Kodak Gray Card Plus

[verploeg at eznet.net]

Art Adams, on the Cinematographers' Mailing List (CML), recently 
questioned the setup values indicated for the Kodak Gray Card Plus. 
"I would expect the black chip to be at 7.5ire and the white chip at 
around 92ire," Art said.  (Instead of 20 and 80, as he was told)

I posted the following response, and thought that this information might 
be helpful to the TIG as well.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The light and dark patches on the Kodak Gray Card Plus, as Geoff 
mentioned, are not solid black and white.  The reflectance of the light 
patch is 90 percent; the dark patch is 3 percent.  The rationale?  

1. These values allow the colorist to more easily and accurately set the 
primary controls of the telecine to the prescribed RGB values when using 
the card as a grading reference.  You're not operating way up on the 
shoulder and down in the toe of the film's characteristic curve.  There's 
room to come at the readings from both sides.

2. Lenses have varying amounts of flare, which can alter the exposure of 
a solid black (velvet plush) more than a value somewhat above black.  At 
3 percent reflectance, flare is less of a factor. 

3. The values of these two additional patches on the Kodak Gray Card Plus 
were also chosen to provide reflectance levels about equidistant from the 
standard 18 percent gray, the main portion of the card.

The suggested RGB setup values for normal exposure of this card are:
          VOLTAGE       IRE
White       0.56         80
Gray        0.32         45 
Black       0.14         20

That's why the Kodak rep told you 80- and 20-IRE.  But as Ed Colman 
mentions, some people feel that these values result in initial grading 
that's too flat.  If so, we suggest numbers more toward 85-50-15.  Of 
course, it depends on the film you're using and the look you're trying 
to achieve.

The two additional patches on the Kodak Gray Card Plus are intended to 
make it a more definitive grading reference, particularly when the card 
is shot as a guide to preserve special lighting, intentionally altered 
exposures or desired grading that may seem inexplicably weird.

However, the card is NOT intended to be a "set it, forget it, let's rock 
and roll" hands off guide to grading.  It's a START grading reference, 
and if shot right, a pretty good one we think.  Particularly for 
unsupervised sessions and those lacking other benchmarks.

For more on this, including the users' guides for all cinematography and 
telecine tools, check out Kodak's WebPages:
http://www.kodak.com/US/en/motion/postProduction/tools/

Don Ver Ploeg
Kodak consultant


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