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Invisible schrieb:
>> http://www.herdsoft.com/ti/davinci4/examples/barcodecgi.cgi is
>> convinced that it is a "Code 39" (aka "Code 3 of 9") barcode, and
>> indeed correctly reads it as "UKM11001L3".
>
> Really? (I can't even tell what language that page is in.)
That's German of course :-)
>> BTW, Wolfram is doing a poor job at generating Code 39 barcodes, as it
>> uses different bar widths for the "frame" than for the "payload".
>>
>> (The Code 39 frame is usually interpreted as a leading and trailing
>> asterisk (*) character, as it uses the same bar sequence.)
>
> I especially love the way the bar widths don't appear to be multiples of
> each other. I almost wonder if the image has been scaled down by
> rounding each bar to a whole number of pixels, so some "thin" bars are 3
> pixels and some are 4... It's very districting!
It is less surprising once you know that Code39 doesn't have fixed bar
width ratios - just "narrow" and "wide" black and white bars (with each
character having 3 "wide" and 6 "narrow" bars, and characters separated
by another white bar; don't know if that is mandatorily narrow, though
it seems common).
> Indeed, clicking on "PDF" and enlarging the image seems to make the
> problem go away... How annoying!
Why not get one of those many Code39 TrueType fonts out there?
... or write a POV-Ray SDL script to generate barcode images :-)
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>> I especially love the way the bar widths don't appear to be multiples
>> of each other. I almost wonder if the image has been scaled down by
>> rounding each bar to a whole number of pixels, so some "thin" bars are
>> 3 pixels and some are 4... It's very districting!
>
> It is less surprising once you know that Code39 doesn't have fixed bar
> width ratios - just "narrow" and "wide" black and white bars.
It's still confusing to have several apparently different bar widths
which are actually supposed to be "the same". The reader might accept
it, but for a visual example, it's sucky.
> Why not get one of those many Code39 TrueType fonts out there?
>
> ... or write a POV-Ray SDL script to generate barcode images :-)
Why use SDL when you can use PostScript, the language of the laser
printers? ;-)
I have in fact just written a working code-128 reader/writer today. It
only deals with bit-sequences, but I guess the next step is to handle
actual pictures...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Invisible wrote:
> Hahaha, well... it turns out there are actually a miriad of different
> kinds. And they're ALL COMPLETELY DIFFERENT to each other.
Interestingly, though, they all seem to have quite characteristic
start/end markers. It appears to be possible to uniquely discriminate
them by this alone.
(For example, UPC-A and EAN-13 both start and end with ...01010...)
> I just did a cursory scan of my office.
I see what I did there. ;-)
> Here's what I found:
>
> SIIG USB-serial box: UPC-A barcode plus one of unknown type.
This appears to be Code-39. (Begins 10010... and ends ...0101101101.)
I'm guessing it encodes the serial number also printed above the barcode.
> Maxtor drive: 5 barcodes of unknown type.
These all appear to be Code-128. (Begins 11010... and ends ...11101011.)
> Integral RAM box: One barcode (from Insight UK) of unknown type.
This seems to be Code-39 again. (I'm guessing it encodes the large part
number printed above, not the smaller description text.)
> TNT shipping box: Two barcodes of unknown type.
I no longer have the box.
> HP laptop adaptor: 3 barcodes of unknown type.
Two of these appear to be Code-39. The final one might be Code-93. Maybe.
> It's great fun. EAN-13 is apparently an "extension" of UPC-A, and yet
> it's COMPLETELY DIFFERENT. The encoding is entirely unrelated.
From what I can tell, the two utterly different algorithms are supposed
to produce the same output in the case of an EAN-13 where the extra
digit happens to be zero. I haven't varified how this is possible yet.
> The impressive thing is, as far as I can tell, almost all barcode
> scanners support almost all kinds of barcodes. Even though each coding
> scheme is utterly unrelated to any of the others. God only knows how
> this is physically possible...
Again, it appears the start and stop markers are actually pretty unique
to each barcode type. It seems to be possible to distinguish them by
that alone, without the aid of a computer...
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