Gray Card? 18%? Or something else?

[prodigy2k7]

On another forum I found this quote:

"Most of what Karl said is exactly right, but meters don't measure to 18% gray. 18% gray is for printers, light meters measure to 12% gray."

Wait, whaaa???
I've always heard 18%, never 12%.

Meters Don't See 18% Gray by Thom Hogan

 

[KmH]

Is that in reference to in-camera light meters or hand-held light meters?

At any rate the % gray is not as important as the gray part is.

 

[Green Li]

I actually prefer using white balance discs

 

[prodigy2k7]

Is that in reference to in-camera light meters or hand-held light meters?

At any rate the % gray is not as important as the gray part is.

erm, can you elaborate?

 

[Josh66]

I actually prefer using white balance discs

For setting your exposure?

 

[xjoewhitex]

I actually prefer using white balance discs

For setting your exposure?

Which are we even talking about? lol Exposure or w/b?

 

[Josh66]

I actually prefer using white balance discs

For setting your exposure?

Which are we even talking about? lol Exposure or w/b?

Well, the OP was talking about meters, so I would assume that we're talking about metering and exposure.


That's one of the reasons I like grey cards more than WB disks - it can be used for both.

 

[xjoewhitex]

For setting your exposure?

Which are we even talking about? lol Exposure or w/b?

Well, the OP was talking about meters, so I would assume that we're talking about metering and exposure.


That's one of the reasons I like grey cards more than WB disks - it can be used for both.

But isn't it a meter that measures the light temperature? lol Hmm im bored. But I also agree, the expo disc seemed to be a pretty nice gizmo but I prefer grey cards.

 

[Josh66]

Well, it's a meter of some kind, but not the same one the OP is talking about.

 

[Big Mike]

From what I've heard...the choice of using 18% grey (many years ago) was both scientific and political...with many people arguing many point. I believe that 18% grey is exactly half way between black & white, so it is maybe an obvious choice.

However, after further (more recent) evaluation. The 'average' scene is closer to 12% grey (your mileage may vary). So camera companies are adjusting what their meters are calibrated it.

As mentioned, it doesn't really matter what the exact value is...as long as the photographer has an idea of how reflected metering works and and is somewhat familiar with their gear. Because in the grand scheme of things, the metered value (without compensation) is just your 'working exposure'...not the 'correct exposure'.

On top of all this, fancy camera metering is getting pretty complex. Cameras are starting to recognize things in the frame and use those for metering. For example, I thin some cameras with face recognition technology, are also using the faces for metering, rather than just blindly taking the whole scene (or just the centre) into account. And if I'm not imagining hearing this, I think that some recognize things like green grass & blue sky...and can take that into account.
In other words, there is a lot R&D being spent in this area, because it means better photos for the point & shoot crowd...which is MUCH larger (and more lucrative) than the 'photographer' crowd.

 

[KmH]

Is that in reference to in-camera light meters or hand-held light meters?

At any rate the % gray is not as important as the gray part is.

erm, can you elaborate?

Hand-held meters can usually meter reflected, incident and strobed lighting.

In-camera meters can only meter reflected light.

In-camera light meters are calibrated differently than hand-held meters, because unlike hand held meters, in-camera meters have a variety of reflected light metering modes - Spot, center-weighted, and Matrix/Evaluative.

Gray is equal amounts of RGB, so there is no color cast. White and black are just the extreme limits of gray.
White is R=255, G=255, B=255 (0% gray)

18% gray is R=209, G=209, B=209.

50% gray is R=128, G=128, B=128

Black is R=0, G=0, B=0. (100% gray)

Any tone having equal amounts of RGB are gray.

 

[Pgeobc]

Big Mike is more to the point: scenes defined as typical, integrate to 12-12.5% gray and that is what light meters are calibrated with, mostly. 18% gray is the closest and is, as noted, half-way in the scale. The difference is about a half stop and years ago, Kodak advised using a half stop compensation for some types of gray-card measurement. Kodak formerly made a little photo guide that had all sorts of good information in it: color correction charts for use with filters, flash power and guide number estimates, etc. It also had a complex chart that detailed the best ways to use gray cards with incident light meters.

 

[Helen B]

...
Gray is equal amounts of RGB, so there is no color cast. White and black are just the extreme limits of gray.
White is R=255, G=255, B=255 (0% gray)

18% gray is R=209, G=209, B=209.

50% gray is R=128, G=128, B=128

Black is R=0, G=0, B=0. (100% gray)

Any tone having equal amounts of RGB are gray.

It's confusing, isn't it.

An '18% grey card' is an 18% reflectance grey card - so pure white (if it existed) would be 100% on the same scale, not 0%. There are few real world 'whites' brighter than 96% reflectance and most are 85-92% or thereabouts. '18% reflectance' means that it reflects 18% of the light falling on it (compared to a theoretically perfect diffuse reflector, measured at 45 degrees with the light beam arriving perpendicular to the surface). That means that it is not a 50-50 mix of black and white. It is what we perceive as roughly middle grey with our logarithmic response to brightness. It's usually represented as R=G=B=112 to 120 (depending on the tone curve) on a 0-255 scale or L=50 in Lab.

Very early grey cards for photographic use (late 1930's) were 14% reflectance. This was arrived at by comparing metered exposures of many different types of scene with exposures made with grey cards of various reflectance. The best correlation occurred at 14%.

Best,
Helen

 

[table1349]

Guess I will toss my 2 cents in here. I use a 12% gray target these days. Not because the meter doesn't read 18% gray but rather sensors don't place 18% gray in the middle of a histogram due to the way sensors are calibrated. I don't profess that this is absolute truth but I have been happy with the results.

From Lastolite:
The EzyBalance 12% is similar to the original EzyBalance but features a 12% grey rather than the original 18% grey. Many photographers now use a 12% grey as their midtone reference when calibrating their camera before they start shooting. This compensates for the camera’s factory calibration settings and positions the midtone spike on the histogram in the centre position rather than slightly off to one side.

Lastolite Limited, Manufacturer of Portable Photographic Studio Systems.