Google WindowsPhone 8.1 Optical Character Recognition(OCR) Library :Read Text from Images (C#-XAML) | SubramanyamRaju Xamarin & Windows App Dev Tutorials

Thursday, 21 August 2014

WindowsPhone 8.1 Optical Character Recognition(OCR) Library :Read Text from Images (C#-XAML)

1.Introduction:

Wow! the most wanted library is now supported for windowsphone 8.1.lot of developers waiting for this library,And finally it was released by Microsoft in last "Preview Program".Optical Character Recognition(OCR) library is helpful to read text from images and returns the text and layout information . 
OCR library features:
  • Ability to recognize patterns (Ex: email,phone,URI's) from Image text
  • Launching Above patterns(Ex:Making Phone Call,Sending Mail,Visit Website)
OCR Limitations:
  • Image dimension should be  >= 40*40 pixels and <= 2600*2600 pixels
  • Image text lines must have written in same orientations and same directions.Fortunately OCR can able to correct rotation up to ±40 degrees.
An inaccurate reading may be caused by the following:
  • Blurry images
  • Handwritten or cursive text
  • Artistic font styles
  • Small text size (less than 15 pixels for Western languages, or less than 20 pixels for East Asian languages)
  • Complex backgrounds
  • Shadows or glare over text
  • Perspective distortion
  • Oversized or dropped capital letters at the beginnings of words
  • Subscript, superscript, or strike-through text and please read more from here

2.Building the sample:

  • Make sure you’ve downloaded and installed the Windows Phone SDK. For more information, see Get the SDK.
  • I assumes that you’re going to test your app on the Windows Phone emulator. If you want to test your app on a phone, you have to take some additional steps. For more info, see Register your Windows Phone device for development.
  • This post assumes you’re using Microsoft Visual Studio Express 2013 for Windows.

3.Download and install the OCR Library:

This library is not included in Windows Software Development Kit (SDK).And it is distributed as a NuGet package,so to install this library  right click on your project=>Click on "Manage NuGet Packages" =>Online=>and search for "Microsoft.Windows.Ocr."  => Click on "Install" button.See below image for your reference

"Any CPU" problem:

This library does not work on "AnyCPU" target platform, to change the build configuration of your project from AnyCPU to x86, x64, or ARM Right click on the Solution -> Click on Configuration Properties -> Configuration Manager and change the active solution platform to x86 (If you are using an emulator) or ARM (If you are using a Windows Phone device).

After you install the OCR library into your project, "OcrResources" folder will be add to your project which is having "MsOcrRes.orp" file

When you install the package, the file <solution_name>\packages\Microsoft.Windows.Ocr.1.0.0\OcrResources \MsOcrRes.orp is copied and injected into your project in the location <solution_name>\<project_name>\OcrResources\MsOcrRes.orp. This file is consumed by the OcrEngine object for text recognition in a specific language.

4.OCR supported languages:

There are 21 supported languages. Based on recognition accuracy and performance, supported languages are divided into three groups:
  • Excellent: Czech, Danish, Dutch, English, Finnish, French, German, Hungarian, Italian, Norwegian, Polish, Portuguese, Spanish and Swedish.
  • Very good: Chinese Simplified, Greek, Japanese, Russian and Turkish.
  • Good: Chinese Traditional and Korean.
Note:By default English language resources are included in the target project.If you want to use a custom group of languages in your app, use the OCR Resources Generator tool to generate a new OCR resources file, and replace the resources that were injected into your project when you installed the package

To generate OCR resource files

  • Launch the OCR Resources Generator tool located at <solution_name>\packages\Microsoft.Windows.Ocr.1.0.0\OcrResourcesGenerator\OcrResourcesGenerator.exe.And you would be found following dialog box


  • Use the buttons in the center of the tool to create a list of the required languages.
  • Click the Generate Resources button. Pick a location to save the new resources file.
  • Replace the existing file <solution_name>\<project_name>\OcrResources\MsOcrRes.orp with the new file that you just generated.

5.How to extract text from an image?

Step1:In page constructor, create and initialize a global instance of the OcrEngine. Also declare two unsigned integer variables to store the width and height of the image.

Step2:Load the your image,convert it to WriteableBitmap to get image pixels height and width

Step3:Check image dimension should be  > 40*40 pixels and < 2600*2600 pixels

Step4:Call the RecognizeAsync method of the OcrEngine class. This method returns an OcrResult object, which contains the recognized text and its size and position. The result is split into lines, and the lines are split into words.

Step5:So after following above steps your code is like this for extract text from image.

C#

using System; 
using System.Collections.Generic; 
using System.IO; 
using System.Linq; 
using System.Runtime.InteropServices.WindowsRuntime; 
using System.Threading.Tasks; 
using Windows.Foundation; 
using Windows.Foundation.Collections; 
using Windows.Storage; 
using Windows.Storage.FileProperties; 
using Windows.UI; 
using Windows.UI.Xaml; 
using Windows.UI.Xaml.Controls; 
using Windows.UI.Xaml.Controls.Primitives; 
using Windows.UI.Xaml.Data; 
using Windows.UI.Xaml.Input; 
using Windows.UI.Xaml.Media; 
using Windows.UI.Xaml.Media.Imaging; 
using Windows.UI.Xaml.Navigation; 
using WindowsPreview.Media.Ocr; 
 
 
 
namespace OCRImgReadText 
{ 
    
    public sealed partial class MainPage : Page 
    { 
        // Bitmap holder of currently loaded image. 
        private WriteableBitmap bitmap; 
        // OCR engine instance used to extract text from images. 
        private OcrEngine ocrEngine; 
 
        public MainPage() 
        { 
            this.InitializeComponent(); 
            ocrEngine = new OcrEngine(OcrLanguage.English); 
            TextOverlay.Children.Clear(); 
        } 
 
         
        protected override async void OnNavigatedTo(NavigationEventArgs e) 
        { //Get local image
            var file = await Windows.ApplicationModel.Package.Current.InstalledLocation.GetFileAsync("TestImages\\SQuotes.jpg"); 
            await LoadImage(file); 
        } 
        private async Task LoadImage(StorageFile file) 
        { 
            ImageProperties imgProp = await file.Properties.GetImagePropertiesAsync(); 
 
            using (var imgStream = await file.OpenAsync(FileAccessMode.Read)) 
            { 
                bitmap = new WriteableBitmap((int)imgProp.Width, (int)imgProp.Height); 
                bitmap.SetSource(imgStream); 
                PreviewImage.Source = bitmap; 
            } 
        } 
        private async void ExtractText_Click(object sender, RoutedEventArgs e) 
        { 
            //// Prevent another OCR request, since only image can be processed at the time at same OCR engine instance. 
            //ExtractTextButton.IsEnabled = false; 
 
            // Check whether is loaded image supported for processing. 
            // Supported image dimensions are between 40 and 2600 pixels. 
            if (bitmap.PixelHeight < 40 || 
                bitmap.PixelHeight > 2600 || 
                bitmap.PixelWidth < 40 || 
                bitmap.PixelWidth > 2600) 
            { 
                ImageText.Text = "Image size is not supported." + 
                                    Environment.NewLine + 
                                    "Loaded image size is " + bitmap.PixelWidth + "x" + bitmap.PixelHeight + "." + 
                                    Environment.NewLine + 
                                    "Supported image dimensions are between 40 and 2600 pixels."; 
                //ImageText.Style = (Style)Application.Current.Resources["RedTextStyle"]; 
 
                 return; 
            } 
 
            // This main API call to extract text from image. 
            var ocrResult = await ocrEngine.RecognizeAsync((uint)bitmap.PixelHeight, (uint)bitmap.PixelWidth, bitmap.PixelBuffer.ToArray()); 
 
            // OCR result does not contain any lines, no text was recognized.  
            if (ocrResult.Lines != null) 
            { 
                // Used for text overlay. 
                // Prepare scale transform for words since image is not displayed in original format. 
                var scaleTrasform = new ScaleTransform 
                { 
                    CenterX = 0, 
                    CenterY = 0, 
                    ScaleX = PreviewImage.ActualWidth / bitmap.PixelWidth, 
                    ScaleY = PreviewImage.ActualHeight / bitmap.PixelHeight, 
                }; 
 
                if (ocrResult.TextAngle != null) 
                { 
                  
                    PreviewImage.RenderTransform = new RotateTransform 
                    { 
                        Angle = (double)ocrResult.TextAngle, 
                        CenterX = PreviewImage.ActualWidth / 2, 
                        CenterY = PreviewImage.ActualHeight / 2 
                    }; 
                } 
 
                string extractedText = ""; 
 
                // Iterate over recognized lines of text. 
                foreach (var line in ocrResult.Lines) 
                { 
                    // Iterate over words in line. 
                    foreach (var word in line.Words) 
                    { 
                        var originalRect = new Rect(word.Left, word.Top, word.Width, word.Height); 
                        var overlayRect = scaleTrasform.TransformBounds(originalRect); 
 
                        var wordTextBlock = new TextBlock() 
                        { 
                            Height = overlayRect.Height, 
                            Width = overlayRect.Width, 
                            FontSize = overlayRect.Height * 0.8, 
                            Text = word.Text, 
                           
                        }; 
 
                        // Define position, background, etc. 
                        var border = new Border() 
                        { 
                            Margin = new Thickness(overlayRect.Left, overlayRect.Top, 00), 
                            Height = overlayRect.Height, 
                            Width = overlayRect.Width, 
                            Background=new SolidColorBrush(Colors.Orange),Opacity=0.5,HorizontalAlignment=HorizontalAlignment.Left,VerticalAlignment=VerticalAlignment.Top, 
                            Child = wordTextBlock, 
                           
                        }; 
                        OverlayTextButton.IsEnabled = true; 
                        // Put the filled textblock in the results grid. 
                        TextOverlay.Children.Add(border); 
                        extractedText += word.Text + " "; 
                    } 
                    extractedText += Environment.NewLine; 
                } 
 
                ImageText.Text = extractedText; 
                
            } 
            else 
            { 
                ImageText.Text = "No text."; 
                
            } 
        } 
 
        private void OverlayText_Click(object sender, RoutedEventArgs e) 
        { 
            if(TextOverlay.Visibility==Visibility.Visible) 
            { 
                TextOverlay.Visibility = Visibility.Collapsed; 
            } 
            else 
            { 
                TextOverlay.Visibility = Visibility.Visible; 
            } 
        } 
    } 
} 
Step6:And your UI might be like this

XAML

<Grid        <Grid.RowDefinitions            <RowDefinition Height="Auto"/> 
            <RowDefinition Height="Auto"/> 
            <RowDefinition Height="*"/> 
        </Grid.RowDefinitions> 
        <StackPanel Grid.Row="1" x:Name="ControlPanel"  Orientation="Vertical"        <StackPanel   Orientation="Horizontal" Margin="10,0,10,0"                 <Button x:Name="ExtractTextButton" Content="Extract Image Text" FontSize="15" MinWidth="90" Click="ExtractText_Click"  Margin="0,0,5,0"/> 
                <Button x:Name="OverlayTextButton" IsEnabled="False" Content="Overlay Image Text" FontSize="15" MinWidth="90" Click="OverlayText_Click"  Margin="0,0,5,0"/> 
            </StackPanel> 
        <StackPanel Grid.Row="1" Orientation="Horizontal"/> 
        </StackPanel> 
        <ScrollViewer Grid.Row="2" VerticalScrollMode="Auto" VerticalScrollBarVisibility="Auto" Margin="0, 10, 0, 0"            <!-- This StackPanel changes its Orientation depending on the available width of the window. --> 
            <StackPanel x:Name="Output" Margin="10,0,10,0" Orientation="Vertical" Visibility="Visible" 
                <StackPanel x:Name="Content" Orientation="Vertical" Visibility="Visible" 
                    <Grid x:Name="Image"                        <Image x:Name="PreviewImage" Margin="0,0,10,10"  Source="" Stretch="Uniform" Width="300" HorizontalAlignment="Left" VerticalAlignment="Top"/> 
                        <Grid x:Name="TextOverlay" Visibility="Collapsed" Margin="0,0,10,10"  HorizontalAlignment="Left" VerticalAlignment="Top"/> 
                     </Grid> 
 
                    <!-- This StackPanel contains all of the image properties output. --> 
                    <Grid x:Name="Result" HorizontalAlignment="Left" VerticalAlignment="Top"                        <Grid.RowDefinitions                            <RowDefinition Height="Auto"/> 
                            <RowDefinition Height="Auto"/> 
                        </Grid.RowDefinitions> 
                        <TextBlock Grid.Row="0" FontSize="25" Text="Extracted image text:" /> 
                        <TextBlock Name="ImageText" Grid.Row="1" Foreground="#FF1CD399" FontSize="25" Text="Text not yet extracted."/> 
 
                    </Grid> 
 
                </StackPanel> 
 
            </StackPanel> 
        </ScrollViewer> 
    </Grid>

6.Output:


WpOCRSample
Note:When you run this downloaded sample ,you will get following error ,So you must install OCR library from "Manage NuGet Packages" 

FeedBack Note:
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5 comments:

  1. i am doing my project in ocr.your article was really helpful.
    it extraacted the text.now if i want to find some specific word in extracted text specified in textbox.
    it highlights every occurence of that word in extracted text and also highlights in the image like overlay text but only specifed word not all aimge.please if you can help

    ReplyDelete
  2. Greeting,

    I am having exception @ ocrEngine.RecognizeAsync line i.e.

    A first chance exception of type 'System.ArgumentException' occurred in Unknown Module.
    WinRT information: Pixels array is too short for provided width and height.

    Can you help?

    Thanks & Regards

    ReplyDelete
  3. Can i create my own language library??

    ReplyDelete
  4. I'm not a developer, i always use the free online ocr to recognize and scan text from image.

    ReplyDelete
  5. Thank you for publishing such a good article.
    I tried to follow all given steps. But after replacing MsOcrRes.orp and changing debug option to x86 I am continuously seeing this error.
    Could not find SDK "Microsoft.VCLibs, Version=12.0".
    There is not much on google about this problem. Can you help me understanding this problem. I am using Visual Studio 2015.

    ReplyDelete

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