Comments on: DIY Grey Card

By: carlo ballestrero

carlo ballestrero — Sat, 07 Mar 2009 08:08:58 +0000

The meter reads the light reflection, not the colour. So readings are greatly influenced from the smoothness of the paper (and the angle of incidence of light on the greycard, of course).
So it will be difficult to check an homemade greycard without a true greycard or a professional incident-light meter.
Better to read a simple white matt paper and substract -2, 1/3 f : it’s exactly the same.

carlo – again

By: carlo ballestrero

carlo ballestrero — Sat, 07 Mar 2009 07:41:35 +0000

The grey colour on a Kodak Greycard is a 50% grey (50%K).
18% is the amount of light reflection of a 50% grey. That’s why greycards are called 18% grey, and why you may achieve good results setting 127 -127 -127 in your bitmap file (50% K, if converted in B&W). More or less is only a matter of your printer.

hope this helps.
carlo – professional photographer

By: raymond

raymond — Wed, 03 Dec 2008 02:00:09 +0000

That’s what I would have thought — but what I read, and what my actual print-and-shoot tests tell me, is 118. Strange but (apparently) true.

By: Kai Klein

Kai Klein — Mon, 01 Dec 2008 07:51:41 +0000

I may be wrong or miss some fundamentals, but for me a 18% Grey calculated on 8 Bit RGB Values would be: 255*0.18 = 45,9 not 118 or 128 which is 46% and 50%.

Kind Regards

Kai