Where does 18% gray originate (Page 2): Some interesting links - 12% http://www.bythom.com/graycards.htm...

jerryc41 Loc: Catskill Mts of NY

wjones8637 wrote:

A while back there was a discussion where a graph showed that an 18% gray card reflected 50% of the light falling on it. This makes sense, since it is used for setting mid tones. My question is where did the 18% originate? Is this the percentage of a pure black pigment mixed with a pure white pigment?

A curios mind had time to wander.

Thanks,
Bill

Some interesting links -

12%
http://www.bythom.com/graycards.htm

http://digital-photography-school.com/how-to-use-a-gray-card-to-get-more-accurate-exposures-and-color/
http://www.digitalphotomentor.com/how-to-use-a-gray-card-for-custom-white-balance-and-metering/?utm_source=Digital+Photo+Mentor&utm_campaign=f5fb80c5b2-DPM_Blog_Broadcast&utm_medium=email&utm_term=0_ec33f1d0c3-f5fb80c5b2-263056661&mc_cid=f5fb80c5b2&mc_eid=fddc3ab094

Shirley Card
http://www.npr.org/2014/11/13/363517842/for-decades-kodak-s-shirley-cards-set-photography-s-skin-tone-standard

nekon Loc: Carterton, New Zealand

Yes, back in the 1950's Kodak stated that all exposure systems were calibrated at 12.9% grey, rather than the normally quoted 18%

camerapapi Loc: Miami, Fl.

An 18% gray card reflects exactly 18% of the light falling on it. I am not so sure where the 18% or middle gray originated. Those that have investigated into this matter believe that 12% reflectance is more accurate but I do not have all the information.
In the particular case of digital 18% reflectance is slightly off.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

wjones8637 wrote:

A while back there was a discussion where a graph showed that an 18% gray card reflected 50% of the light falling on it. This makes sense, since it is used for setting mid tones. My question is where did the 18% originate? Is this the percentage of a pure black pigment mixed with a pure white pigment?

A curios mind had time to wander.

Thanks,
Bill

The answer is in this article penned by Thom Hogan a while back:

http://bobd.tv/files/Mid-gray.pdf

FotoHam

The geometric mean between 90 and 3 is 16.4, not 18.??

robertperry Loc: Sacramento, Ca.

Here is what I learned back in college photo classes. The sun produces 100% light, 18% of this light is reflected off of all objects, which allows us to see.

nadelewitz Loc: Ithaca NY

wjones8637 wrote:

A while back there was a discussion where a graph showed that an 18% gray card reflected 50% of the light falling on it. This makes sense, since it is used for setting mid tones. My question is where did the 18% originate? Is this the percentage of a pure black pigment mixed with a pure white pigment?

A curios mind had time to wander.

Thanks,
Bill

18% gray is the AVERAGE of the brightnesses contained in a "normal" scene ranging from highlights to shadows. It simply means the card is reflecting 18% of the light hitting it.

The 18% shade can be produced by mixing black pigment and white pigment (paint, printing ink, etc.), of course. Also by calibrated exposure and developing of a silver-halide emulsion on paper.

NatureRocks

Howard5252,
Your comment about blind people working for Kodak prompted recall of one of Dimitri Martin’s cartoons: a sign before a wide expanse, reading “scenic Vista,” beneath which were Braille bumps...

bleirer

robertperry wrote:

Here is what I learned back in college photo classes. The sun produces 100% light, 18% of this light is reflected off of all objects, which allows us to see.

bleirer

FotoHam wrote:

The geometric mean between 90 and 3 is 16.4, not 18.??

I was rounding, whatever the exact value of white paper and black ink is. Could probably look it up, but the point is the same.

EDIT: 3.5% and 95%, see how those compute!

Doc Barry Loc: Huntsville, Alabama USA

rfreudenheim wrote:

It’s the color of the sky in Rochester, NY (home of Kodak) :)

I agree, if you mean in Decembers. 😁. I’m a graduate of he U of R and remember the bets made on how many minutes of sunshine would be observed in December. Zero often won!

Photec

Wallen wrote:

The reality is that this is just a guide preferred... (show quote)

One thing every (old zone system) film photographer who has transformed to digital RAW photography will agree on, getting desired images is SO much easier and quicker. The other advantage is that the darkroom being digital smells much better!

Dale Evans - Amaetur Loc: Baton Rouge, La

When I first started taking pictures, B&W of course, I quickly learned that all white objects would print grey and the way to avoid this was to expose using a grey card, and the snow would be white instead of grey.
I did not care why it worked and that was all I cared about.
Light meters see pure white as 18% of the total signal their sensor sees and will meter an 18% grey card as pure white.

bleirer

Dale Evans - Amaetur wrote:

When I first started taking pictures, B&W of course, I quickly learned that all white objects would print grey and the way to avoid this was to expose using a grey card, and the snow would be white instead of grey.
I did not care why it worked and that was all I cared about.
Light meters see pure white as 18% of the total signal their sensor sees and will meter an 18% grey card as pure white.

I think I get the gist of what you are saying, but I think cameras read grey cards as grey.. I think they are actually set to read 12-13% as middle grey so we are protected from overexposure by a half a stop if we use an 18% card or we can crank up the half stop in compensation.

Dale Evans - Amaetur Loc: Baton Rouge, La

bleirer wrote:

I think I get the gist of what you are saying, but I think cameras read grey cards as grey.. I think they are actually set to read 12-13% as middle grey so we are protected from overexposure by a half a stop if we use an 18% card or we can crank up the half stop in compensation.

Grey cards are for setting the color balance, not the exposure. ASA100@f8x125 second will always give you a good daylight exposure but it will not the correct color balance. A grey card is the best way to do that.

I learned about using grey cards after wasting a 4 hour drive to the mountains to shoot some snow scenes.
I was shooting ASA100 B&W film and used the camera meter. When I made my contact sheet all of the exposures were spot on but the snow was grey instead of white.