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StartOverlay Method

Indicates which method should be called when an overlay is detected inside a file.
- (BOOL)startOverlay:(nullable LTCodecsOverlayCallback)callback  
               error:(NSError **)error 
public void startOverlay(CodecsOverlayListener listener, CodecsOverlayCallbackMode mode) 
def StartOverlay(self,callback,mode): 


The method which should be called when an overlay is detected. Use a null reference to indicate that LEADTOOLS should handle overlays automatically.

Indicates when this method should be called. See CodecsOverlayCallbackMode for possible values.


Currently, only PTOCA files are known to use such overlays.

PTOCA files contain file references (i.e. filenames) to external files that contain overlay bitmaps. (These files are typically in IOCA format)

These external overlay files will be resized and placed on the current page according to the information from the PTOCA files. By default, LEADTOOLS will load these external overlay files from disk. You should override this behavior if you load files that are not stored locally (for example, on a remote storage or in a database).

To load overlays stored on other storage, you have to pass your overlay callback to this method and load the overlays in your overlay callback.

The overlay callback will be used until StopOverlay is called.


This example will read a PTOKA file and overlays a TIF file on it

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
void PtokaOverlayExample(string ptokaFileName, string ptokaFilesPath) 
   RasterCodecs codecs = new RasterCodecs(); 
   // Set up the private variables used in the callback 
   myCodecs = codecs; 
   myPtokaFilesPath = ptokaFilesPath; 
   // Set the overlay callback 
   codecs.StartOverlay(CodecsOverlayCallback, CodecsOverlayCallbackMode.CallLoad); 
   // Load the PTOKA file 
   RasterImage image = codecs.Load(ptokaFileName); 
   // Stop the overlay by resetting the old callback. 
   // Save the image as TIFF 
   string destFileName = Path.Combine(LEAD_VARS.ImagesDir, "PtokaOverlay.tif"); 
   codecs.Save(image, destFileName, RasterImageFormat.Tif, 1); 
   // Clean up 
RasterCodecs myCodecs; 
string myPtokaFilesPath; 
void CodecsOverlayCallback(CodecsOverlayData data) 
   // Show overlay information 
   Debug.WriteLine("File: {0}", data.FileName); 
   Debug.WriteLine("Page Number: {0}", data.PageNumber); 
   Debug.WriteLine("Info: {0}", data.Info); 
   // Construct the overlay file name 
   string overlayFileName = Path.Combine(myPtokaFilesPath, data.FileName); 
   if (data.Info) 
      // Info, we only need to fill in the .InfoXXX members of the data 
      CodecsImageInfo imageInfo = myCodecs.GetInformation(overlayFileName, false); 
      data.InfoWidth = imageInfo.Width; 
      data.InfoHeight = imageInfo.Height; 
      data.InfoXResolution = imageInfo.XResolution; 
      data.InfoYResolution = imageInfo.YResolution; 
      // We need to load the overlay image into the .Image member 
      data.Image = myCodecs.Load(overlayFileName); 
static class LEAD_VARS 
   public const string ImagesDir = @"C:\LEADTOOLS22\Resources\Images"; 

Target Platforms

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Leadtools.Codecs Assembly

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© 1991-2023 LEAD Technologies, Inc. All Rights Reserved.