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EnableDoublePass Property

Gets or sets a value indicating whether to enable the double pass setting when reading PDF417 symbols.
public bool EnableDoublePass { get; set; } 
Public Property EnableDoublePass As Boolean 
@property (nonatomic, assign) BOOL enableDoublePass 
public boolean getEnableDoublePass() 
public void setEnableDoublePass(boolean value) 
property bool EnableDoublePass { 
   bool get(); 
   void set (    bool ); 

Property Value

true to use double pass when reading PDF417 symbols. Otherwise, false. Default value is false.


When reading 2D barcodes, LEADTOOLS can perform internal auto pre-processing on the image and try again if the engine cannot detect the required barcode. This may take extra processing and increase the barcode detection time. Therefore, it is best to set EnableDoublePass to true only in certain situations, as follows:

  • The application is reading barcodes of this type exclusively (for example, a dedicated PDF417 reader is being used). In this case, reading the barcodes is always more important than recognition speed.

  • The application uses barcode detection on a server. In this case, the time spent on the actual barcode detection is most probably less than the time required to send the image to the server and get the result back due to network latency. Thus it makes sense to enable double pass in this situation.

  • The images provided have a small resolution (DPI) or are known to come from a source that does not always provide clean images (for example, a Fax machine or a Scanner). Enabling double pass here ensures that the barcodes can be read regardless of the quality of the input image.

  • The LEADTOOLS .NET C# and VB Barcode demos leave double pass disabled by default. If the engine tries to read a PDF417 barcode but cannot find it, it will then ask the user if DoublePass should be enabled and reading be retried. An approach like that (or an automated one: Read. If failure, enable and read again) can also be used.


For an example, refer to PDF417BarcodeReadOptions.


Target Platforms

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