OfficeIMO.Ocr.Tesseract 3.4.3

OfficeIMO.Ocr.Tesseract - Tesseract OCR provider

OfficeIMO.Ocr.Tesseract is an optional IOcrEngine backed by an installed Tesseract command-line executable. It does not bundle native binaries or trained language data.

Install

dotnet add package OfficeIMO.Ocr.Tesseract

Install Tesseract separately for the host operating system. TesseractOcrEngine.CreateDefault() discovers an explicit path, OFFICEIMO_TESSERACT_PATH, TESSERACT_PATH, the process PATH, and common platform locations:

TesseractOcrEngine engine = TesseractOcrEngine.CreateDefault();

You can verify the executable and required languages directly:

tesseract --version
tesseract --list-langs

Tesseract 5 is the current stable major line. Its command contract supports image input, language expressions, and TSV output; see the official Tesseract manual.

Recognize an image

using OfficeIMO.Ocr.Tesseract;
using OfficeIMO.Ocr;

TesseractOcrSession session = await TesseractOcr.CreateSessionAsync(new TesseractOcrSessionOptions {
    Languages = TesseractOcrLanguage.English | TesseractOcrLanguage.Polish,
    Engine = new TesseractOcrEngineOptions {
        PageSegmentationMode = 3,
        Timeout = TimeSpan.FromMinutes(1)
    }
});

OcrResult result = await session.RecognizeAsync(
    File.ReadAllBytes("scan.png"),
    "image/png",
    "scan.png");

foreach (OcrTextSpan span in result.Spans) {
    Console.WriteLine($"{span.Level}: {span.Text} ({span.Confidence:P0})");
}

session.Engine is the same neutral IOcrEngine accepted by OfficeIMO.Reader.Ocr, OfficeIMO.Pdf.Ocr, and future format integrations. The Tesseract package itself does not reference those packages.

The provider parses Tesseract TSV into line and word spans with pixel bounding boxes and normalized confidence. Tesseract TSV does not expose character boxes, so SupportsCharacterSpans is false. A process or delegate engine can still return character spans through the shared core contract.

GetVersionAsync() and GetLanguagesAsync() provide explicit installation evidence. TesseractLanguageData.EnsureAsync("eng+pol") can provision any model in the 28-language catalog, plus orientation data, into a versioned user cache. Downloads come from one immutable official tessdata_fast commit and must match package-pinned lengths and SHA-256 digests. Missing executables, unavailable trained data, unsupported input formats, and nonzero process exits surface as engine failures. A consuming format integration decides whether to stop or convert those failures into document diagnostics.

Per-request payload and output files use owner-only Unix directories and permissions. Temporary files are deleted by default; enable KeepTemporaryFiles only for controlled diagnostics.

Detect page orientation

The engine advertises SupportsOrientationDetection. Set OcrRequest.Operation to OcrOperation.DetectOrientation and run it through OcrEngineRunner to share the same timeout and concurrency rules as text recognition. The provider uses Tesseract's page segmentation mode 0 with osd trained data and returns OcrResult.Orientation.

ClockwiseRotationDegrees is the corrective rotation, restricted to 0, 90, 180, or 270 degrees. Confidence is Tesseract's orientation score divided by 15 and capped at 1; it is a provider-specific scale, not a probability. Missing data, insufficient text, or invalid/conflicting output produces a diagnostic and no accepted orientation. Callers choose their confidence threshold and retain the original image when evidence is insufficient. OfficeIMO.Pdf.Ocr exposes this through PdfOcrMergeOptions.DetectOrientation.

Targets and licenses

• Targets: netstandard2.0, net8.0, net10.0 (net472 is also included on Windows builds).
• OfficeIMO provider license: MIT.
• Tesseract is an external dependency distributed under its own Apache 2.0 license.

Dependency footprint

• External: An installed Tesseract CLI. Language data is not bundled; callers may use their system data or explicitly invoke the checksum-pinned provisioner.
• OfficeIMO: OfficeIMO.Ocr owns the neutral contracts. OfficeIMO.Ocr.Process supplies the bounded cross-platform process runner used by this provider.

See the complete OfficeIMO package map for related formats and conversion paths.