How to Detect Page Rotation

Determining page rotation involves identifying the degree of rotation applied to a page within a document. This process specifically determine if the page has been rotated clockwise or counterclockwise by angles of 0, 90, 180, and 270 degrees. This information is crucial for rendering or processing the document accurately, ensuring that pages are displayed or printed in their correct orientations.

IronOCR takes page rotation detection to the next level. Once rotation has been detected, the returned value can be used in combination with the Rotate method to adjust the image to the correct orientation.

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First Step:

How to Detect Page Rotation

Download a C# library to detect page rotation
Import the PDF document and images for reading
Use the DetectPageOrientation method to detect rotation for all pages
Access the RotationAngle property to correct page rotation
Access the HighConfidence property to handle edge cases

Detect Page Rotation Example

After loading the document, you can utilize the DetectPageOrientation method to identify the rotation of each page. This method supports degrees of 0, 90, 180, and 270. For skewed images, the Deskew image correction method can be used. Subsequently, rotate the image back to its original orientation using the degree returned from the function. Let's proceed with a sample PDF.

Please note

This function performs well when the document is text-dense.

:path=/static-assets/ocr/content-code-examples/how-to/detect-page-rotation-detect-page-rotation.cs

using IronOcr;
using System;

using var input = new OcrInput();

// Load PDF document
input.LoadPdf("Clockwise90.pdf");

// Detect page rotation
var results = input.DetectPageOrientation();

// Ouput result
foreach(var result in results)
{
    Console.WriteLine(result.PageNumber);
    Console.WriteLine(result.HighConfidence);
    Console.WriteLine(result.RotationAngle);
}

Imports IronOcr
Imports System

Private input = New OcrInput()

' Load PDF document
input.LoadPdf("Clockwise90.pdf")

' Detect page rotation
Dim results = input.DetectPageOrientation()

' Ouput result
For Each result In results
	Console.WriteLine(result.PageNumber)
	Console.WriteLine(result.HighConfidence)
	Console.WriteLine(result.RotationAngle)
Next result

VB C#

Understanding the Result

PageNumber: Indicates the zero-based index of the page.
RotationAngle: Provides the corrective rotation angle in degrees. This angle can be applied to the Rotate method to return the image to right-side-up rotation. For example, if the image is rotated 90 degrees clockwise, the angle returned will be 270, which can then be passed to the Rotate method as input.Rotate(RotationAngle).
HighConfidence: Indicates the level of confidence in the orientation result.

Chaknith Bin

Software Engineer

Chaknith is the Sherlock Holmes of developers. It first occurred to him he might have a future in software engineering, when he was doing code challenges for fun. His focus is on IronXL and IronBarcode, but he takes pride in helping customers with every product. Chaknith leverages his knowledge from talking directly with customers, to help further improve the products themselves. His anecdotal feedback goes beyond Jira tickets and supports product development, documentation and marketing, to improve customer’s overall experience.When he isn’t in the office, he can be found learning about machine learning, coding and hiking.