Crop Regions and Rectangles with IronOCR

January 19, 2022

Updated June 1, 2025

How do I set content areas on PDFs with IronOCR?

ContentAreas and PDFs

OcrInput.LoadPdf and LoadPdfPage methods all have the option to add a ContentArea.

The question - How do I know how big my content area is as PDFs are not sized in pixels, but content areas are generally measured in them?

Option 1

OcrInput.TargetDPI default is 225 - this dictates the size of the PDF image in pixels. IronOCR will read this.

Option 2 (ideal use case)

Use OcrInput.LoadPdf() with your PDF template.
Use OcrInput.GetPages() to get the input's width and height.
Use OcrInput.GetPages().First().ToBitmap() to get the exact image the OCR engine will read.
You can now measure ContentAreas in pixels from the exported image.
The targeted coordinates could be used for a specific OCR region (see in Final Result).

To get your info:

using System.Linq;  // Needed for First()
using IronOcr;

var ocr = new IronTesseract();
using (var input = new OcrInput())
{
    // Load the PDF document
    input.LoadPdf("example.pdf");

    // Save the first page as a bitmap to measure it
    input.GetPages().First().ToBitmap().SaveAs("measure-me.bmp");

    // Get the dimensions of the first page
    var width = input.GetPages().First().Width;
    var height = input.GetPages().First().Height;

    // Optionally, output the dimensions to understand the scale
    Console.WriteLine($"Width: {width}px, Height: {height}px");
}

using System.Linq;  // Needed for First()
using IronOcr;

var ocr = new IronTesseract();
using (var input = new OcrInput())
{
    // Load the PDF document
    input.LoadPdf("example.pdf");

    // Save the first page as a bitmap to measure it
    input.GetPages().First().ToBitmap().SaveAs("measure-me.bmp");

    // Get the dimensions of the first page
    var width = input.GetPages().First().Width;
    var height = input.GetPages().First().Height;

    // Optionally, output the dimensions to understand the scale
    Console.WriteLine($"Width: {width}px, Height: {height}px");
}

Imports System.Linq ' Needed for First()
Imports IronOcr

Private ocr = New IronTesseract()
Using input = New OcrInput()
	' Load the PDF document
	input.LoadPdf("example.pdf")

	' Save the first page as a bitmap to measure it
	input.GetPages().First().ToBitmap().SaveAs("measure-me.bmp")

	' Get the dimensions of the first page
	Dim width = input.GetPages().First().Width
	Dim height = input.GetPages().First().Height

	' Optionally, output the dimensions to understand the scale
	Console.WriteLine($"Width: {width}px, Height: {height}px")
End Using

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Final Result:

using IronOcr;
using IronSoftware.Drawing; // Needed for Rectangle

var ocr = new IronTesseract();
using (var input = new OcrInput())
{
    // Define the content area rectangle with specific pixel coordinates
    var contentArea = new Rectangle
    { 
        X = 215, 
        Y = 1250, 
        Height = 280, 
        Width = 1335 
    };  //<-- the area you want in px

    // Load the specific content area of the PDF
    input.LoadPdf("example.pdf", contentArea: contentArea);

    // Perform OCR on the defined content area
    var result = ocr.Read(input);

    // Optionally, print the OCR result
    Console.WriteLine(result.Text);
}

using IronOcr;
using IronSoftware.Drawing; // Needed for Rectangle

var ocr = new IronTesseract();
using (var input = new OcrInput())
{
    // Define the content area rectangle with specific pixel coordinates
    var contentArea = new Rectangle
    { 
        X = 215, 
        Y = 1250, 
        Height = 280, 
        Width = 1335 
    };  //<-- the area you want in px

    // Load the specific content area of the PDF
    input.LoadPdf("example.pdf", contentArea: contentArea);

    // Perform OCR on the defined content area
    var result = ocr.Read(input);

    // Optionally, print the OCR result
    Console.WriteLine(result.Text);
}

Imports IronOcr
Imports IronSoftware.Drawing ' Needed for Rectangle

Private ocr = New IronTesseract()
Using input = New OcrInput()
	' Define the content area rectangle with specific pixel coordinates
	Dim contentArea = New Rectangle With {
		.X = 215,
		.Y = 1250,
		.Height = 280,
		.Width = 1335
	}

	' Load the specific content area of the PDF
	input.LoadPdf("example.pdf", contentArea:= contentArea)

	' Perform OCR on the defined content area
	Dim result = ocr.Read(input)

	' Optionally, print the OCR result
	Console.WriteLine(result.Text)
End Using

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API Reference: OcrInput | OcrInput.Page