Subj : writing a software barcode reader
To   : comp.programming
From : Eric.Medlin
Date : Wed Oct 05 2005 01:32 pm

I am writing software that will read a bar code from a 1bit tiff.  It
will need to return the barcode numbers, magnification, and bar width
reduction.  However I am having a hard time trying to determine the
magnification and the bar width reduction.  The sample bar code I am
reading starts with 30 1's then 60 0's then 29 1's.  This is the left
hand guard bars.  I have no clue why the 1's are not the same length.
Has anyone else noticed similar things when examing barcodes bit by
bit?  Remeber this is being read from the actual 1 bit tiff file that
will be printed this is not data from a hand held scanner.  I never
expected to find any noise, but it looks like I might.  Or maybe it is
just round off errors from the software that created the barcode.  Any
way from this I thought I could compute the magnification and bar width
reduction.  The file is 2400dpi so with no bar width reduction or
magnification a module should be 31 dots.  So the first two modules
should be 62.  The first two in the actually bar code are 90.  If we
take 90/62 we get 1.4516.  I know the barcode was created with a 145%
magnification, so this seems correct.  Now to find the bar code width
reduction.  With 145% magnification the first module should be 45 dots.
 So, (45-30)/2400 equals 0.00625.  I know the bar code was created with
a bar width reduction of 0.007.  That is close, but not perfect.  Has
anyone else done this and if so how?

.