National Instruments IMAQTM 用户手册

© National Instruments Corporation

By default, 

CWIMAQVision.ReadDataMatrixBarcode

 automatically 

detects the type of barcode to read. You can improve the performance of the 
function by specifying the type of barcode in the application. IMAQ Vision 
supports Data Matrix types ECC 000 to ECC 140, and ECC 200.

Use 

CWIMAQVision.ReadPDF417Barcode

 to read values encoded in a 

PDF417 barcode.

By default, 

CWIMAQVision.ReadPDF417Barcode

 automatically locates 

one or multiple PDF417 barcodes in an image. However, you can improve 
the inspection performance by locating the barcodes using one of the 
techniques described in the 

 section, 

and then passing in Regions of the locations into 

CWIMAQVision.ReadPDF417Barcode

.

If you need to read only one barcode per image, set the SearchMode parameter to 

cwimaqBarcode2DSearchSingleConservative

 to increase the speed of the method.

You can display the results obtained at various stages of the inspection 
process on the window that displays the inspection image by overlaying 
information about an image. The software attaches the information that you 
want to overlay to the image, but it does not modify the image. 
Access overlays using the 

CWIMAQImage.Overlays

 property. The 

CWIMAQOverlays collection contains a single CWIMAQOverlay 
object that you can access using 

CWIMAQImage.Overlay(1)

.

The 

CWIMAQImage.Overlays

 collection does not support usual collection 

methods—such as 

Add

, 

Remove

, and 

RemoveAll

—because they are reserved for 

future use.

Use the following methods on the CWIMAQOverlay object to overlay 
search regions, inspection results, and other information, such as text and 
pictures. Overlays on a viewer image are automatically updated when you 
call one of these methods.

•

DrawLine

—Overlays a CWIMAQLine object on an image.

•

DrawConnectedPoints

—Overlays a CWIMAQPoints collection 

and draws a line between sequential points.