. This can be modified using the setters shown below (myOptions.XXX(value)) and later be used with features allowing to specify an option set to use.

As well you can apply the setters to the global options (OCR.globalOptions().XXX(value)), to run OCR with specific defaults. At any time, you can reset the global options to its initial state using reset().

status() reports the currently used global options (example for Windows 10 with standard screen settings):

Global settings OCR.options:
data = ...some-path.../tessdata
language(eng) oem(3) psm(3) height(15,1) factor(1,99) dpi(96) LINEAR
configs: conf1, conf2, ...
variables: key:value, ...

The information is usually not relevant, only in cases where you want to report a problem or you are using non-standard SikuliX-OCR-features. More Details you may find below.

For a specific options set (created before using someOptions = OCR.Options()) you can use (Java) someOptions.toString() to get this information as text (use print someOptions in scripts).

The options setters can be chained:

myOptions = OCR.Options().setter(value).setter(value)...

or used alone:

myOptions = OCR.Options()
myOptions.setter(value)
myOptions.setter(value)

Note

… on running scripts in the IDE

After a script run, OCR is reset to the defaults of OEM, PSM and text height. If Tesseract variables and/or configs have been set, those are removed as well. So each script run starts with a defined default state of the Tesseract engine.

OCR engine mode (OEM)

The latest version of Tesseract (namely version 4) internally uses a new detection engine (LSTM), that has again raised accuracy and speed. If the corresponding language models are supplied at runtime (which is the case with SikuliX now), then this engine is used as a default (OEM = 3).

see Options.oem()

Normally there should be no need to run another engine mode.

OCR page segmentation mode(PSM)

You can set the page segmentation mode (PSM), which tells Tesseract, how to split the given image into rectangles, that are supposed to contain readable text.

see Options.psm()

Only in special cases there should be a need to use something else than the default (3).

Switch to another language

In the standard SikuliX runs the text features with the english language set, which is bundled with SikuliX. It is possible to add more languages to your SikuliX setup and switch between the installed languages at runtime.

These are the steps to switch to another language than the standard english (eng):

Step 1: Find the folder SikulixTesseract/tessdata in your SikuliX <app-data> folder (see docs)

Step 2: Download the languages needed from Tesseract languages (only the files with .traineddata)

For SikuliX version 2.0.x+ we use the files for Tesseract 4 (preferably those from tessdata_fast)

For earlier Versions up to 1.1.3 use the files for Tesseract 3 (no longer supported).

Step 3: Put the .traineddata files into the tessdata folder (Step 1)

In your script, that should use the language, say before using an OCR feature (Options.language()):

OCR.globalOptions().language(xxx)

Another way to set a default language to be used after startup globally:

Settings.OcrLanguage = "xxx"

This is then recognized with each subsequent script start in the same IDE session.

Have your own Tesseract datapath

Instead of the above mentioned standard you can have your own folder with all stuff, that is needed by Tesseract at runtime. If you want to do that, simply have:

Settings.OcrDataPath = <some absolute Path>

Before starting the Textrecognizer. Take care, that all relevant files are in a subfolder tessdata.

This is then recognized with each subsequent script start in the same IDE session.

Use Options.dataPath() to switch the path dynamically:

OCR.globalOptions().dataPath(someAbsolutePath)

Other possibilities to tweak the Tesseract OCR process

About Tesseract variables, configurations, training and other gory details you have to consult the Tesseract documentation.

But before you step into Tesseract you should read about LessonsLearned and BestPractices.

To set a variable as a single Tesseract setting, that controls a specific topic in the OCR process use Options_variable()

To set a configuration which is a file containing a set of variables, that configure the behaviour of a tailored OCR process use Options_configs().

The Text and OCR features in Detail (Class OCR)

class OCR
Static helper class for OCR via Tess4J/Tesseract.

The methods in this class are not threadsafe.

Global stuff for OCR

OEM
OCR Engine modes.

0 TESSERACT_ONLY Tesseract Legacy only.
1 LSTM_ONLY LSTM only.
2 TESSERACT_LSTM_COMBINED LSTM + Legacy.
3 DEFAULT Default, based on what is available. (DEFAULT)

Usage: OCR.OEM.MODE
PSM
Page segmentation modes.

0 OSD_ONLY Orientation and script detection (OSD) only.
1 AUTO_OSD Automatic page segmentation with OSD.
2 AUTO_ONLY Automatic page segmentation, but no OSD, or OCR.
3 AUTO Fully automatic page segmentation, but no OSD. (Default)
4 SINGLE_COLUMN Assume a single column of text of variable sizes.
5 SINGLE_BLOCK_VERT_TEXT Assume a single uniform block of vertically aligned text.
6 SINGLE_COLUMN Assume a single uniform block of text.
7 SINGLE_LINE Treat the image as a single text line.
8 SINGLE_WORD Treat the image as a single word.
9 CIRCLE_WORD Treat the image as a single word in a circle.
10 SINGLE_CHAR Treat the image as a single character.
11 SPARSE_TEXT Sparse text. Find as much text as possible in no particular order.
12 SPARSE_TEXT_OSD Sparse text with OSD.
13 RAW_LINE Raw line. Treat the image as a single text line, bypassing hacks that are Tesseract-specific.

Usage: OCR.PSM.MODE
classmethod globalOptions()
access/get the current global Options as singleton.
Returns:(Options) the global Options
classmethod reset()
Resets the global options to the initial defaults.

oem = OcrEngineMode.DEFAULT.ordinal();
psm = PageSegMode.AUTO.ordinal();
language = Settings.OcrLanguage;
dataPath = null; //(see comment)
textHeight = getDefaultTextHeight();
variables.clear();
configs.clear();

comment on dataPath==null: dataPath will be evaluated at the next use of an OCR feature
to the SikuliX default or Settings.OcrDataPath (if set)
Returns:(Options) the global Options
classmethod status()
prints out the current global options.

Read text

classmethod readText(SFIRBS from)
Reads text from the given source.
Uses the global options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
Returns:

(String) text

classmethod readText(SFIRBS from, Options options)
Reads text from the given source.
Uses the given options
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
  • options – Options to be used
Returns:

(String) text

Read or get lines of text

classmethod readLine(SFIRBS from)
Reads text from the given source (line).
assuming the source contains a single line of text.
Uses the global options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
Returns:

(String) text

classmethod readLine(SFIRBS from, Options options)
Reads text from the given source (line).
assuming the source contains a single line of text.
Uses the given options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
  • options – options for the used TextRecognizer
Returns:

(String) text

classmethod readLines(SFIRBS from)
Treats text from the given source as lines.
Uses the global options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
Returns:

(List<Match>) lines as a list of matches

classmethod readLines(SFIRBS from, Options options)
Treats text from the given source as lines.
Uses the given options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
  • options – options for the used TextRecognizer
Returns:

(List<Match>) lines as a list of matches

Read or get words of text

classmethod readWord(SFIRBS from)
Reads text from the given source (word).
assuming the source contains a single word of text.
Uses the global options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
Returns:

(String) text

classmethod readWord(SFIRBS from, Options options)
Reads text from the given source (word).
assuming the source contains a single word of text.
Uses the given options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
  • options – options for the used TextRecognizer
Returns:

(String) text

classmethod readWords(SFIRBS from)
Treats text from the given source as words.
Uses the global options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
Returns:

(List<Match>) words as alist of matches

classmethod readWords(SFIRBS from, Options options)
Treats text from the given source as words.
Uses the given options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
  • options – options for the used TextRecognizer
Returns:

(List<Match>) words as a list of matches

Assume the text is one character

classmethod readChar(SFIRBS from)
Reads text from the given source (character).
assuming the source contains a single character.
Uses the global options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
Returns:

(String) text

classmethod readChar(SFIRBS from, Options options)
Reads text from the given source (character).
assuming the source contains a single character.
Uses the given options.
Parameters:
  • <SFIRBS> – File name, File, Image, Region, BufferdImage or ScreenImage
  • from – source to read text from
  • options – options for the used TextRecognizer
Returns:

(String) text

The options set for OCR

class OCR.Options
A container for the options relevant for using OCR on
Region or Image.
Use OCR.Options() to get a new option set
use OCR.globalOptions() to access the global options

In case you have to consult the Tesseract docs

Global stuff for OCR.Options

Options()
create a new Options set from the initial defaults settings.

about the default settings see OCR.reset()
clone()
makes a copy of this Options
Returns:(Options) new Options as copy
reset()
resets this Options set to the initial defaults.
see OCR.reset()
Returns:(Options) this
toString()
Current state of this Options as some formatted lines of text.

OCR.Options:
data = …some-path…/tessdata
language(eng) oem(3) psm(3) height(15,1) factor(1,99) dpi(96)
configs: conf1, conf2, …
variables: key:value, …
Returns:(String) a text string as before

Handle OEM - OCR Engine Mode

oem()
get this OEM.
see OEM
Returns:(int) oem as int
oem(int oem)
set this OEM.
see OEM
Parameters:oem – as int
Returns:(Options) this Options
oem(OEM oem)
set this OEM.
see OEM
Parameters:oem – as enum constant
Returns:(Options) this Options

Handle PSM - Page Segmentation Mode

psm()
get this PSM.
see PSM
Returns:(int) psm as int
psm(int psm)
set this PSM.
see PSM
Parameters:psm – as int
Returns:(Options) this Options
psm(PSM psm)
set this PSM.
see PSM
Parameters:psm – as enum constant
Returns:(Options) this Options
resetPSM()
Sets this PSM to -1.

This causes Tess4J not to set the PSM at all.
Only use it, if you know what you are doing.
Returns:(Options) this Options
asLine()
Configure Options to recognize a single line.
Returns:(Options) this Options
asWord()
Configure Options to recognize a single word.
Returns:(Options) this Options
asChar()
Configure Options to recognize a single character.
Returns:(Options) this Options

Handle languages

language()
get the cutrrent language
Returns:(String) the language short string
language(String language)
Set the language short string.
(must not be null or empty,
see Settings.OcrLanguage() for a useable fallback)
According to the Tesseract rules this is a 3-lowercase-letters string
like eng, deu, fra, rus, ….
For special cases it might be something like xxx_yyy (chi_sim)
or even xxx_yyyy (deu_frak) or even xxx_yyy_zzzz (chi_tra_vert), but always all lowercase.
Take care that you have the corresponding ….traineddata file in the datapath/tessdata folder
latest at time of OCR feature usage
Parameters:language – the language string
Returns:(Options) this Options

Handle datapath

dataPath()
get the current datapath in this Options.
might be null, if no OCR feature was used until now
if null, it will be evaluated at time of OCR feature usage to the default
SikuliX path or to Settings.OcrDataPath (if set)
Returns:(String) the current Tesseract datapath in this Options
dataPath(String dataPath)
Set folder for Tesseract to find language and configs files.
in the tessdata subfolder (the path spec might be given without the trailing /tessdata)
TAKE CARE, that all is in place at time of OCR feature usage
if null, it will be evaluated at time of OCR feature usage to the default
SikuliX path or to Settings.OcrDataPath (if set)
Parameters:dataPath – the absolute filename string
Returns:(Options) this Options

Handle the pre-OCR image optimization

smallFont()
Convenience: Configure the Option’s optimization.

Might give better results in cases with small
fonts with a pixel height lt 12 (font sizes lt 10)
Returns:(Options) this Options
textHeight()
current base for image optimization before OCR.
Returns:(float) value
textHeight(float height)
Configure image optimization.

should be the (in case average) height in pixels of an uppercase X in the image’s text
NOTE: should only be tried in cases, where the defaults do not lead to acceptable results
Parameters:height – a number of pixels
Returns:(Options) this Options
fontSize(int size)
Configure the image optimization.

should be the (in case average) fontsize as base for internally calculating the OCR.Options.textHeight()
NOTE: should only be tried in cases, where the defaults do not lead to acceptable results
Parameters:size – of a font
Returns:(Options) this Options

Handle Tesseract variables

variables()
Returns:(Map<String, String>) the currently stored variables
variable(String key, String value)
set a variable for Tesseract.

you should know, what you are doing - consult the Tesseract docs
Parameters:
  • key – the key
  • value – the value
Returns:

(Options) this Options

Handle Tesseract configs

configs()
get current configs
Returns:(List<String>) currently stored names of configs files
configs(String... configs)
set one ore more configs file names.
you should know, what you are doing - consult the Tesseract docs
Parameters:configs – one or more configs filenames
Returns:(Options) this Options
configs(List<String> configs)
set a list of configs file names.
you should know, what you are doing - consult the Tesseract docs
Parameters:configs – a list of configs filenames
Returns:(Options) this Options

to be written