RasterImageTypeConverter Class

This class derives from the standard .NET TypeConverter class to provides functionality for converting RasterImage objects from other data types.

The following data types are supported:

• Uri containing the URL to the image file with optional parameters.
• String containing the path to the image file with optional parameters.
• Stream containing the data of the image file.
• An array of Byte containing the data of the image file.

The CanConvertFrom method will return true if any of the supported object types is passed into the sourceType parameter. However, this does not mean that the conversion operation will succeed, this depends on whether the data contains a valid image that LEADTOOLS can load.

The ConvertFrom method will try to convert the object passed into the value parameter to a valid RasterImage object.

For Uri and String source objects, LEADTOOLS supports optional extra parameters passed as standard HTML query string to fine tune the loading of RasterImage objects. The following table lists these parameters:

All these parameters are optional and should be passed as a standard HTML query string. The order is not important. Here are a few examples of valid strings:

            // Load all the pages in the TIF file hosted at an HTTP URL
            http://tempuri.org/MyImage.tif
            // Load the first page only of the multi-page TIF file hosted at an HTTP URL
            http://tempuri.org/MyImage.tif?LeadFirstPage=1&LeadLastPage=1
            // Load the second and third page of the multi-page TIF file hosted at an HTTP URL as 24 bits/pixel with RGB color order
            http://tempuri.org/MyImage.tif?LeadBitsPerPixel=24&LeadOrder=Rgb&LeadFirstPage=2&LeadLastPage=3
            // Load all the pages in the TIF file hosted at an FTP site
            ftp://tempuri.org/MyImage.tif
            // Load all the pages in the TIF file in a disk file
            C:\Dir\MyImage.tif
            file:://C:/Dir/MyImage.tif
            file:://myserver/MyImage.tif
            // Load the second and third page of the multi-page TIF file in a disk file as 24 bits/pixel with RGB color order
            C:\Dir\MyImage\MyImage.tif?LeadBitsPerPixel=24&LeadOrder=Rgb&LeadFirstPage=2&LeadLastPage=3
            

            // Load all the pages in the TIF file set as resource
            "MyImage.tif"
            // Load the first page only of the multi-page TIF file set as a resource
            "MyImage.tif?LeadFirstPage=1&LeadLastPage=1"
            // Load the second and third page of the multi-page TIF file set as a resource as 24 bits/pixel with RGB color order
            "MyImage.tif?LeadBitsPerPixel=24&LeadOrder=Rgb&LeadFirstPage=2&LeadLastPage=3"
            // Load the second and third page of the multi-page TIF file set as a resource as 24 bits/pixel with RGB color order
            "MyImage.tif?LeadBitsPerPixel=24&LeadOrder=Rgb&LeadFirstPage=2&LeadLastPage=3"
            // Silverlight only: Load the image and set it as a WriteableBitmap in a RasterImage
            "MyImage.tif?LeadUseWriteableBitmap=True"
            // Silverlight only: Load the PNG image using Silverlight and set it as a WriteableBitmap in a RasterImage
            "MyImage.tif?LeadUseWriteableBitmap=True&LeadUseNativeLoad=True"
            

Query string are not supported for String and an array of Byte data types.

The LEADTOOLS WPF and Silverlight controls use the RasterImageTypeConverter to load a RasterImage from a XAML file.

The image returned from the ConvertFrom method will have itsRasterImage.IsLoading property set to true since this method will load the image asynchronously. To get notified when the image has finished loading, create the RasterImageTypeConverter with your own RasterCodecs instance and subscribe to the RasterCodecs.LoadAsyncCompleted event before calling ConvertFrom as show in the example below.

This example will use the RasterImageTypeConverter to load an image from a URL.

• C#
• Visual Basic
• WinRT C#
• WinRT JavaScript
• Silverlight C#
• Silverlight VB

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Imports Leadtools
Imports Leadtools.Codecs
Imports Leadtools.ImageProcessing
Imports Leadtools.ImageProcessing.Color

      
Public Sub RasterImageTypeConverterExample()
   Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Ocr1.tif")
   ' Construct the source URL to use the source file and load the image
   Dim uri As New Uri(srcFileName)

   Dim codecs As New RasterCodecs()

   ' Create a new instance of the RasterImageTypeConverter class
   Dim rasterImageConverter As New RasterImageTypeConverter(codecs)

   ' We should be able to convert from a URL
   Debug.Assert(rasterImageConverter.CanConvertFrom(uri.GetType()))

   ' Convert the image

   ' The return value from RasterImageTypeConverter.ConvertFrom might be an image that is
   ' still loading. So, we must subscribe to the RasterCodecs.LoadAsyncCompleteted
   ' event to obtain the finished image
   AddHandler codecs.LoadAsyncCompleted, AddressOf rasterImageTypeConverterExample_LoadAsyncCompleted
   Dim rasterImageObject As Object = rasterImageConverter.ConvertFrom(uri)

   ' Notice that the returned rasterImageObject is a RasterImage with IsLoading set to true at this point
   ' The IsLoading will be false (and hence, the object will be usable) when the LoadAsyncCompleteted
   ' fires.
End Sub

Private Sub rasterImageTypeConverterExample_LoadAsyncCompleted(ByVal sender As Object, ByVal e As CodecsLoadAsyncCompletedEventArgs)
   ' Check if the user canceled or if we have errors
   If e.Cancelled Then
      Console.WriteLine("Canceled by the user")
   ElseIf Not IsNothing(e.Error) Then
      Console.WriteLine("Error: " + e.Error.Message)
   Else
      ' Everything is OK, get the image
      Dim image As RasterImage = e.Image

      Console.WriteLine("Image at {0} loaded OK, size: {1} by {2}", e.Uri, image.Width, image.Height)

      image.Dispose()
   End If

   ' Unsubscribe to the event and dispose the RasterCodecs object
   Dim codecs As RasterCodecs = DirectCast(sender, RasterCodecs)
   RemoveHandler codecs.LoadAsyncCompleted, AddressOf rasterImageTypeConverterExample_LoadAsyncCompleted
   codecs.Dispose()
End Sub

Public NotInheritable Class LEAD_VARS
Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images"
End Class

using Leadtools;
using Leadtools.Codecs;

      
public void RasterImageTypeConverterExample()
{
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Ocr1.tif");
   // Construct the source URL to use the source file and load the image
   Uri uri = new Uri(srcFileName);

   RasterCodecs codecs = new RasterCodecs();

   // Create a new instance of the RasterImageTypeConverter class
   RasterImageTypeConverter rasterImageConverter = new RasterImageTypeConverter(codecs);

   // We should be able to convert from a URL
   Debug.Assert(rasterImageConverter.CanConvertFrom(uri.GetType()));

   // Convert the image

   // The return value from RasterImageTypeConverter.ConvertFrom might be an image that is
   // still loading. So, we must subscribe to the RasterCodecs.LoadAsyncCompleteted
   // event to obtain the finished image
   codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(rasterImageTypeConverterExample_LoadAsyncCompleted);
   object rasterImageObject = rasterImageConverter.ConvertFrom(uri);

   // Notice that the returned rasterImageObject is a RasterImage with IsLoading set to true at this point
   // The IsLoading will be false (and hence, the object will be usable) when the LoadAsyncCompleteted
   // fires.
}

private void rasterImageTypeConverterExample_LoadAsyncCompleted(object sender, CodecsLoadAsyncCompletedEventArgs e)
{
   // Check if the user canceled or if we have errors
   if (e.Cancelled)
   {
      Console.WriteLine("Canceled by the user");
   }
   else if (e.Error != null)
   {
      Console.WriteLine("Error: " + e.Error.Message);
   }
   else
   {
      // Everything is OK, get the image
      RasterImage image = e.Image;

      Console.WriteLine("Image at {0} loaded OK, size: {1} by {2}", e.Uri, image.Width, image.Height);

      image.Dispose();
   }

   // Unsubscribe to the event and dispose the RasterCodecs object
   RasterCodecs codecs = sender as RasterCodecs;
   codecs.LoadAsyncCompleted -= new EventHandler<CodecsLoadAsyncCompletedEventArgs>(rasterImageTypeConverterExample_LoadAsyncCompleted);
   codecs.Dispose();
}

static class LEAD_VARS
{
public const string ImagesDir = @"C:\Users\Public\Documents\LEADTOOLS Images";
}

Target Platforms

Reference

RasterImageTypeConverter Members
Leadtools.Codecs Namespace