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StartFeedLoad(int,CodecsLoadByteOrder,int,int) Method

Summary

Initializes a file-load process in which you control the input stream with specific number of pages.

Syntax

C#
VB
Java
Objective-C
C++
public void StartFeedLoad( 
   int bitsPerPixel, 
   CodecsLoadByteOrder order, 
   int firstPage, 
   int lastPage 
) 

Public Overloads Sub StartFeedLoad( _ 
   ByVal bitsPerPixel As Integer, _ 
   ByVal order As CodecsLoadByteOrder, _ 
   ByVal firstPage As Integer, _ 
   ByVal lastPage As Integer _ 
)  

- (BOOL)startFeedLoad:(NSInteger)bitsPerPixel order:(LTCodecsLoadByteOrder)order firstPage:(NSInteger)firstPage lastPage:(NSInteger)lastPage error:(NSError **)error 

public FeedCallbackThunk startFeedLoad(int bitsPerPixel, CodecsLoadByteOrder order, int firstPage, int lastPage) 

public: 
void StartFeedLoad(  
   int bitsPerPixel, 
   CodecsLoadByteOrder order, 
   int firstPage, 
   int lastPage 
)  

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.

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.

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.
  6. You can also call the IsFeedLoadDone property to determine whether the framework has enough data to load the pages specified in firstPage and lastPage.

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.

Example

This example will use feed load to load a few pages of a multi-page file

C#
VB
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
using LeadtoolsExamples.Common; 
 
public void FeedLoadMultiExample() 
{ 
   RasterCodecs codecs = new RasterCodecs(); 
 
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Eye.gif"); 
   string destFileName = Path.Combine(LEAD_VARS.ImagesDir, "FeedLoadMulti.tif"); 
 
   // Load pages 2 through 5 from the file by reading chunks from the stream 
   codecs.StartFeedLoad(0, CodecsLoadByteOrder.BgrOrGray, 2, 5); 
 
   using (FileStream fs = File.OpenRead(srcFileName)) 
   { 
      const int bufferSize = 1024; 
      byte[] buffer = new byte[bufferSize]; 
 
      int read; 
 
      do 
      { 
         System.Windows.Forms.Application.DoEvents(); 
 
         read = fs.Read(buffer, 0, bufferSize); 
         Console.WriteLine("Feeding {0} bytes", read); 
         if (read > 0) 
            codecs.FeedLoad(buffer, 0, read); 
      } 
      while (read > 0 && !codecs.IsFeedLoadDone); 
   } 
 
   RasterImage image = codecs.StopFeedLoad(); 
   Console.WriteLine("{0} pages loaded", image.PageCount); 
 
   // Save the image to disk 
   codecs.Save(image, destFileName, RasterImageFormat.Tif, 1, 1, -1, 1, CodecsSavePageMode.Overwrite); 
   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 FeedLoadMultiExample() 
   Dim codecs As New RasterCodecs() 
 
   Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Eye.gif") 
   Dim destFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "FeedLoadMulti.tif") 
 
   ' Load pages 2 through 5 from the file by reading chunks from the stream 
   codecs.StartFeedLoad(0, CodecsLoadByteOrder.BgrOrGray, 2, 5) 
 
   Dim fs As FileStream = File.OpenRead(srcFileName) 
   Try 
      Const bufferSize As Integer = 1024 
      Dim buffer(bufferSize - 1) As Byte 
 
      Dim read As Integer 
 
      Do 
         System.Windows.Forms.Application.DoEvents() 
 
         read = fs.Read(buffer, 0, bufferSize) 
         Console.WriteLine("Feeding {0} bytes", read) 
         If (read > 0) Then 
            codecs.FeedLoad(buffer, 0, read) 
         End If 
      Loop While read > 0 AndAlso Not codecs.IsFeedLoadDone 
   Finally 
      fs.Close() 
   End Try 
 
   Dim image As RasterImage = codecs.StopFeedLoad() 
   Console.WriteLine("{0} pages loaded", image.PageCount) 
 
   ' Save the image to disk 
   codecs.Save(image, destFileName, RasterImageFormat.Tif, 1, 1, -1, 1, CodecsSavePageMode.Overwrite) 
   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

Help Version 20.0.2018.6.21
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Leadtools.Codecs Assembly