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StartFeedLoad(int,CodecsLoadByteOrder) Method

Summary

Initializes a file-load process in which you control the input stream.

Syntax
C#
VB
Java
Objective-C
C++
public void StartFeedLoad( 
   int bitsPerPixel, 
   CodecsLoadByteOrder order 
) 
Public Overloads Sub StartFeedLoad( _ 
   ByVal bitsPerPixel As Integer, _ 
   ByVal order As CodecsLoadByteOrder _ 
)  
- (BOOL)startFeedLoad:(NSInteger)bitsPerPixel order:(LTCodecsLoadByteOrder)order error:(NSError **)error 
public FeedCallbackThunk startFeedLoad(int bitsPerPixel, CodecsLoadByteOrder order) 
public: 
void StartFeedLoad(  
   int bitsPerPixel, 
   CodecsLoadByteOrder order 
)  

Parameters

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
The desired color order. Possible values 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.

Remarks

You must call the FeedLoad method to supply buffered data, and you must call StopFeedLoad when the loading is complete.

This file-load process is useful when receiving transmitted images, such as those on the Internet. It works the same way as the Load or LoadAsync methods, except that your code supplies the image data. The file-load process works as follows:

  1. You call the StartFeedLoad method to initialize the file-load process.
  2. You create a buffer, and each time you fill it with information, you call the FeedLoad method, which sends the data to the file-load process just as if the data were being read from a file on disk.
  3. Whenever it has enough data to do so, the file-load process behaves the same as in the Load or LoadAsync methods. It allocates and begins loading the image. It calls your LoadImage event handler, if one is specified, whenever it has enough data in its input buffer.

    The file-load process updates information in the RasterImage when it has received enough information to do so. The file-load process will make the first call to your event handler whenever this information is available.

  4. At any time after calling StartFeedLoad, you can call CancelFeedLoad to gracefully abort the feed load operation. This allows you to end the feed load process without throwing an exception.

  5. To end the file-load process, you call the StopFeedLoad method, which cleans up the process, and returns the loaded RasterImage, if successful. If you call this method before supplying the complete file, it will successfully clean up the process, but will throw an exception. You should catch the exception if the load is canceled purposely.

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

This method cannot be used in combination with StartRedirecting.

The CodecsLoadOptions.AllPages property controls whether RasterCodecs will try to load all pages or just the first page if the image data contains multiple pages.

Example

This example will use feed load to load an image from a url

C#
VB
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
using LeadtoolsExamples.Common; 
 
public void FeedLoadExample() 
{ 
   RasterCodecs codecs = new RasterCodecs(); 
 
   string url = @"https://www.leadtools.com/images/page_graphics/leadlogo.png"; 
   string destFileName = Path.Combine(LEAD_VARS.ImagesDir, "FeedLoad.bmp"); 
 
   // Create a WebRequest for the URL 
   WebRequest request = WebRequest.Create(url); 
   request.Proxy.Credentials = CredentialCache.DefaultCredentials; 
 
   // reduce the timeout to 20sec 
   request.Timeout = 20000; 
 
   WebResponse response = request.GetResponse(); 
   try 
   { 
      Stream strm = response.GetResponseStream(); 
 
      // Read chunks from the stream and feed load to the image 
      codecs.StartFeedLoad(0, CodecsLoadByteOrder.BgrOrGray); 
 
      const int bufferSize = 1024; 
      byte[] buffer = new byte[bufferSize]; 
 
      int read; 
 
      do 
      { 
         System.Windows.Forms.Application.DoEvents(); 
 
         read = strm.Read(buffer, 0, bufferSize); 
         Console.WriteLine("Downloading {0} bytes", read); 
         if (read > 0) 
            codecs.FeedLoad(buffer, 0, read); 
      } 
      while (read > 0); 
   } 
   finally 
   { 
      response.Close(); 
   } 
 
   RasterImage image = codecs.StopFeedLoad(); 
 
   // Save the image to disk 
   codecs.Save(image, destFileName, RasterImageFormat.Bmp, 24); 
   image.Dispose(); 
 
   // Clean up 
   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 FeedLoadExample() 
   Dim codecs As RasterCodecs = New RasterCodecs() 
 
   Dim url As String = "https://www.leadtools.com/images/web-header.jpg" 
   Dim destFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "FeedLoad.bmp") 
 
   ' Create a WebRequest for the URL 
   Dim request As WebRequest = WebRequest.Create(url) 
   request.Proxy.Credentials = CredentialCache.DefaultCredentials 
 
   ' reduce the timeout to 20sec 
   request.Timeout = 20000 
 
   Dim response As WebResponse = request.GetResponse() 
   Try 
      Dim strm As Stream = response.GetResponseStream() 
 
      ' Read chunks from the stream and feed load to the image 
      codecs.StartFeedLoad(0, CodecsLoadByteOrder.BgrOrGray) 
 
      Const bufferSize As Integer = 1024 
      Dim buffer(bufferSize - 1) As Byte 
 
      Dim read As Integer 
 
      Do 
         System.Windows.Forms.Application.DoEvents() 
 
         read = strm.Read(buffer, 0, bufferSize) 
         Console.WriteLine("Downloading {0} bytes", read) 
         If read > 0 Then 
            codecs.FeedLoad(buffer, 0, read) 
         End If 
      Loop While read > 0 
   Finally 
      response.Close() 
   End Try 
 
   Dim image As RasterImage = codecs.StopFeedLoad() 
 
   ' Save the image to disk 
   codecs.Save(image, destFileName, RasterImageFormat.Bmp, 24) 
   image.Dispose() 
 
   ' Clean up 
   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