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RE: Barcode performance



 Thank-you Don,
 It is always a pleasure to hear it from the true authority.And I hope
the folks at the labs are looking in.
                   Respectfully,
                                Randy Coonfield

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From: 	verploeg at eznet.net
Sent: 	Saturday, November 16, 1996 10:58 AM
To: 	telecine at xyzoom.alegria.com
Subject: 	RE: Barcode performance

I've followed with great interest over the past week, the dialog on barcode 
performance.  Unfortunately, I've not had a chance to respond until now.  
This being one of my main consulting areas for Kodak Professional Motion 
Imaging, I'd like to add a few facts, figures and observations.  I 
apologize for the lengthy reply, but hopefully, it will provide some useful 
insight.

As many of you point out, generally there's little difficulty reading 
Keykode numbers on negative films using modern barcode readers.  You should 
be able to set the sensitivity of a modern Keykode reader and expect to get 
accurate barcode readings without further adjustment for any camera stock 
in the same format.  Of course, reader sensitivity may need to be adjusted 
going from 35mm to 16mm films and from negative to reversal stocks.

Early Keykode Numbers and Readers:
As some of you have also pointed out, the edgeprint density on older 
Eastman 35mm B&W negative, particularly 5222 manufactured shortly after 
Kodak introduced Keykode numbers late 1989, required a higher reader light 
intensity.  In fact, the edgeprinting on all Kodak films first coded with 
Keykode numbers was denser than today.  Back then, readers were not readily 
available to determine if a different edgeprint exposure would be needed.  
It was decided best to maintain previous standards based on optimum human 
readability.

As Keykode readers became more prevalent and users provided feedback, we 
learned that the barcode exposure on those early stocks was greater than it 
needed to be.  Also, some of the first Keykode readers lacked the higher 
intensity required to read the denser code.

Five years ago, Kodak reduced the edgeprint exposure on all Eastman color 
stocks to improve machine readability, but not so much as to impair human 
readability.  The min - max density tolerances were narrowed for greater 
consistency across all product lines.  The same parameters were applied to 
Eastman B&W films in early 1993.

However, B&W camera films are "push-processed" much more frequently than 
color films, and a few transfer facilities continued to report problems 
reading the barcode.  So, in the spring of '95, responding to user 
requests,  Kodak reduced the latent edgeprint exposure on its B&W films a 
bit further.

Push - Pull Processing:
I'm sure most of you are aware that push- or pull-processing can adversely 
effect barcode readability on any film.  The picture area and the edges 
receive the same process.  Therefore, if a cinematographer intentionally 
underexposes two-stops and asks for push-processing, the Keykode and 
human-readable numbers can be up to four times denser than normal.  
However, with manual adjustment, most of the newer readers should be able 
to track the dense barcode.  Going the other way -- thin and faint barcode 
-- makes accurate reading MORE difficult.  Too thin is generally worse than 
too thick.

Barcode on Print and Intermediate Films (IP and IN):
If it's the original Keykode numbers on intermediate film you're after, no 
problem, given normal processing.  Latent edgeprinting on these films 
follows the same tight standards as those for Kodak camera films.  It's 
when print-through Keykode numbers are needed that the rub can come.

Here's where the lab must start playing a more prominent role.  From some 
of the film samples I've seen and heard about, it would appear that the 
rheostats controlling the edgeprint lights on some of the old B&H printers 
haven't been adjusted since these veritable old workhorses were installed 
in the mid-'50s or before.  And some of the optics may not have been 
cleaned since then either.

Negative Cutters:
Neg cutters have suffered for years with marginal edgeprinting, but somehow 
they've learned how to decipher faint and blurry numbers.  Barcode readers 
are not so intuitive.  With more print and master positive being 
transferred, particularly in the features business, good edgeprinting and 
barcode readability have become much more important  We're hoping film labs 
will see the need to improve their edgeprinting.

It's not that difficult, really.  The barcode density range on print can be 
quite wide and still very readable.  Here are some guidelines:
    35mm & 65mm edgeprint - densitometer reading status A red density:
                            Acceptable range  1.3 - 2.5  Optimum  1.9
    16mm edgeprint          Acceptable range  1.8 - 2.6  Optimum  2.2

That's a density range of 800% for 35mm and 65mm edgeprint, and almost 400% 
for 16mm!

More Than Density:
Important as it is, proper density is only one of the factors effecting 
barcode readability.  Uniform exposure, edge contrast, symbol contrast and 
modulation are also very important, whether it's barcode on film or on a 
box of corn flakes.  These ubiquitous elements can be precisely analyzed 
using a screen-capture oscilloscope, reading the waveform output of the 
barcode reader.

If It Looks Good, Chances Are It Is Good:
But, you can learn a lot about good and bad barcode by simply looking at 
the film on a light table with a good loupe.  Is the density of the bars 
fairly uniform across their height, laterally from film edge inward?  Any 
encroaching edge fog?  (Can be particularly troublesome on the tiny 16mm 
barcode.)  Are the edges of the bars sharply defined?  Good contrast 
between bars and spaces?  If there's a lack of contrast, ask the lab to 
read the density of the spaces as well as the bars.  (Density patches 
provided on all Kodak films for this purpose.)  A red density difference of 
1.6 or greater on print is ideal.  However, I've seen good readability with 
less contrast if overall density and other factors are on target.

Further Proof:
We've conducted extensive edgeprint tests at the Kodak R&D labs, commercial 
labs in New York, Virginia and Los Angeles, and determined that Keykode 
numbers imaged on print stock and intermediates can be read over a wider 
range of reader intensities than most original negative.  We've also run 
tests proving that Keykode numbers read well through several generations -- 
IP to IN to print.  In fact, the Kodak Keykode verification films -- 35mm, 
16mm and super 16mm -- have the original Keykode and human-readable numbers 
imaged through three generations.  We had to produce them this way in order 
to create all the picture elements needed to test the accuracy of the total 
system -- barcode reader, proper frame/field digitization and 
frame-accurate film cut lists from video editing systems.

A long dissertation, but one I hope you've found somewhat helpful.  Your 
comments and questions are most welcome.

Don Ver Ploeg

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