National Instruments IMAQTM - Manual (Page 82)

Chapter 5 Performing Machine Vision Tasks
IMAQ Vision for Visual Basic User Manual 5-30 ni.com
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Interleaved 2 of 5, MSI, and UPCA.
Read Data Matrix Barcode
Use CWIMAQVision.ReadDataMatrixBarcode to read values encoded
in a Data Matrix barcode. This method can automatically determine the
location of the barcode and appropriate search options for the application.
However, you can improve the performance of the application by
specifying control values specific to the application.
CWIMAQVision.ReadDataMatrixBarcode can automatically locate
one or multiple Data Matrix barcodes in an image. However, you can
improve the inspection performance by locating the barcodes using one of
the techniques described in the
Instrument Reader Measurements section,
and then passing the Regions parameter into
CWIMAQVision.ReadDataMatrixBarcode .
Tip If you need to read only one barcode per image, set
CWIMAQDataMatrixOptions.SearchMode to
cwimaqBarcode2DSearchSingleConservative to increase the speed of the method.
By default, CWIMAQVision.ReadDataMatrixBarcode determines if the
barcode has black cells on a white background or white cells on a black
background.
Note Specify round cells only if the Data Matrix cells are round and have clearly defined
edges. If the cells in the matrix touch one another, you must set CellShape to
cwimaqBarcode2DCellShapeSquare .
By default, CWIMAQVision.ReadDataMatrixBarcode assumes the
barcode cells are square. If the barcodes you need to read have round cells,
set the
CellShape member of the CWIMAQDataMatrixOptions object to
cwimaqBarcode2DCellShapeRound .
Set the BarcodeShape member of the CWIMAQDataMatrixOptions
object to cwimaqBarcode2DShapeRectangular or
cwimaqBarcode2DShapeSquare depending on the shape of the
barcode you need to read.
Note Setting the BarcodeShape member of the CWIMAQDataMatrixOptions object to
cwimaqBarcode2DShapeRectangular when the barcode you need to read is square
reduces the reliability of the application.