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

Summary

Loads the specified image stream using specific options asynchronously.

Syntax

C#
VB
Java
Objective-C
C++
public RasterImage LoadAsync( 
   Stream stream, 
   int bitsPerPixel, 
   CodecsLoadByteOrder order, 
   int firstPage, 
   int lastPage, 
   object userState 
) 
Public Overloads Function LoadAsync( _ 
   ByVal stream As Stream, _ 
   ByVal bitsPerPixel As Integer, _ 
   ByVal order As Leadtools.Codecs.CodecsLoadByteOrder, _ 
   ByVal firstPage As Integer, _ 
   ByVal lastPage As Integer, _ 
   ByVal userState As Object _ 
) As Leadtools.RasterImage 
- (void)loadStreamAsync:(LTLeadStream *)stream  
           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, int bitsPerPixel, CodecsLoadByteOrder order, int firstPage, int lastPage, Object userState) 

Parameters

stream
A Stream containing the image data to load.

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 stream.

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.

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 theRasterImage.IsLoading property to determine whether the image is finished loaded. Instead, subscribe to the LoadAsyncCompleted event to get notification when the LoadAsync operation is 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 LoadAsyncStream2Example() 
{ 
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Ocr1.tif"); 
 
   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>(LoadAsyncStream2Example_LoadAsyncCompleted); 
   Stream stream = File.OpenRead(srcFileName); 
   object rasterImageObject = codecs.LoadAsync(stream, 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 LoadAsyncStream2Example_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 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>(LoadAsyncStream2Example_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 LoadAsyncStream2Example() 
   Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Ocr1.tif") 
 
   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 LoadAsyncStream2Example_LoadAsyncCompleted 
   Dim stream As Stream = File.OpenRead(srcFileName) 
   Dim rasterImageObject As Object = codecs.LoadAsync(stream, 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 LoadAsyncStream2Example_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 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 LoadAsyncStream2Example_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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