LoadAsync(Uri,int,CodecsLoadByteOrder,int,int,object) Method

Summary

Loads the specified image URL using specified options asynchronously.

Syntax

C++

public RasterImage LoadAsync( 
   Uri uri, 
   int bitsPerPixel, 
   CodecsLoadByteOrder order, 
   int firstPage, 
   int lastPage, 
   object userState 
)

Public Overloads Function LoadAsync( _ 
   ByVal uri As Uri, _ 
   ByVal bitsPerPixel As Integer, _ 
   ByVal order As CodecsLoadByteOrder, _ 
   ByVal firstPage As Integer, _ 
   ByVal lastPage As Integer, _ 
   ByVal userState As Object _ 
) As RasterImage

public: 
RasterImage^ LoadAsync(  
   Uri^ uri, 
   int bitsPerPixel, 
   CodecsLoadByteOrder order, 
   int firstPage, 
   int lastPage, 
   Object^ userState 
)

Parameters

uri
The Uri containing the input image data.

bitsPerPixel
Resulting image pixel depth. Valid values are:

Value	Meaning
0	Keep the original file's pixel depth (Do not convert).
1 to 8	The specified bits per pixel in the resulting image.
12	12 bits per pixel in the resulting image.
16	16 bits per pixel in the resulting image.
24	24 bits per pixel in the resulting image.
32	32 bits per pixel in the resulting image.
48	48 bits per pixel in the resulting image.
64	64 bits per pixel in the resulting image.

order
Color order for 16-bit, 24-bit, 32-bit, 48-bit, and 64-bit images. If the resulting image is less than 16 bits per pixel, this will have no effect since palletized images have no order. The following are valid values.

Value	Meaning
CodecsLoadByteOrder.Rgb	Red, green, and blue color order in memory
CodecsLoadByteOrder.Bgr	Blue, green, and red color order in memory
CodecsLoadByteOrder.Gray	12 or 16-bit grayscale image. 12 and 16-bit grayscale images are only supported in the Document/Medical Imaging editions.
CodecsLoadByteOrder.RgbOrGray	Load the image as red, green, blue OR as a 12 or 16-bit grayscale image. 12 and 16-bit grayscale images are supported in the Document/Medical Imaging editions
CodecsLoadByteOrder.BgrOrGray	Load the image as blue, green, red OR as a 12 or 16-bit grayscale image. 12 and 16-bit grayscale images are supported in the Document/Medical Imaging editions
CodecsLoadByteOrder.Romm	ROMM order. ROMM only supports 24 and 48-bit images
CodecsLoadByteOrder.BgrOrGrayOrRomm	Load the image as red, green, blue OR as a 12 or 16-bit grayscale image OR as ROMM. 12 and 16-bit grayscale images are supported in the Document/Medical Imaging editions only. ROMM only supports 24 and 48-bit color images.

firstPage
1-based index of the first page to load.

lastPage
The 1-based index of the last page to load. Must be greater than or equal to firstPage. You can pass -1 to load from firstPage to the last page in the file.

userState
A user-defined object that is passed to the method invoked when the asynchronous operation completes.

Return Value

The RasterImage object that this method loads. See remarks for the usage of this object.

Remarks

NOTE: This topic is part of RasterCodecs Async support using the .NET System.ComponentMode.AsyncOperation model. For .NET async/await, use Task<CodecsImageInfo> LoadAsync(ILeadStream stream, int bitsPerPixel, CodecsLoadByteOrder order, int firstPage, int lastPage).

The file can be in any supported image file format and bits per pixel, whether compressed or uncompressed.

This method will load all the pages in a multipage file. The resulting image will have the same bits/pixel and color order value of the image as it was stored in the file.

LEADTOOLS will attempt to load corrupted files so you can see at least a portion of the image. For these images, the load methods succeed, but LoadStatus will return an error code.

Use the CodecsLoadOptions class to set up other load option parameters before calling this method.

Support for 12 and 16-bit grayscale images is only available in the Document/Medical Imaging editions.

For supported formats, refer to Summary of All Supported File Formats.

LEADTOOLS loads all PDF files as Raster PDF uncompressed RasterImageFormat.RasPdf, regardless of the compression and color space used when saving the file.

LEADTOOLS supports the following URI schemes:

Scheme	Description
UriSchemeFile	Specifies that the URI is a disk file in local machine or universal naming convention (UNC) path.
UriSchemeHttp	Specifies that the URI is accessed through the Hypertext Transfer Protocol (HTTP).
UriSchemeHttps	Specifies that the URI is accessed through the Secure Hypertext Transfer Protocol (HTTPS).
UriSchemeFtp	Specifies that the URI is accessed through the File Transfer Protocol (FTP).

If uri points to a resource in a UriSchemeHttp, UriSchemeHttps or UriSchemeFtp, then this RasterCodecs will attempt to download image data in an iterative fashion by creating a temporary buffer. The size of this buffer can be determined and changed by setting up the UriOperationBufferSize prior to calling this method.

For authenticity and proxy settings, refer to UriOperationCredentials and UriOperationProxy.

The RasterCodecs class supports loading image files asynchronously using the LoadAsync methods. When calling any of these methods, the caller thread will not be blocked and the method will return instantly with an instance of RasterImage that is in a loading status (RasterImage.IsLoading set to true). You should not use the other properties of this object while the object is in loading status.

When the RasterCodecs object finishes loading the image, the various properties of the RasterImage will be populated with the image information and data and the RasterImage.IsLoading property will be set to false.

Do not poll the RasterImage.IsLoading property to determine whether the image has finished loading. Instead, subscribe to the LoadAsyncCompleted event to get notification when the LoadAsync operation has completed and whether any errors occurred.

The LoadAsyncCompleted event data will also contain the same object returned from LoadAsync so you do not have to keep the original object in your application.

Example

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
using LeadtoolsExamples.Common; 
 
public void LoadAsyncUrl1Example() 
{ 
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Ocr1.tif"); 
   Uri uri = new Uri(srcFileName); 
 
   RasterCodecs codecs = new RasterCodecs(); 
 
   // Now load the first page of the image as 24 bits/pixel with order BGR asynchronously 
   codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncUrl1Example_LoadAsyncCompleted); 
   object rasterImageObject = codecs.LoadAsync(uri, 24, CodecsLoadByteOrder.BgrOrGray, 1, 1, null); 
 
   // 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 LoadAsyncUrl1Example_LoadAsyncCompleted(object sender, CodecsLoadAsyncCompletedEventArgs e) 
{ 
   if (e.Cancelled) 
   { 
      Console.WriteLine("User canceled"); 
   } 
   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}, order: {3}, bits/pixel: {4}", e.Uri, image.Width, image.Height, image.Order, image.BitsPerPixel); 
      image.Dispose(); 
   } 
 
   // Unsubscribe to the event and dispose the RasterCodecs object 
   RasterCodecs codecs = sender as RasterCodecs; 
   codecs.LoadAsyncCompleted -= new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncUrl1Example_LoadAsyncCompleted); 
   codecs.Dispose(); 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\Users\Public\Documents\LEADTOOLS Images"; 
}

Imports Leadtools 
Imports Leadtools.Codecs 
Imports Leadtools.ImageProcessing 
Imports Leadtools.ImageProcessing.Color 
Imports Leadtools.Drawing 
Imports Leadtools.Svg 
 
Public Sub LoadAsyncUrl1Example() 
   Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Ocr1.tif") 
   Dim uri As New Uri(srcFileName) 
 
   Dim codecs As New RasterCodecs() 
 
   ' Now load the first page of the image as 24 bits/pixel with order BGR asynchronously 
   AddHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncUrl1Example_LoadAsyncCompleted 
   Dim rasterImageObject As Object = codecs.LoadAsync(uri, 24, CodecsLoadByteOrder.BgrOrGray, 1, 1, Nothing) 
 
   ' 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 LoadAsyncUrl1Example_LoadAsyncCompleted(ByVal sender As Object, ByVal e As CodecsLoadAsyncCompletedEventArgs) 
   If e.Cancelled Then 
      Console.WriteLine("User canceled") 
   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}, order: {3}, bits/pixel: {4}", e.Uri, image.Width, image.Height, image.Order, image.BitsPerPixel) 
      image.Dispose() 
   End If 
 
   ' Unsubscribe to the event and dispose the RasterCodecs object 
   Dim codecs As RasterCodecs = DirectCast(sender, RasterCodecs) 
   RemoveHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncUrl1Example_LoadAsyncCompleted 
   codecs.Dispose() 
End Sub 
 
Public NotInheritable Class LEAD_VARS 
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images" 
End Class