Grey Cards

blackwaterstudio

Does anyone know the R.G.B.values so that you can print out your own grey card using photoshop, to use in setting custom white balance.Grey cards proper seem so expensive for what is after all a colored piece of paper.

I know I'm cheap, but since we have other "cheaper" ways of doing things, lighting, etc I thought this might be a interesting point.

Shay Stephens

A long winded way of saying 117,117,117
You can't produce a calibrated gray card without a standard to work from. You would spend more in paper and ink than you would if you just bought a gray card:
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=231564&is=REG

But if you are interested in the academic aspects of it, middle gray has an RGB value of 128,128,128 and it reflects 18% of the light that hits it. But that is not the only thing you need to consider. The computer you use has a particular gamma value that you need to also consider. In the case of PC's the gamma is typically 2.2 and I believe Macs use 1.8. David Rosenthal provided me a while back with a formula to use in producing a particular gray value from a printer
(reflectance to the power of the gamma ratio) multiplied by the full range of possible grayscale values:
(0.18 ^ (1.0 / 2.2)) * 255 = 117

For a PC it would go something like this:
The amount of reflected light = 18% or .18
The gamma ratio = 1.0/2.2 or .454545
the amount of reflected light (.18) to the power of the gamma ratio (.454545) = .459
.459 multiplied by the full range of grayscale values (255) = 117

So if you have a printer that prints correctly using the same gamma as your computer, you should be able to get a working grayscale target using an RGB value of 117,117,117.

In my own tests, I have seen numbers within +10% of this that still work within 1/3 of a stop. Setting WB is also fairly accurate as long as you use black ink only for the printing. This was probably two years ago. Modern printers and inks may do better now.

But it is still easier I think to just buy a card and not have to worry about water damage or possible inconsistent results. I especially like the plastic cards (they last longer), though they can be somewhat hard to find.

jdsphotography wrote:

Does anyone know the R.G.B.values so that you can print out your own grey card using photoshop, to use in setting custom white balance.Grey cards proper seem so expensive for what is after all a colored piece of paper.

I know I'm cheap, but since we have other "cheaper" ways of doing things, lighting, etc I thought this might be a interesting point.

blackwaterstudio

Thanks for the reply Shay. So many of us have to find cheaper ways to produce things, just as lighting, etc It just hit me to try it. I will most likely end up getting a grey card from somewhere like B&H it just hit me as to how hard it would be to produce one yourself.

patch29

Grey cards are cheap compared to Gretag-Macbeth Color Checker Charts. The now make a grey scale one that would be very useful for digital photographers.

Precise color capturing and reproduction begins with an optimal color balance.**Use the GretagMacbeth ColorChecker Gray Scale card as the first reference shot in a series to easily correct image color by balancing on the mid tone gray value. This three step gray scale (white, 18% gray and black) provides reference values that can quickly be checked and used to adjust colors within most common photo processing software packages.**The GretagMacbeth ColorChecker Three-step Gray Scale card lets photographers quickly adjust colors for shots under most light conditions.**For the studio photographer, the GretagMacbeth ColorChecker Three-step Gray Scale card lets them quickly set up the proper studio lighting ratio between main and fill lights for capturing accurate color without a lot of after-the-fact manipulation.


The GretagMacbeth ColorChecker Three-step Gray Scale card is a full size version of the white, 18% gray and black reference square used in the standard 24-patch ColorChecker.**This target is scientifically engineered to provide a precise uniform surface that is spectrally neutral (reflects equal amounts of red, blue and green) in all types of light conditions. The photographer can now have confidence that the camera’s image is as close to real life as possible.

or their Digital CC which sells for $280.00