Kodak’s gray card

RH
Posted By
Ronald_Hirsch
Jan 4, 2004
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944
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6
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Closed
Is a Kodak gray card a "known" value in terms of RGB numbers? Through the years, I have had various Kodak gray cards, and many of them looked a lot darker/lighter than the others. Maybe they changed color inside a light proof envelope – I don’t know.

But, I often do color correction using a 3 color card – black, white, and gray. The black and white are pretty good – black velvet, and ultra bright inkjet paper. But, the Kodak gray area is hard to evaluate.

Is there such a thing as a calibrated gray card, where the RGB values are a known quantity?

With my 3 color card, using channels, I can color correct most any off-color image where the card was present in the image. I can actually get by not knowing the real RGB of the gray, but I’d like to do things as carefully as I can.

Ron Hirsch
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Pierre_Courtejoie
Jan 4, 2004
I don’t think that you could use an RGB value since the numbers will vary following your profile… (you can see a good example in this thread):

< http://www.photoshoptechniques.com/forum/showthread.php?s=&a mp;threadid=5952>

One of the only ways to reliably quantify it might be to use LAB values…
PH
Photo_Help
Jan 4, 2004
I would guess it is a 50% gray in Photoshop. Kodak calls it 18% (based on the light it reflects).

Color Correction Using a Gray Card < http://www.bradhinkel.com/Color%20Correction%20using%20a%20g ray%20card.htm>

Tips on taking pictures using a gray card. <http://pixels.homestead.com/Tips.html>

"Meters Don’t See 18% Gray <http://www.bythom.com/graycards.htm>"

Disclaimer: I am not a photographer, this information is based on a quick Google search.
LH
Lawrence_Hudetz
Jan 4, 2004
"Meters Don’t See 18% Gray"

Interesting reference to Adams. Finally, I know why he always decreased the film speed by at least 1/2 stop. And I also now know why I didn’t!
J
Jim
Jan 5, 2004
My scanner reported 128, 128, 128 using AdobeRGB.
Jim
wrote in message
Is a Kodak gray card a "known" value in terms of RGB numbers? Through the years, I have had various Kodak gray cards, and many of them looked a lot darker/lighter than the others. Maybe they changed color inside a light proof envelope – I don’t know.

But, I often do color correction using a 3 color card – black, white, and gray. The black and white are pretty good – black velvet, and ultra bright inkjet paper. But, the Kodak gray area is hard to evaluate.
Is there such a thing as a calibrated gray card, where the RGB values are
a
known quantity?

With my 3 color card, using channels, I can color correct most any
off-color
image where the card was present in the image. I can actually get by not knowing the real RGB of the gray, but I’d like to do things as carefully
as
I can.

Ron Hirsch

J
Jim
Jan 5, 2004
"Jim" wrote in message
My scanner reported 128, 128, 128 using AdobeRGB.
Jim
Alas, this is incorrect.

I photographed a gray card with Fuji Provia 100F. A scan of the slide showed these values in the sRGB
color space:

R 125
G 124
B 130

The values should be 128, 128, and 128. As you can see, there is a very slught blue cast to the image.

A scan on the gray into my old flat bed scanner yielded a very very unusable image. I don’t have either the image
or the scanner around for further checking.

Jim
MG
Miguel_Garcia
Jan 5, 2004
You can try this company. Does well for us…

Robin Myers Imaging – www.rmimaging.com – DGC-150 Digital Gray Card

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