Faxing Barcode Symbols
There are many cases where a developer will want to decode a barcode symbol which was faxed using either the Fax C++/ActiveX or some other means. Fax transmissions are highly susceptible to acquiring “noise” during the transmission which may block or break parts of the transmitted barcode. When faxing barcode symbols using the Fax C++/ActiveX, make sure that ECM (Error Correction Mode) is enabled, and try to send the faxes in Fine Fax resolution (204 x 196).
When faxing from a fax machine, often times this will result in white lines from the top of the image all the way to the bottom. If one of these white lines happens to split a single black bar from top to bottom, then that barcode symbol may no longer be recognized/decoded. In order to avoid this type of problem, the barcode symbol should be printed vertically onto the page.
Printing Barcode Symbols
Printing an image which contains a barcode and maintaining a high symbol recognition rate can be difficult, especially if the image must be scaled before printing. Scaling an image can produce distortion in the printed image and can result in low recognition rates.
For best results, the image that the Barcode symbol is created on should have settings which are as close as possible to the printer settings. For example, if printing to a printer which uses a resolution of 600 DPI, the initial image should be created with 600 DPI. Using the same DPI in your image and printer will allow the image containing the barcode symbol to be printed without having to perform any scaling to the image.
When printing from an application which will scale images to fit the printed page, if the image DPI and printer DPI cannot be matched for some reason, try to set the printer and Image DPI to fall within an integer ratio, such as 2:1. For example, with a 200 DPI image file, print to a printer using 600 DPI. This way, every pixel in the original image will be doubled, resulting in no additional distortion. Printing a 200 DPI image to a 300 DPI printer will result in every other pixel being doubled, which can add sever distortion to the barcode symbol, even though the barcode may appear correct to the human eye.
Reliably Decoding Barcode Symbols
In order to reliably read and decode barcode, the portion of the image containing the barcode symbol must contain a sufficient number of pixels. Barcode decoding rates are tied to the number of pixel contained in the horizontal direction for each element in the barcode. Barcode elements that are at least two pixels wide produce reliable decoding rates, as long as the angle of skew is kept relatively low. Elements with a pixel width of four or more produce can reliably be decoded no matter the skew angle. Images which do not meet these base requirements (containing single pixel wide elements or high levels of skew and low pixel widths) may be impossible to decode. Printer, scanner, and camera resolution also play a part in a barcode symbols decoding rate.
For best results when decoding barcode symbols, try to enlarge the printed symbol, increase the scanner, camera or printer DPI, or move the camera closer to the object. Performing as many of these steps as possible will increase the number of pixels in each barcode element. The more pixels per element, the higher the overall decoding success rate.
How can the Barcode recognition be improved?
The correctness and speed of barcode recognition depends on various factors, e.g. image quality, image resolution and compression.
In practice, the images containing barcode are noisy, distorted, or even injured. Although the prebuilt image processing steps and error-correction algorithms help to recognize these non-ideal images, not all level of errors can be compensated. The more noisy or distorted the image is, less the success in recognition it has.