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Reading Barcodes from an Image - II

, 21 Aug 2010 CPOL
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An example of how to process an image for barcode strings
Sample Image

Introduction

I recently ran across Benjamin Liedblad's article on reading barcode strings from images. The code was good, but not very useful in the real world. I thought my additions had a place here.

Berend Engelbrecht has vastly improved this project. His new version can be found at BarcodeImaging3.aspx.

Background

Liedblad's barcode reader has two significant flaws:

  • It only reads right-side up barcodes (as he mentioned in his "todo").
  • It assumes that there is nothing other than the barcode in the image.

Frequently, we need to read a barcode from a page full of other text. This is what I set about to do.

Using the Code

First of all, you should check out the original article to see how the barcode reading works. Much of the code is left unchanged.

Changes:

  • Since the barcode we are looking for may not be at the beginning of the text line that we scan, we can't just scan by blocks of 9 'characters'. Instead, we walk along the scanned pattern one 'bar' at a time, testing it and the 8 bars after it to see if they form a character. If we find a real character, then we skip over the character pattern and begin again.
  • Since there are text and other distractions on many pages, we need to cut the page up into sections and look for barcodes in each section. I've found that 50 is a good number of sections. While this seems like a lot, it's enough to ensure that we get the barcode we're looking for. Your mileage may vary. To this end, I added a startheight and endheight to ReadCode39(). Then we just need to calculate where each section begins and ends. This is accomplished easily in a for loop:
    for (int i=0; i < numscans; i++)
    {
        read = ReadCode39(bmp,i * (bmp.Height / numscans), 
               (i * (bmp.Height / numscans))+ (bmp.Height / numscans));
        [...]
    }
  • We need to check all four page orientations, which is handled easily with .NET's Bitmap control:
    for (int i=0; i < 4; i++)
    {
        bmp.RotateFlip(System.Drawing.RotateFlipType.Rotate90FlipNone);
        VScanPageCode39(ref CodesRead, bmp,numscans);
    }

    You can, of course not use this if you know that all of your pages are the right way up.

  • Finally, since we scan so many times and receive so many barcodes (including the backwards version of what we are looking for), we need to store all of the barcodes that we found. For this, I decided to use an ArrayList. The code currently returns all of the barcodes, but since most people supply some sort of pattern to their code (usually beginning and ending with astericks "*"), it's easy enough to pick out the right one.

Running the Demo

When you run the demo and load "SamplePage.jpg", first perform "Scan Barcode". This is essentially identical to Liedblad's original code. You will get "*JR7". Not very helpful. Then perform "Scan Page". Now you have a list of barcodes, one of which is the one you want (*surprise*)... and one is its mirror image (P4 9V*VK P). As you can see, it's pretty easy to pick out what you need.

History

  • 5-15-05: Original
  • 8-20-10: Article updated

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

qlipoth
Software Developer (Senior) InGage Networks
United States United States
James is currently a Software developer after a detour from that profession into IT because he 'didn't want to sit in a cubicle and wanted to deal with people.' He has since learned that people are stupid, and enjoys his cubicle greatly.

Comments and Discussions

 
GeneralRe: Great topic PinmemberOllipolli20-Jan-06 2:31 
GeneralRe: Great topic Pinmembervbdotnetcoder200520-Jan-06 11:51 
GeneralRe: Great topic Pinmemberqlipoth5-Feb-06 16:03 
GeneralRe: Great topic Pinmemberqlipoth5-Feb-06 16:08 
GeneralRe: Great topic PinmemberRudy P11-Feb-06 0:59 
GeneralRe: Great topic Pinmemberqlipoth14-Feb-06 4:26 
GeneralRe: Great topic PinmemberStephanGreiwe20-Oct-06 23:45 
GeneralRe: Great topic PinmemberSection8NZ22-May-07 20:20 
I'm doing some work in the area of reading barcodes off a webcam. It will tolerate barcodes at any angle.
 
heres a screenshot of the inital work showing detection of barcode portion of an image.
 
http://i44.photobucket.com/albums/f29/Section8NZ/barcodes.png[^]
 
I'll be releasing this as open source when its ready.
GeneralRe: Great topic PinmemberBruceN8-Jul-07 17:18 
GeneralRe: Great topic PinmemberSection8NZ8-Jul-07 22:12 
GeneralRe: Great topic PinmemberKerem Kat8-Apr-08 13:14 

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