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LoadAsync(Stream,LeadRect,int,CodecsLoadByteOrder,int,int,object) Method

Summary

Loads the specified rectangle from the specified image stream using the specified options asynchronously.

Syntax
C#
VB
Java
Objective-C
C++
public RasterImage LoadAsync( 
   Stream stream, 
   LeadRect tile, 
   int bitsPerPixel, 
   CodecsLoadByteOrder order, 
   int firstPage, 
   int lastPage, 
   object userState 
) 
Public Overloads Function LoadAsync( _ 
   ByVal stream As Stream, _ 
   ByVal tile As LeadRect, _ 
   ByVal bitsPerPixel As Integer, _ 
   ByVal order As CodecsLoadByteOrder, _ 
   ByVal firstPage As Integer, _ 
   ByVal lastPage As Integer, _ 
   ByVal userState As Object _ 
) As RasterImage 
- (void)loadStreamAsync:(LTLeadStream *)stream  
                   tile:(LeadRect)tile  
           bitsPerPixel:(NSInteger)bitsPerPixel  
                  order:(LTCodecsLoadByteOrder)order  
              firstPage:(NSInteger)firstPage  
               lastPage:(NSInteger)lastPage  
             completion:(void (^)(LTRasterImage * __nullable image, NSError * __nullable error))completion 
public Object loadAsync(ILeadStream stream, LeadRect tile, int bitsPerPixel, CodecsLoadByteOrder order, int firstPage, int lastPage, Object userState) 
public: 
RasterImage^ LoadAsync(  
   Stream^ stream, 
   LeadRect tile, 
   int bitsPerPixel, 
   CodecsLoadByteOrder order, 
   int firstPage, 
   int lastPage, 
   Object^ userState 
)  

Parameters

stream
A Stream containing the image data to load.

tile
A LeadRect describing the tile/area of the image to load.

bitsPerPixel
Resulting image pixel depth.

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.

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 support this type/member is not used. Instead, refer to RasterCodecs Async Operations.

This method loads a section of an image file (any format). The section begins is defined by tile rectangle.

Valid values for the bitsPerPixel parameter 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.

Valid values for the order parameter are:

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.

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 Image 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.

The RasterCodecs class supports loading image files asynchronously using the LoadAsync methods. When calling any of these methods, the caller's 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
C#
VB
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
using LeadtoolsExamples.Common; 
 
public void LoadAsyncStream4Example() 
{ 
   RasterCodecs codecs = new RasterCodecs(); 
 
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp"); 
 
   // Load a random tile from the image at 1 bits/pixel asynchronously 
   LeadRect tileRect = new LeadRect(100, 50, 200, 150); 
   codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncStream4Example_LoadAsyncCompleted); 
   Stream stream = File.OpenRead(srcFileName); 
   object rasterImageObject = codecs.LoadAsync(stream, tileRect, 1, CodecsLoadByteOrder.Rgb, 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 LoadAsyncStream4Example_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 loaded OK, size: {0} by {1}, order: {2}, bits/pixel: {3}", image.Width, image.Height, image.Order, image.BitsPerPixel); 
      image.Dispose(); 
   } 
 
   // We should close the stream here 
   e.Stream.Dispose(); 
 
   // Unsubscribe to the event and dispose the RasterCodecs object 
   RasterCodecs codecs = sender as RasterCodecs; 
   codecs.LoadAsyncCompleted -= new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncStream4Example_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 LoadAsyncStream4Example() 
   Dim codecs As New RasterCodecs() 
 
   Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp") 
 
   ' Load a random tile from the image at 1 bits/pixel asynchronously 
   Dim tileRect As New LeadRect(100, 50, 200, 150) 
   AddHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncStream4Example_LoadAsyncCompleted 
   Dim stream As Stream = File.OpenRead(srcFileName) 
   Dim rasterImageObject As Object = codecs.LoadAsync(stream, tileRect, 1, CodecsLoadByteOrder.Rgb, 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 LoadAsyncStream4Example_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 loaded OK, size: {0} by {1}, order: {2}, bits/pixel: {3}", image.Width, image.Height, image.Order, image.BitsPerPixel) 
      image.Dispose() 
   End If 
 
   ' We should close the stream here 
   e.Stream.Dispose() 
 
   ' Unsubscribe to the event and dispose the RasterCodecs object 
   Dim codecs As RasterCodecs = DirectCast(sender, RasterCodecs) 
   RemoveHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncStream4Example_LoadAsyncCompleted 
   codecs.Dispose() 
End Sub 
 
Public NotInheritable Class LEAD_VARS 
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images" 
End Class 

Requirements

Target Platforms

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Leadtools.Codecs Assembly