I'm a little confused about gray cards

[fs_tigre]

Hi,

I’m a little confused about the Gray Card. I recently read the book understanding exposure and he was talking about using a 18% gray card to get your exposure so, I decided to buy one and I started searching in the forum and I realized that there are two different types one for WB and one for exposure.

Can someone recommend me one that can do both or what are you guys using (the histogram etc.)?

Thanks

[PhotosGuy]

I have several & don't use them anymore since I went to RAW & digital. Try this:
Need an exposure crutch? (http://photography-on-the.net/forum/showthread.php?t=89123)

Gray Card…White Paper. What’s best? (http://photography-on-the.net/forum/showthread.php?t=58677)

[fs_tigre]

First of all thank you for your reply.

The reason I wanted to buy one is because I was reading Understanding Exposure and the author actually talks about it.

So it looks like I wont need one since I also shoot RAW right?

Thanks a lot!

[technodunce]

Why he says you don't need one if you shoot raw is because you can make any corrections now easily in photoshop. Before, particularly if you were shooting slide film you had to have your exposure and white balance perfect in camera because it was almost impossible to fix afterwards.

However, its not a bad idea to understand what grey card is, and what the white balance card he was talking about is.

If you have started using photoshop you will probably learn. Eg in photoshop when you edit your pictures in camera raw, there are some options to correct your white balance. One of them is the custom choice. You get the dropper tool, click on a part of your image which represents a light neutral grey (just like the colour of the white balance card) and if you click on it, the whole image is corrected to that neutral grey.

White balance fixes colour casts in case you didn't get that already.

The 18% grey card is something else. Its like the middle tone for exposure. You light metre will try to render your over all exposure to this shade. Its important to get the highlights and shadows pegged correctly. Its not about colour casts.

So that's why you can't have the both in the same card. I don't know exactly why the white balance card has to be a light grey but it does, it seems. Possibly because its easier to detect colour cast on a lighter shade of grey.

You should be able to buy one in a photograhic shop. Some books you buy have them. When i bought photoshop elements, i also bought scott kelby's book and in the back there were both cards. I used them intially just as I was learning how to use my first DSLR and now I have stopped using them as its easier to fix these things in photoshop.

And i have found other ways of getting a fairly accurate exposure. i don't worry about white balance until i am editing.

[Wilt]

Some gray cards can be used to set exposure, but are NOT NEUTRAL to set White Balance
Some gray cards are neutral and can be used to set White Balance, but are NOT 18% gray to set exposure
Only a few products can be used to set both WB and exposure!


White balance and exposure...

Photovision....http://www.photovisionvideo.com/store/CTGY/DCT/

Douglas grey card...http://www.photo-software.com/greycard.htm

Lastolite...http://www.lastolite.com/ezybalance.php

Sometimes perfect reproduction of White Balance does NOT need to be achieved, and an aesthetically more pleasing rendition might come with NOT having perfectly neutral white balance.

[RDKirk]

So that's why you can't have the both in the same card. I don't know exactly why the white balance card has to be a light grey but it does, it seems. Possibly because its easier to detect colour cast on a lighter shade of grey.

Some gray cards can be used to set exposure, but are NOT NEUTRAL to set White Balance Some gray cards are neutral and can be used to set White Balance, but are NOT 18% gray to set exposure Only a few products can be used to set both WB and exposure!

This is all technically true, but as a practical matter in most uses, you can use most 18% gray cards for both purposes.

White balancing is best done on a card that is guaranteed to have a flat spectral response under all light sources--some 18% cards do, some don't. However, the coloring layer of any brand-name card has a flat enough spectral response in all but the most challenging light--like sodium vapor lights. To say those cards are unusable is like saying daylight balanced film can only be used between 11am and 1 pm in open sun.

And even that restriction is for a custom white balance with JPEG. If you're shooting RAW, any gray card is certainly close enough. If your requirements are very critical, you should be shooting RAW and including the card in the scene as a color balance target.

Ideally, custom color balancing is better done on a light gray card than either white paper or a very dark card because lighter gray is more toward the center of the camera colorimeter's range--and most meters are more accurate at the center of their ranges than either end. But 18% is not so far off center to make a practical difference.

We can expect the people marketing the cards to make the most of every distinction, but in practicality, it doesn't make that much difference until you get into extreme situations.

Sometimes perfect reproduction of White Balance does NOT need to be achieved, and an aesthetically more pleasing rendition might come with NOT having perfectly neutral white balance.

With human beings, this is almost always true. Most humans prefer to appear slightly warmer than they really are. The only clear exceptions I can think of at the moment are babies and geishas.

[Wilt]

RDKirk, I won't dispute your 'retort' because all of photography is not always 'precision'. The point of my post was not so much to dictate axioms or rules, but to educate buyers that all 18% card are not perfectly neutral (I have one myself, so I know!) and not all gray surfaces for white balance are necessarily at 18% gray...providing awareness, not preaching hard dogma.

[Digital_zen]

The problem of understanding gray cards is only exasperated by the fact that the ANSI standards to which most manufacturer's meters are calibrated aren't set-up for 18% gray at all but closer to 12% gray.
While this doesn't help with WB, it does raise some questions as to why the myth 18% being medium gray to our meters, persists.
Here's a link to an article about it. http://www.bythom.com/graycards.htm

[Wilt]

The problem of understanding gray cards is only exasperated by the fact that the ANSI standards to which most manufacturer's meters are calibrated aren't set-up for 18% gray at all but closer to 12% gray.
While this doesn't help with WB, it does raise some questions as to why the myth 18% being medium gray to our meters, persists.
Here's a link to an article about it. http://www.bythom.com/graycards.htm


And readers should note that there are two VARIABLES that the meter manufacturer can choose to set, yet still adhere to the ANSI/ISO standard fully!

the equation in the ANSI standard:
2^EV = A^2/T = BS/K = IS/C

EV equals exposure value
T = effective exposure time in seconds
A = actual f-number of lens diaphragm
S = ISO/ANSI speed of film (not the old DIN degrees)
B = field luminance in footLamberts
K = exposure constant (reflected light)
I = incident light in footcandles (illuminance)
C = exposure constant (incident light) where the ISO standard gives the value of C as 30 +/- 5.

Per ISO 2720:1974, "the constants K and C shall be chosen by statistical analysis of the results of a large number of tests carried out to determine the acceptability to a large number of observers, of a number of photographs, for which the exposure was known, obtained under various conditions of subject manner and over a range of luminances."

After some more math in the standard, the value of K is derived as 3.64, assuming that C = 30. Assuming that C = 30 and K = 3.64, at the ratio of K/C is 3.64/30 or 12.3%. But not every manufacturer uses C = 30 !

ISO 2720:1974 recommends for reflected light meters to use a range for K of 10.6-13.4 cd/m² luminance. Two values for K are in common use: 12.5 (Canon, Nikon, and Sekonic[1]) and 14 (Kenko[2] and Pentax); the difference between the two values is approximately 1/6 EV. With a hemispherical receptor on an incident meter, ISO 2720:1974 recommends a luminance range for C of 320-540 lux; values typically are between 320 (Minolta) and 340 (Sekonic).

To repeat, NOT ALL MANUFACTURERS assume the same value for the same constants. Meters provide a guide to 'proper exposure', no more no less. Shutter speeds can deviate from stated values, apertures can deviate from stated values, optical transmission is typically not 100% but can vary from lens design and coatings to lens design and coatings. And digital cameras themselves can vary in sensitivity from stated ISO sensitivity values!


It is the responsiblity of every photographer to evaluate meters and gray cards, to understand what is necessary to correctly reproduce such standard targets as the MacBeth Color Checker accurately in the final print, factoring in the variables of the meter and shutter speed and aperture and light transmission and the calibration of the sensitivity of digital sensor.

[fs_tigre]

Thank you all!

[fs_tigre]

As I said I have been reading Understanding Exposure and the author shows how to get the right exposure using the brother sky, green areas, blue jeans brothers and he actually mentions the gray card, and here is where I'm confused he is using all these techniques to find the right exposure but he also mentioned that the whites are going to be more white, so I'm asking my self if you already found the right exposure using these techniques with the whites looking white, I'm assuming you found the right WB at the same time and no need to adjust your WB in PP if you are shooting RAW and if you are shooting .JPEG your WB will be just find, is this correct or the withes will still need to be adjusted either in PP or at shooting time?

Can some be so kind and explain this a little bit more?



By the way, try the "Shoot to the Right" (http://photography-on-the.net/forum/showthread.php?t=89123) technique to find your exposure, it is simple and it works.

Thanks

[PhotosGuy]

here is where I'm confused he is using all these techniques to find the right exposure but he also mentioned that the whites are going to be more white, I think he's talking about brightness & not color balance? I'm assuming you found the right WB at the same time and no need to adjust your WB in PP if you are shooting RAW and if you are shooting .JPEG your WB will be just find, is this correct or the withes will still need to be adjusted either in PP or at shooting time? Don't assume. Post #17:
http://photography-on-the.net/forum/showthread.php?t=753008

[fs_tigre]

I see your point there is no perfect WB for every photo, put what if you are shooting JPEG where you don't have the option as with RAW and you really want to be as close as possible to the right WB?

Thanks

[Wilt]

I see your point there is no perfect WB for every photo, put what if you are shooting JPEG where you don't have the option as with RAW and you really want to be as close as possible to the right WB?

Thanks

You apparently missed the point raised that 'the right WB' is not the same as 'the best WB for the shot'.

Post processing software does permit JPG files to be altered in warmth (WB) quite a bit. (This shot RAW, but the JPG only was manipulated for WB variants.
http://i69.photobucket.com/albums/i63/wiltonw/IMG_2543-cool.jpghttp://i69.photobucket.com/albums/i63/wiltonw/IMG_2543-neutral.jpghttp://i69.photobucket.com/albums/i63/wiltonw/IMG_2543-warm.jpg

[krb]

what if you are shooting JPEG
"Hey Doc, it hurts when I do this..."

Why not just shoot in RAW?

[fs_tigre]

Thank you all very much!

I started reading the newest book from Bryan Peterson and he kind of answered my question about WB in this book.