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What is gray?
Old 12-17-2006, 12:24 AM   #1 (permalink)
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Have you noticed that grAy is the same as grEy? Which is the correct spelling. Some spell it grey and some spell it gray?

Oddly, not even the creators of the HTML and CSS definitions could agree. There are various shades of gray and each has a word in HTML and CSS, but one of the choices is spelled with grey and the others with gray. I'll give you a clue, the one with grey is D3D3D3.

So what is gray/grey in the photographic world? Well a simple definition is that it is not 0 or 255 (black or white) but is in-between these two and it is comprised of equal parts of Red, Green and Blue.

And why do we hear so much about 18% gray? How many people even know what that means? Oh well, we can cover that in the next installment.

Anyway, in thinking these gray thoughts I decided we needed to post some gray images. Now what is a gray image? Well maybe this is a gray image:

Click for larger version
What is gray? 


or perhaps this will leaving you seeing grey:

Click for larger version
What is gray? 


Or perhaps you'll come up with something that is really grey!

Cheers,
rfs
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What is gray?
Old 12-17-2006, 02:43 AM   #2 (permalink)
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Lessee, you're in Dallas/Ft Worth if memory serves me...

If you were in the upper midwest at this time of year, you'd know for certain what color gray, grey, or any other spelling variant of the color is. It's the color of the sky from November till March... and a primary cause of Seasonal Affective Disorder (SAD), and that's a fact Jack!
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Re: What is gray?
Old 12-17-2006, 04:47 AM   #3 (permalink)
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Some of my non-glamour stuff. All three are B&W infrared. The first two were shot with a modified Coolpix 995 and the third is old fashioned Kodak HIE.

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Re: What is gray? 


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Re: What is gray? 


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Re: What is gray? 
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Re: What is gray?
Old 12-17-2006, 09:10 AM   #4 (permalink)
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A question to R_Fredrick_Smith:
Do you have both the Digital Calibration Target and the 24-patch Gretag Macbeth? Do you shoot in RAW?

I have both and I shoot in RAW. As an experiment, under the same lighting conditions, I did the following...
1. Set custom WB using Digital Calibration Target.
2. Shoot image #1 of Digital Calibration Target.
3. Shoot image #2 of 24-patch Gretag Macbeth.
4. In ACR, open image #1 and perform a 1-click WB on the gray part of the target.
5. In ACR, open image #2 and perform a 1-click WB on a gray swatch. (I usually use one of the 2 swatches next to the white swatch)

What I've discovered is that in step 4, the 1-click WB doesn't change the WB much. (Remember, I did a custom WB in-camera prior to shooting image #1). But when I open the Gretag-Macbeth image, the 1-click WB yields a substantially different reading.

And in my opinion, the Digital Calibration Target WB is better than the Gretag Macbeth. Your experience and thoughts?
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Re: What is gray?
Old 12-17-2006, 09:43 AM   #5 (permalink)
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According to "Google Answers", the only difference is between British and American English spellings, to quote:

It appears that the "gray" varient appeared later, as an American
English varient of "grey". Both have mostly the same many meanings:

"gray also grey ( P ) Pronunciation Key (gr)
adj. gray·er, also grey·er gray·est, grey·est
Of or relating to an achromatic color of any lightness between the
extremes of black and white.

Dull or dark: a gray, rainy afternoon.
Lacking in cheer; gloomy: a gray mood.

Having gray hair; hoary.
Old or venerable.
Intermediate in character or position, as with regard to a subjective
matter: the gray area between their differing opinions on the film's
morality.

n.
An achromatic color of any lightness between the extremes of black and
white.
An object or animal of the color gray.
often Gray
A member of the Confederate Army in the Civil War.
The Confederate Army. "

Dictionary.com
[ http://dictionary.reference.com/search?q=gray ]

So yes, "grey" is a color, and was always so. Us Americans had to go
and be different with "gray."


A few meanings are unique, however, to the "gray" varient. For
example:

"gray
n. Abbr. Gy
The SI unit for the energy absorbed from ionizing radiation, equal to
one joule per kilogram."

Dictionary.com
[ http://dictionary.reference.com/search?q=gray ]


You might also find these links interesting:
[ http://flakmag.com/misc/grey.html ]

"Gray" is the American spelling. "Grey" is the British spelling."
[ http://www.artlex.com/ArtLex/g/gray.html ]

Search terms:

Dictonary
grey gray spelling

End of quote,
Doc
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Re: What is gray?
Old 12-17-2006, 09:51 AM   #6 (permalink)
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If I recall correctly, 18% gray is approximately the same color tone as the human skin, with some variations based on how dark or light that persons skin color is. That's based on what a light meter or camera meter would see in black & white.

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Re: What is gray?
Old 12-17-2006, 10:04 AM   #7 (permalink)
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Well, remember, it's Zone V grey, 18% reflectance.

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Re: What is gray?
Old 12-17-2006, 11:34 AM   #8 (permalink)
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Even on the bright and sunny days in the desert there are many shades of gray all over the place.
Carlotta in the desert about 40 miles Northwest of Phoenix

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13% not 18% & a Ringflash? (grin)
Old 12-17-2006, 12:49 PM   #9 (permalink)
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It's been argued and proven scientifically that middle gray is not 18-percent as we've been lead to believe over the years, it's in fact 12- to 13-percent. (source, The National Geographic Photography Field Guide by Peter K. Burian and Robert Caputo, National Geographic Society, Washington DC, 2003)

18% grey is in fact a gray area--

18-percent gray came about from way back when Kodak pushed it as a standard, some rumor because of heavy influence by Ansel Adams, though Kodak now admits that 18-percent gray doesn't accurately mimic a middle-tone and includes instructions in their new gray card kits to adjust your exposure + 1/2 F/stop, or when you do the math, 12.75 percent reflectance when an 18-percent gray card is held at a 45-degree angle reflectance to the camera.

The key here is the angle at which you hold your 18-percent gray card, it must be 45-degrees to the axis of the camera, unless you're lighting an image with a ringflash The camera sees the reflectance at an opposite angle, cos(45degrees) = x/18. which gives you approx. 12.72 degrees.

Someone mentioned Zone 5 in reference to Ansel Adams Zone system is 18-percent gray and the proper way to expose--that's only true for darker skins. Ansel's definition for Zone 5 included it's use to accurately reproduce "dark skin" whereas Zone 6 was for "average Caucasian skin value." Even Adams knew Zone 5, or 18-percent gray was not used for "average" skin.

Even Wikipedia states, "With a slightly revised definition of reflectance, this result can be taken as indicating that the average scene reflectance is approximately 12%," for light meter calibration.

Many sources state that camera meters in fact work at 12-percent reflected light based on averaged metering and depending on the make and model, some cameras come in 10-, 11-, 12-, 13- and even 14-percent flavors while still others use the 18-percent standard, but compensated by software after the reading is taken.

All very technical and if you scour the web you'll find some interesting articles on it, my favorites is from the Photographic Society of America Journal.

One other point, if you really want to check your meter's cabilities, take a solid piece of white card and an identical piece of black card, then go outside in an open shade area. Place your camera on a tripod, set the exposure to "program" or automatic, then photograph each card where it totally fills the frame of the camera--no outside influences and have your meter set to average or matrix. Take a mental note of the exposure values. Then take the same two cards, place them side by side and photograph them and see what you get? All three photos should be gray!

Why, because your camera meter is a reflectance meter and is calibrated to see only middle-gray (11- to 18-percent) and will take that black card and give you the correct exposure to make it gray, same with the white card, to make it grey.

If you took Roger's black, gray, white card combination he posted, and metered through the camera for the black area only (making sure you fill the entire camera frame with black only) then while holding the exposure stepped back and photographed the entire card combination, the gray and white portions of the will reproduce as white while the black is reproduced as middle gray--an overexposed image would look like this on a histogram.

If you did the exact opposite and your reflected meter reading was from the white portion only, white will reproduce gray and the black and gray portions will reproduce black, or the equivalent of underexposed in a histogram.

In the end, it's a very gray area and technical. I highly recommend you throw the technical out, learn to "feel" how you camera operates and "know" your equipment. Even the same make and model cameras and meters will be different from each other as they used a lot of algorithms and "canned" calibrations or programming, making no two cameras or meters alike. Learn what histograms can do for you as they are the "fingerprint" of the scene. Learn to judge your scene and how that should replicate on a histogram pattern--don't be fooled that a histogram has to look like a nice mountain range from end to end. For the record, 11- to 18 percent gray is in the middle area of a histogram.

Note to Roger: The McBeth ColorChecker™ Color Rendition Chart you posted is misleading when you lable it as "...Custom White Balance set with a Gray Card." When I first look at that image with that label on the top it makes it look like you're saying that is a gray card. It's not, the McBeth is from the film days with densitometers. While it's easily adapted for today with a known white-point and black-point reference for Photoshop, it's not a gray card, it's a color scale with gray patches and I would never use it for white-balance. Keep in mind, even though you can get gray to be gray if you photographed that card and ensured your densitometer in Photoshop showed equal RGB values (128,128,128) for gray, depending what color space your shooting in and what color space is your working space in Photoshop, the other colors will reproduce differently, or show different color values in the RGB densitometer.

Here's to clear skies, wishing everyone a Happy Holiday season, rg sends!
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13% not 18% & a Ringflash? (grin) 
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Re: 13% not 18% & a Ringflash? (grin)
Old 12-17-2006, 03:21 PM   #10 (permalink)
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Quote:
Note to Roger: The McBeth ColorChecker™ Color Rendition Chart you posted is misleading when you lable it as "...Custom White Balance set with a Gray Card." When I first look at that image with that label on the top it makes it look like you're saying that is a gray card. It's not, the McBeth is from the film days with densitometers. While it's easily adapted for today with a known white-point and black-point reference for Photoshop, it's not a gray card, it's a color scale with gray patches and I would never use it for white-balance. Keep in mind, even though you can get gray to be gray if you photographed that card and ensured your densitometer in Photoshop showed equal RGB values (128,128,128) for gray, depending what color space your shooting in and what color space is your working space in Photoshop, the other colors will reproduce differently, or show different color values in the RGB densitometer
I was using an image that was part of an article that I did some time back. I did not use the Color Checker to create a white balance, but rather used a gray card and set the camera to the custom white balance setting using the photo of the gray card as the reference photo. I then photographed the Color Checker card using that custom white balance setting. I then repeated the same thing where I set the CWB using a White card and then I photographed the Color Checker card again. Both photos of the color checker card were identical. I doubt you could actually use the Color Checker card to do a CWB since the gray and white swatches are too small to fill the partial metering circle unless you were using a macro lens and then you would probably be blocking the light. When I want to set CWB I just use the same Black/Gray/White target and make sure the gray area fills the partical metering circle of the camera.

Where the color checker card really comes in handy is when one wants to calibrate their RAW conversion software.

Thanks for the notes on the 18% gray. I was going to cover some of that material later on, but no need now. There has been a long controversy over what color a gray card should be (12%, 13% 14%, etc). I've seen lots of articles both pro and con on the subject. But I've generally found that between 12 and 13% seems to be a better working gray than 18%.

Another interesting note about gray cards in general is that they can make excellent reflectors. Based on the 90% rule, you can develop a number of rules about gray as a reflector. Each shade of gray reflects/absorbs a certain percentage of light and does not add a color cast to it. It is thus possible to use various shades of gray to do very subtle tonal shading. I use this quite a bit for product type photography. So the 18% gray card will reflect 18% of the light that hits it which means it is 50% as bright as a white sheet of paper.

Cheers,
rfs
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