TesseractOcrEngine class
Namespace: PdfNetStack.Ocr.Tesseract
Assembly: PdfNetStack.Ocr.Tesseract.dll
Package: PdfNetStack
OCR with an installed Tesseract: each image is one tesseract process that reads the pixels
from its standard input and writes its results to its standard output, with no shell and no
temporary files. A process that crashes, hangs or floods its output only costs that image.
Safe to call from several threads, up to MaxConcurrentProcesses
at once. Tesseract and its language data are installed separately.
public sealed class TesseractOcrEngine : IOcrEngine, IDisposableInheritance
Implements
Examples
Section titled “Examples”using var engine = TesseractOcrEngine.Load(new TesseractOcrEngineOptions { Languages = ["fra+ara"] });
var report = new PdfOcr(engine, new PdfOcrOptions { Languages = ["fra+ara"] }).MakeSearchable(document);Properties
Section titled “Properties”InstalledLanguages
Section titled “ InstalledLanguages”The languages Tesseract has data for, as it names them.
public IReadOnlyCollection<string> InstalledLanguages { get; }Property Value
Section titled “Property Value”Version
Section titled “ Version”The version the executable reports, such as 5.5.0.
public string Version { get; }Property Value
Section titled “Property Value”Methods
Section titled “Methods”Dispose()
Section titled “ Dispose()”Refuses new calls, and ends those waiting for their turn with ObjectDisposedException.
A process already running is not stopped: its call finishes with its real result or failure,
within Timeout. To stop one sooner, cancel its token.
public void Dispose()Load(TesseractOcrEngineOptions?)
Section titled “ Load(TesseractOcrEngineOptions?)”Finds Tesseract, checks its version and that the data for Languages is there.
public static TesseractOcrEngine Load(TesseractOcrEngineOptions? options = null)Parameters
Section titled “Parameters”options TesseractOcrEngineOptions?
Where things are, and tuning; defaults when null.
Returns
Section titled “Returns”Exceptions
Section titled “Exceptions”The executable or the data for a language is missing. The message says where to get it.
TessdataPath does not exist.
A language name or a setting is not valid.
The executable fails, or is not Tesseract 4 or later.
Recognize(OcrBitmap, OcrRequest, CancellationToken)
Section titled “ Recognize(OcrBitmap, OcrRequest, CancellationToken)”Recognizes one upright 8 bit gray image; boxes come back in its pixel coordinates.
public OcrImageResult Recognize(OcrBitmap image, OcrRequest request, CancellationToken cancellationToken)Parameters
Section titled “Parameters”image OcrBitmap
The image, text upright.
request OcrRequest
The script to read.
cancellationToken CancellationToken
Stops the work between lines.
Returns
Section titled “Returns”Exceptions
Section titled “Exceptions”The language is not installed or not valid, or the image is larger than Tesseract reads.
The process took longer than Timeout and was killed.
The process failed, or its output cannot be used.
Cancelled; the process was killed.
The engine was disposed before this call’s process started.