|
For the purpose of this document the smallest blob inside a Data Matrix symbol is defined as one print element. The physical size of a print element is user defined. It contributes to the overall size of a symbol when printing.
For proper recognition, the Data Matrix symbol section of a captured image must contain a sufficient number of pixels. Recognition rates are directly linked to the number of pixels contained in the X axis of each print element. Two pixel wide print elements yield a low recognition rate, provided that skew is kept to a minimum. Four or more pixel wide print elements yield a recognition rate of close to 100%, regardless of skew. Recognition may be unreliable or even impossible with images that do not match these requirements. Images with a high angle of skew require more pixels than images with little skew. Print quality and scanner settings also affect recognition rates.
Enlarging the printed symbol, increasing the scanner DPI, or moving the camera closer to the object increases the number of pixels in a print element. In a test image the actual number of pixel per print element can best be determined by downloading and installing the Axtel Demo. The demo is capable of reading .TIF and .BMP and .JPG files. Open the test image and position the cursor over one print element of the Data Matrix symbol. At the bottom right, the X position of the cursor is displayed at all times. The difference in X count between right and left edge of the print element must match or exceed the minimum requirement.
|