Table of Contents

Class CommandOcrEngine

Namespace
Egami.Ocr
Assembly
Egami.dll

An IOcrEngine that runs an OCR program for each image and reads the hOCR or ALTO it writes, such as tesseract {image} {output} -l {langs} --dpi {dpi} hocr. Egami ships no engine and links none: the program is yours.

public sealed class CommandOcrEngine : IOcrEngine
Inheritance
CommandOcrEngine
Implements
Inherited Members

Examples

// Any OCR program that writes hOCR or ALTO is an engine. No shell runs the command, and each run has its own temp folder.
CommandOcrEngine tesseract = new("tesseract {image} {output} -l {langs} --dpi {dpi} hocr", new CommandOcrOptions
{
    Languages = ["eng"],
    Timeout = TimeSpan.FromMinutes(2),
});

try
{
    OcrResult result = await tesseract.RecognizeAsync(new OcrRequest(page), Ct);
    Console.WriteLine(result.Text);
}
catch (OcrEngineException e)
{
    Console.WriteLine($"{e.Message} {e.ErrorOutput}");
}

Remarks

The command is split into words at spaces, with double or single quotes around a word that holds spaces; no shell runs it, so file names and languages can never become commands. Each word may hold these placeholders: {image}, the path of the image as a PNG file; {output}, a path (without extension) for the program's output file; {langs}, the request's languages joined by +; {dpi}, the resolution as a whole number; {page}, the page index. Write {{ and }} for literal braces.

With {output} in the command, the engine reads that file, or the one file the program wrote beside it with an extension added (Tesseract adds .hocr or .xml); without it, the engine reads the program's standard output. Each run gets a temporary folder of its own that is deleted afterwards, so runs may overlap.

Constructors

CommandOcrEngine(string, CommandOcrOptions?)

Initializes a new instance of the CommandOcrEngine class.

public CommandOcrEngine(string command, CommandOcrOptions? options = null)

Parameters

command string

The program and its arguments, with placeholders, such as tesseract {image} - -l {langs} hocr.

options CommandOcrOptions

The options, or null for Default.

Examples

// Any OCR program that writes hOCR or ALTO is an engine. No shell runs the command, and each run has its own temp folder.
CommandOcrEngine tesseract = new("tesseract {image} {output} -l {langs} --dpi {dpi} hocr", new CommandOcrOptions
{
    Languages = ["eng"],
    Timeout = TimeSpan.FromMinutes(2),
});

try
{
    OcrResult result = await tesseract.RecognizeAsync(new OcrRequest(page), Ct);
    Console.WriteLine(result.Text);
}
catch (OcrEngineException e)
{
    Console.WriteLine($"{e.Message} {e.ErrorOutput}");
}

Exceptions

ArgumentNullException

command is null.

ArgumentException

The command is empty, has an unclosed quote, or names an unknown placeholder.

Properties

Info

Gets what the engine can do: its name, languages, largest image and whether calls may overlap.

public OcrEngineInfo Info { get; }

Property Value

OcrEngineInfo

Methods

RecognizeAsync(OcrRequest, CancellationToken)

Runs the program on the request's image and reads what it writes.

public Task<OcrResult> RecognizeAsync(OcrRequest request, CancellationToken cancellationToken = default)

Parameters

request OcrRequest

The image and how to read it.

cancellationToken CancellationToken

Cancels the run; the program is stopped.

Returns

Task<OcrResult>

The first page the program wrote, with ImageSize set to the image's size if the output gives none.

Exceptions

ArgumentNullException

request is null.

ArgumentException

The command uses {langs} and neither the request nor the options name a language.

OcrEngineException

The program could not start, failed, timed out or wrote no hOCR or ALTO.

OperationCanceledException

cancellationToken was canceled.

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