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'[EE]: Fun with Statistics - Which is better?'
2003\04\17@125329 by Lawrence Lile

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Which unit is better?

I have two units, one is supposed to be "improved" over the other.  I ran
200 tests on each unit, and recorded the number of successful tests out of
each  group of ten tests.  I am trying to prove to myself whether one is
actually better than the other, or that the differences are insignifigant,
statistically.  Here is the raw data

Successful tests
out of ten tries

unit1   unit2
10      10
3       2
5       10
10      9
10      6
0       0
7       9
10      10
8       8
0       5
7       6
2       6
9       8
7       10
8       9
10      10
4       10
0       1
3       3

113     132 out of 200  total # tests
57%     66% success rate

Avg     5.947368421     6.947368421     Average
St. Dev 3.703957106     3.341218743     St Dev

Now on the surface Unit 2 looks slightly better than unit 1.  However, the
standard deviations are so large, maybe it is just a statistical fluke and
next time unit 1 will look better.  Any body got enough math whizzing
around their brain to tell?

P.S. THe manufacturer says the tests should be 95% successful.  Yeah
right.

--Lawrence the Skeptical


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2003\04\17@132311 by Tom Messenger

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Statistics are great fun, no?

Your information presented so far is a bit vague for someone to guess which
is better... the data looks questionable from the scatter to start with.

Of course, other details might be important to know: if the "units" are rf
comm gear transmitting data over ten miles of range subject to various
noise sources, and the end user environment can deal with drop outs by
simply retrying (send again) then both of these might well surpass the
necessary quality level required by the enduser. Or maybe the "units" are
parachutes?  Guillotines?

Tom M.

At 11:47 AM 4/17/03 -0500, you wrote:
>Which unit is better?

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2003\04\17@144147 by Lawrence Lile

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The "units" are a pair of midget captains operating a winch that drives an
archimedes screw emptying a bathtub causing the bather to stand up and
shout "Eureka!" whereupon he bonks his head and as he passes out reads a
UPC code off of a product label.  NO WAITAMINUTE WRONG PROJECT  ;-)

THey are barcode scanners.  And yes, the user can try again if they don't
work the first time, unless he gives up and flings them across the room at
the bather.  At 60% accuracy I give that a 50-50 chance of happening.
(how's that for statistics huh?)



-- Lawrence Lile





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Statistics are great fun, no?

Your information presented so far is a bit vague for someone to guess
which
is better... the data looks questionable from the scatter to start with.

Of course, other details might be important to know: if the "units" are rf
comm gear transmitting data over ten miles of range subject to various
noise sources, and the end user environment can deal with drop outs by
simply retrying (send again) then both of these might well surpass the
necessary quality level required by the enduser. Or maybe the "units" are
parachutes?  Guillotines?

Tom M.

At 11:47 AM 4/17/03 -0500, you wrote:
>Which unit is better?

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2003\04\17@145424 by Herbert Graf

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> The "units" are a pair of midget captains operating a winch that drives an
> archimedes screw emptying a bathtub causing the bather to stand up and
> shout "Eureka!" whereupon he bonks his head and as he passes out reads a
> UPC code off of a product label.  NO WAITAMINUTE WRONG PROJECT  ;-)
>
> THey are barcode scanners.  And yes, the user can try again if they don't
> work the first time, unless he gives up and flings them across the room at
> the bather.  At 60% accuracy I give that a 50-50 chance of happening.
> (how's that for statistics huh?)

       From what I've seen of typical scanners your "results" are probably bang
on. I often see cashiers just give up scanning certain items and entering
the numbers in manually. Blame the product manufacturers, some products are
in packaging that just prevents good scans. TTYL

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2003\04\17@152312 by Dave VanHorn

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>
>THey are barcode scanners.  And yes, the user can try again if they don't
>work the first time, unless he gives up and flings them across the room at
>the bather.  At 60% accuracy I give that a 50-50 chance of happening.
>(how's that for statistics huh?)

How confident are you that the test targets are valid?
PSC makes validators, but they are a bit pricey.

Are these hand scanned or laser/video/ccd?
Clean optics on both units?

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2003\04\17@152316 by erholm (QAC)

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Hi.

You *are* using a correct combination of scanner,
labels, label printer, printer ribbon (if thermo-transfer) ?

Have you verified that the labels you are reading are
confirming to the standards ? There are special optical
instruments for that. If not, how can you know that it
isn't your labels that are "bad".

What label coding are you using ?
(I'v worked a lot with labels with Code-128C that
was "on the edge" of the standars, and we had quite
a lot of problems to select working scanners. Any
scanner that wasn't "high-dens" just didn't work at all.)
In general, old plain Code-39 seems to be the easiest
to read.

It's hard to say anything about your results without
all details about the used barcode, label material,
the printer type/mark/model, scanner specs.

Tha fact that your results vary a lot, tells me that
at least one of the components are on the edge. *Could* be
the scanner, but you can't realy be sure.

Has the scanner producer had a look at your labels ? And
in that case, what did he say about them ?

Jan-Erik Soderholm.

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2003\04\17@153353 by Olin Lathrop

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> THey are barcode scanners.  And yes, the user can try again if they
> don't work the first time, unless he gives up and flings them across
> the room at the bather.  At 60% accuracy I give that a 50-50 chance of
> happening. (how's that for statistics huh?)

60% for a barcode scanner sucks.  That means that one in every 16 attempts
to read a new barcode will be unsuccessful after three attempts.  After
three failed scans in a row, a user may very well conclude the scanner is
broken an ditch it, or get very frustrated, and annoyed at the !$&#*@!*^
that picked that brand scanner.


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Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2003\04\17@153610 by Olin Lathrop

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>         From what I've seen of typical scanners your "results" are
> probably bang on. I often see cashiers just give up scanning certain
> items and entering
> the numbers in manually. Blame the product manufacturers, some products
> are
> in packaging that just prevents good scans. TTYL

Yes, I've seen a cashier occsionally unable to scan a particular package.
However, that is quite rare.  The vast majority of scans work just fine.
You don't see anywhere near 4 out of 10 failing.


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(978) 742-9014, http://www.embedinc.com

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2003\04\17@154223 by Lawrence Lile

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They are hand operated scanners, introducing the variability of hand speed
and position.  They are definitely *not* pricey, so it is not surprising
that they are not great acuracy.  No laser here, they use an LED and a
lens.



-- Lawrence Lile
Senior Project Engineer
Toastmaster, Inc.
Division of Salton, Inc.
573-446-5661 voice
573-446-5676 fax




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>
>THey are barcode scanners.  And yes, the user can try again if they don't
>work the first time, unless he gives up and flings them across the room
at
>the bather.  At 60% accuracy I give that a 50-50 chance of happening.
>(how's that for statistics huh?)

How confident are you that the test targets are valid?
PSC makes validators, but they are a bit pricey.

Are these hand scanned or laser/video/ccd?
Clean optics on both units?

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2003\04\17@154228 by Lawrence Lile

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These are just products pulled from the selves. I'm not familiar with all
the barcode standards, nor did I develop these scanners, just charged with
testing them.  So these are not lab-accurate barcode labels, but they are
indicitive of what the customer would experience.

-- Lawrence Lile
Senior Project Engineer
Toastmaster, Inc.
Division of Salton, Inc.
573-446-5661 voice
573-446-5676 fax




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Hi.

You *are* using a correct combination of scanner,
labels, label printer, printer ribbon (if thermo-transfer) ?

Have you verified that the labels you are reading are
confirming to the standards ? There are special optical
instruments for that. If not, how can you know that it
isn't your labels that are "bad".

What label coding are you using ?
(I'v worked a lot with labels with Code-128C that
was "on the edge" of the standars, and we had quite
a lot of problems to select working scanners. Any
scanner that wasn't "high-dens" just didn't work at all.)
In general, old plain Code-39 seems to be the easiest
to read.

It's hard to say anything about your results without
all details about the used barcode, label material,
the printer type/mark/model, scanner specs.

Tha fact that your results vary a lot, tells me that
at least one of the components are on the edge. *Could* be
the scanner, but you can't realy be sure.

Has the scanner producer had a look at your labels ? And
in that case, what did he say about them ?

Jan-Erik Soderholm.

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2003\04\17@154641 by Lawrence Lile

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>very frustrated, and annoyed at the !$&#*@!*^ that picked that brand scanner

Yup.  I hope to have a better scanner yet in a few weeks, and have a good
method of comparing the new and old.


-- Lawrence Lile





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> THey are barcode scanners.  And yes, the user can try again if they
> don't work the first time, unless he gives up and flings them across
> the room at the bather.  At 60% accuracy I give that a 50-50 chance of
> happening. (how's that for statistics huh?)

60% for a barcode scanner sucks.  That means that one in every 16 attempts
to read a new barcode will be unsuccessful after three attempts.  After
three failed scans in a row, a user may very well conclude the scanner is
broken an ditch it, or get very frustrated, and annoyed at the !$&#*@!*^
that picked that brand scanner.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2003\04\17@155125 by Dave VanHorn

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At 02:35 PM 4/17/2003 -0500, Lawrence Lile wrote:
>They are hand operated scanners, introducing the variability of hand speed
>and position.  They are definitely *not* pricey, so it is not surprising
>that they are not great acuracy.  No laser here, they use an LED and a
>lens.

First read rate on any properly printed symbols should be >>90%
Substitution errors on UPC or code 39 should be near zero, but I-2 of 5 is
pretty bad that way.

I can test your targets for you if they're mailable, and you can wait till
I get home.

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2003\04\17@161950 by

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Then I don't think they are *scanners* at all.
Scanners you don't move, *they* do the "scanning" for you.
A scanner has either a *row* of leds or a laser
and a rotating mirror.

They look as a thick pen, right?

Anyway, I'v seen barcode pens (HP in that case) come in at least
three different models, low, medium and high resolution.
Not meening "good", "better" and "best", just that you
have to select the reader according to the resolution of
the labels you are going to read.

And these readers are quite sensitive to how you hold them.
The angle between the reader and the label is important.

Jan-Erik.

Lawrence Lile wrote:
>They are hand operated scanners, introducing the variability of hand speed
>and position.  They are definitely *not* pricey, so it is not surprising
>that they are not great acuracy.  No laser here, they use an LED and a
>lens.

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2003\04\17@163546 by Dave VanHorn

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>
>Anyway, I'v seen barcode pens (HP in that case) come in at least
>three different models, low, medium and high resolution.
>Not meening "good", "better" and "best", just that you
>have to select the reader according to the resolution of
>the labels you are going to read.

Too small, and you see lots of noise.
Too large, and the bars and spaces get "fuzzy"

>And these readers are quite sensitive to how you hold them.
>The angle between the reader and the label is important.

True.

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2003\04\17@170155 by Wagner Lipnharski

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Lawrence Lile wrote:
> These are just products pulled from the selves. I'm not familiar with
> all the barcode standards, nor did I develop these scanners, just
> charged with testing them.  So these are not lab-accurate barcode
> labels, but they are indicitive of what the customer would experience.


That's the thing.

You can't test accuracy of a scanner based on trashed printed barcodes.

You can, of course, in a cheap way use a 100% readable barcode, then play
with ambient light and distance between the scanner and the object, and
only then, make some comparison between two scanners, when one fails, other
doesn't.

There are plenty of dumb stupid label designer around, they don't even
realize that making a barcode in yellow over a bare aluminum can will
result in bad reading.  Most of scanners use red light (led or laser), very
few label designers understand what red light means, it means that blue
over black still dark for the scanner.  If you can't ensure a white
contrasting with dark color, then use red with any other contrasting color.
The best approach is using an easy made red acrylic eyeglasses to find out
the best contrast.

You can not misjudge a scanner just because the label designer is dumb.

USPS counter scanners are expensive and don't work.  Whenever I send
Priority Mail, they need to scan and scan, several times, until the darn
scanner respond.  In my company we use only Cipher laser scanners, 100%
accurate in all kind of barcodes, even at 8" away.  USPS large labels can
be read from more than 15".

Wagner.

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2003\04\17@171900 by Dave VanHorn

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>
>You can't test accuracy of a scanner based on trashed printed barcodes.

I've been known to test the decode algorithms that way..
Printing the targets with progressively higher distortion.

There are a number of things to look at here, starting with the reading
pens, scan method, and target accuracy.

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2003\04\17@175434 by Wagner Lipnharski

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Dave VanHorn wrote:
>> You can't test accuracy of a scanner based on trashed printed
>> barcodes.
>
> I've been known to test the decode algorithms that way..
> Printing the targets with progressively higher distortion.
>
> There are a number of things to look at here, starting with the
> reading pens, scan method, and target accuracy.


Almost 100% of the scanners (not pens) use to select one pure video line
from the CCD.
Some scanners use to buffer several lines (according to memory available),
spaced by 10 lines or so, to be used in case the barcode could not be
decoded from the video line under analysis.

So, everything is based on the CCD quality and resolution, lumens
sensitivity, electronic shuttle speed and such.

Wagner.

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2003\04\17@183728 by Bob Ammerman

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I would think a comparison between two readers using the same target
barcodes would be meaningful, no matter what shape the barcodes were in.

In fact, if I were tasked with this project I would expend significant
effort to get a good sampling of different typical barcodes to use with the
two readers.

With a large enough sample size you could certainly determine which reader
would be better in the real word.

btw: One of these readers isn't the infamous CueCat(tm) is it  :-)

Bob Ammerman
RAm Systems


{Original Message removed}

2003\04\17@185809 by Lawrence Lile

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Nope, not a cuecat.  I'd say this is more like a cuemouse, or maybe even a
cueparamecium ;-)  a cat would have a lot more processing power than this.



-- Lawrence Lile





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I would think a comparison between two readers using the same target
barcodes would be meaningful, no matter what shape the barcodes were in.

In fact, if I were tasked with this project I would expend significant
effort to get a good sampling of different typical barcodes to use with
the
two readers.

With a large enough sample size you could certainly determine which reader
would be better in the real word.

btw: One of these readers isn't the infamous CueCat(tm) is it  :-)

Bob Ammerman
RAm Systems


{Original Message removed}

2003\04\17@190023 by Lawrence Lile

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I guess this falls more in the pen catagory.

-- Lawrence Lile
Senior Project Engineer
Toastmaster, Inc.
Division of Salton, Inc.
573-446-5661 voice
573-446-5676 fax




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Dave VanHorn wrote:
>> You can't test accuracy of a scanner based on trashed printed
>> barcodes.
>
> I've been known to test the decode algorithms that way..
> Printing the targets with progressively higher distortion.
>
> There are a number of things to look at here, starting with the
> reading pens, scan method, and target accuracy.


Almost 100% of the scanners (not pens) use to select one pure video line
from the CCD.
Some scanners use to buffer several lines (according to memory available),
spaced by 10 lines or so, to be used in case the barcode could not be
decoded from the video line under analysis.

So, everything is based on the CCD quality and resolution, lumens
sensitivity, electronic shuttle speed and such.

Wagner.

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2003\04\17@193503 by Dave VanHorn

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At 06:35 PM 4/17/2003 -0400, Bob Ammerman wrote:
>I would think a comparison between two readers using the same target
>barcodes would be meaningful, no matter what shape the barcodes were in.

IF you can assure the scan happens over the same points in the target.
Otherwise the input to the algorithm can be significantly different.

If you're testing decode algorithms, you can code up a micro to send
perfect, and variously damaged waveforms, so that it's always repeatable,
but it's a giant PITA.
Good for regression testing though.

What I've done in the past, is to output the scan widths in hex form, prior
to the decode, then add the decoded data appended as a comment.
Capture the whole thing in hyperterminal, then weed out the good scans.
Take the bad scans, include them in the next code assemble, then hand-fly
the decoder through it's logic to see if the scan should have read ok, or
where the logic failure is.  It's somewhat less of a PITA that way. Of
course you need a micro with a uart, and/or enough spare code space to do
that.

>In fact, if I were tasked with this project I would expend significant
>effort to get a good sampling of different typical barcodes to use with the
>two readers.

I have a little book of nasty barcodes from real products.  Given the HUGE
penalties that large retailers put on bad barcodes, it's amazing how many
are out there in the real world.

>With a large enough sample size you could certainly determine which reader
>would be better in the real word.

As long as you're careful about what sorts of errors you allow.
Some are out of spec, and could bias the results unfairly.

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2003\04\17@210635 by M. Adam Davis

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You probably mean 100% of the CCD scanners.

The barcode scanners I purchase for use at video stores are laser, and
have a wobbling mirror with one diode laser and one photodiode
detector.  They do, however, keep decoding until something valid scans,
and the laser goes back and forth dozens of times a second.

The only time I have a hard time scanning is when I'm trying to scan a
very badly printed label, or when they are broken.

But then we also use thermal transfer wax/resin on polyester labels
which don't scratch, get wet, stretch, mar, darken over time, etc.

-Adam

Wagner Lipnharski wrote:

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2003\04\17@212636 by M. Adam Davis

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I haven't taken statistics, but my spider sense tells me that you've got
a 'six of one, half a dozen of the other' situation here.

Pen barcode wands are not good for materials that can stretch and warp
or are oddly shaped, simply because a person generally cannot keep the
material flat /and/ scan at an even rate and constant angle at the same
time.  They work great for hard, flat items such as books, boxes, etc.
They'll be absolutely terrible for bagged bread, cans and bottles, etc.

But it sounds like you don't have the job of determining what type of
scanner to use for this application.  You get to choose between two evils.

Were I you, I'd find out what conditions the workers were under, how
often they had to scan, what's the height they generally scan at, how do
they typically hold the package and the pen, etc.  Then I'd not only
take the types of products they are scanning and work at that level, I'd
also try to find marginal barcodes, and ideal barcodes and use them in
that environment.

The main issue here is not whether they'll have a lot of bad scans (we
know that they will) it's whether they will have enough of them that
they'll simply lay the pen down and type them all in since it'll take
less time to type a barcode than it is to pick it up, try scanning it,
and putting it down and typing it in when it fails.

You might want to make the point that if they use even a low end laser
scanner they may realize a greater return on investment because they
will simply not be dropped and picked up so frequently, since an entire
order can be scanned in without having to use the keyboard.  If you have
to replace the pen more than once a year you aren't just paying for the
pen, but also the shipping, storage, installation, and downtime.  At
that rate, a $20 pen that lasts 3-4 months is more expensive than a $200
handheld laser scanner, and your employees will be happier to boot.

But in 5 years it won't matter - RFID is coming.  I can't wait for
barcodes to dissappear, and to be able to walk out with my purchase
being tallied and account charged as I walk past the scanners...

-Adam

Lawrence Lile wrote:

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2003\04\18@004615 by William Chops Westfield

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Oh yeah.  The original question.  Your description of actual test was
important.  I don't think you can just add up the total number of failures,
since it looks like the "improvements" in unit 2 were for particular cases
of barcode "legibility."  So I think you should look at the amount of
improvement or decline for each case...

It looks to me like there are 5 cases where unit 2 does significantly better
(more that 2 more recognitions) than unit number 1:

>5       10
>0       5
>2       6
>7       10
>4       10

There is only ONE case where unit 1 appears to do significantly better:
>10      6

There are a number of cases where one is slightly better than the other,
which I discarded as liable to go either way on re-testing.

BillW

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2003\04\18@133611 by Peter L. Peres

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>barcode readers

Maybe you pushed the bad print on the barcode a little too far ? (about as
far as it goes in real life - oh wait - you DIDN'T test with genuine food
greasy, wet, frozen packages from the supermarket, did you ?)

Peter

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2003\04\18@135313 by Dave VanHorn

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At 08:59 PM 4/18/2003 +0300, Peter L. Peres wrote:
> >barcode readers
>
>Maybe you pushed the bad print on the barcode a little too far ? (about as
>far as it goes in real life - oh wait - you DIDN'T test with genuine food
>greasy, wet, frozen packages from the supermarket, did you ?)

On upc/ean, the workable distortion spec is pretty limited.
I've been able to recover some pretty badly distorted codes, up to but not
including 0.5 module, because once you hit half a module, you can't
determine wether it was made larger or smaller..

Other symbologies aren't nearly so robust.

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2003\04\23@062150 by Alan B. Pearce

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>>> You can't test accuracy of a scanner based on trashed printed
>>> barcodes.
>>
>> I've been known to test the decode algorithms that way..
>> Printing the targets with progressively higher distortion.
>>
>> There are a number of things to look at here, starting with the
>> reading pens, scan method, and target accuracy.
>
>
>Almost 100% of the scanners (not pens) use to select one pure video line
>from the CCD.
>Some scanners use to buffer several lines (according to memory available),
>spaced by 10 lines or so, to be used in case the barcode could not be
>decoded from the video line under analysis.
>
>So, everything is based on the CCD quality and resolution, lumens
>sensitivity, electronic shuttle speed and such.

One of the best discourses I have seen on doing this with a wand type reader
is in the Motorola 6800 books that came out early on. There is a big thick
book, I think called an "Application Handbook" that had a discussion on
doing a POS terminal, as a way of introducing printing, keyboard scanning,
display drive and included UPC code scanner with code to deal with
determining the scan speed of the wand.

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2003\04\23@062607 by Alan B. Pearce

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>I would think a comparison between two readers using the same target
>barcodes would be meaningful, no matter what shape the barcodes were in.
>
>In fact, if I were tasked with this project I would expend significant
>effort to get a good sampling of different typical barcodes to use with the
>two readers.

But I would make sure that the barcodes being tested fell within
specifications for line widths/ratios contrast ratios etc that might be
relevant. Once you get to a point where these can be read with low failure
rates, then you can start comparing out of spec rates.

>btw: One of these readers isn't the infamous CueCat(tm) is it  :-)

Certainly sounds like it from my experience with one :))

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