Features Overview

This page introduces the library’s recognition API and the capabilities covered in depth elsewhere in this guide. AsposeOcr is the entry point for the entire library. Its Recognize() method accepts an OcrInput and returns an OcrOutput — a list of RecognitionResult, one per image or PDF page.

Single-Image and PDF Recognition

OcrInput is constructed with an InputType — InputType.SingleImage for a raster image, or InputType.PDF for a PDF document. Files are queued with OcrInput.Add(). Disposing OcrInput only clears the queued file paths it holds.

using Aspose.OCR;

var api = new AsposeOcr();
using var input = new OcrInput(InputType.PDF);
input.Add("document.pdf");
OcrOutput output = api.Recognize(input);

Recognition Results

Each RecognitionResult exposes RecognitionText (the full recognized page text) and RecognitionLinesResult (a list of RecognitionResult.LinesResult, each with TextInLine and a System.Drawing.Rectangle bounding box in Line).

foreach (RecognitionResult page in output)
{
    Console.WriteLine(page.RecognitionText);
    foreach (RecognitionResult.LinesResult line in page.RecognitionLinesResult)
    {
        Console.WriteLine($"{line.Line}: {line.TextInLine}");
    }
}

Batch Processing

OcrInput accepts more than one file of the same input type. OcrOutput preserves the order the files were added in, with one RecognitionResult per file (or per PDF page).

using var input = new OcrInput(InputType.SingleImage);
input.Add("page-1.jpg");
input.Add("page-2.png");
OcrOutput output = api.Recognize(input);

Tips and Best Practices

Dispose OcrInput (or wrap it in a using statement) once recognition is complete to release the underlying resources.
Only InputType.SingleImage and InputType.PDF are supported — any other input type throws NotSupportedException.
Recognition is Latin-script only; there is no language-selection parameter.
PDF pages are rendered internally before recognition, so no separate PDF-to-image conversion step is needed.

Common Issues

Issue	Cause	Fix
`NotSupportedException` on `Recognize()`	An `OcrInput` was constructed with an unsupported `InputType`	Use only `InputType.SingleImage` or `InputType.PDF`
`FileNotFoundException` on `Recognize()`	A path added via `OcrInput.Add()` does not exist	Verify the file path before calling `Add()`
Empty `RecognitionLinesResult`	No text line was detected in that image or page	Confirm the source image contains legible, non-rotated Latin-script text

FAQ

What languages does Aspose.OCR FOSS for .NET recognize?

Latin-script text. The embedded recognition model does not cover non-Latin scripts.

Does it require an internet connection?

No. All three ONNX models (detection, refinement, recognition) are embedded in the assembly and run locally through Microsoft.ML.OnnxRuntime.

Can I recognize multiple files in one call?

Yes — add multiple files to the same OcrInput before calling AsposeOcr.Recognize(). The returned OcrOutput preserves their order.

What platforms does this run on?

It targets .NET Standard 2.0, .NET Framework 4.8, and .NET 8.0+. Image processing requires Windows, because it depends on System.Drawing.Common.

API Reference Summary

Class/Method	Description
`AsposeOcr.Recognize(OcrInput)`	Entry point: recognizes text and returns an `OcrOutput`
`OcrInput.Add(string)`	Queues a file path for recognition
`InputType`	Enum: `SingleImage` or `PDF`
`RecognitionResult.RecognitionText`	Full recognized page text
`RecognitionResult.RecognitionLinesResult`	List of recognized lines with bounding boxes
`RecognitionResult.LinesResult.TextInLine`	Recognized text for one line
`RecognitionResult.LinesResult.Line`	Pixel-coordinate bounding box for one line

Features Overview