Talk:Gray card

Spelling

Isn't it spelled graycard? --Thomas Ploeger 18:38, 27 May 2006 (UTC) That depends whether you speak British or American English. THe normal UK spelling is "grey" although I believe that "grey" and "gray" are both acceptable on both sides of the Atlantic.

This page was requested and I created it - Kodak's preferred naming and spelling is "gray card" (two words, with an A, not an e). I am new here, and don't know how to change the title now that it's created. Furthermore, I will be adding references in the near future. C.anguschandler 05:27, 2 January 2007 (UTC)

I'll move it for you. Dicklyon 06:09, 2 January 2007 (UTC)

Caucasian skin?

Where does this idea of caucasian skin come from? My reading of books suggests that caucasian skin is at least twice as reflective as the 18% card: The Complete Guide to Night & Low-Light Photography. Dicklyon 06:09, 2 January 2007 (UTC)

It comes from Ansel Adams. See "The Negative"; he states Caucasian skin is Zone VI. User:Lexort 20060210.

Does he connect Zone VI to an 18% gray card? This site says skin and zone VI is lighter than the gray card: [1]. Dicklyon 04:49, 21 January 2007 (UTC)

I don't have the book handy any more, but my memory is that he says that skin is VI, and V is 18% reflectivity,and VI is 36% (with VII 72%). This seems clear enough to me - the obvious hard part is that every individual's skin is different. I have had success spot metering on skin with -1 exposure compensation. User:Lexort 20060121T0456Z

Is there any good reason to have a comment about skin of any sort? That's really about the zone system and out of place here. I would like to delete the whole sentence and then this talk section. Lexort 05:05, 21 January 2007 (UTC)

There was a reason when it was thought to be 18%. Since that was wrong, there's no reason left, and I took it out. Dicklyon 05:16, 21 January 2007 (UTC)

18% grey has nothing to do with skin tone!! And Adams puts the 18% card in zone V, not zone VI (where he says skin tone is). Zone V should be discussed in the zone system, but not so much with grey cards (except zone V). Myndex (talk) 03:08, 13 April 2019 (UTC)

Limitations?

And I don't understand the limitations section at all. The gray card works in general for setting the exposure of a scene such that objects come out with sort of normal brightness in the image. It doesn't matter if some of them are skin of one or another color. The gray card is also not useful for getting color accuracy, just color balance. A color chart provides no advantage over a gray chart for color balancing, but it could be useful for color accuracy if you system has enough adjustments. It would be best to find a good publication and say what is verifiable, instead of making this stuff up. Dicklyon 06:17, 2 January 2007 (UTC)

Some real limitations not discussed in the article (taken from Myers): limitations due to material (paint and ink aren't mentioned in the article), too much reflectivity in the red-to-near-infrared, discolouration and degradation due to heat, bluing and fading due under ultraviolet light, gloss, polarisation and durability. — Preceding unsigned comment added by 77.61.180.106 (talk) 14:10, 29 November 2021 (UTC)

More info

It was my impression that good gray charts are painted with spectrally neutral paint, like the neutral squares on the macbeth color checker, not just printed with a neutral color.

Here's a painted one. And a solid plastic one. Here's where you find the actual size and reflectances of the Kodak Gray Card Plus; and find the Kodak gray card sizes here. Dicklyon 06:27, 2 January 2007 (UTC)

Here's another [http://www.amazon.com/Adorama-Delta-Gray-Cards-Exposure/dp/B00009R838/ref=pd_lpo_k2_dp_k2a_3_txt/002-5363476-1261628 painted one]. Dicklyon 06:32, 2 January 2007 (UTC)

Yes, a proper gray card should be as spectrally neutral as possible. the Munsell N series are all pretty flat, but do drop off in the deep red to infrared area. BTW, "Middle Grey" cards are variously 12% to 20%, depending on the application/use/color system. For instance Munsell N5 is 19.77%. 18.4% comes from CIEXYZ which maps to CIELAB L* = 50.0, and Kodak over the years had many cards for lab aim density that were not 18%, but more typically 14.6 to 16 ish.Myndex (talk) 03:11, 13 April 2019 (UTC)

@solid plastic one: Robin Myers doesn't sell that particular product any more; the conservation target he sells costs $100 and even though I've read his paper on grey cards and I'm sure he knows what he's talking about, I wouldn't be willing to shell out that kind of money for something that doesn't have an online spec sheet. — Preceding unsigned comment added by 77.61.180.106 (talk) 13:43, 29 November 2021 (UTC)

@Amazon: Going by the reviews, those are crap. (I note that half the reviews are 5 stars, but they don't seem genuine when I read them. I don't use Amazon myself, does it have a bot problem?) People are complaining about the manufacturing quality and their reflectivity is also wrong. There are no specs anywhere and I would be very surprised if they were any good in other respects. — Preceding unsigned comment added by 77.61.180.106 (talk) 13:52, 29 November 2021 (UTC)

@painted one: The site's author says he uses Color Place paint; I looked up some reviews online and that brand gets absolutely panned. I realise his cards are principally meant to be as cheap as possible so students can mess about with them and that they're not meant for professional or hobby use, but still... — Preceding unsigned comment added by 77.61.180.106 (talk) 14:40, 30 November 2021 (UTC)

Thanks

Thanks for all your feedback; I'll get on updating the page, and like I said, get on adding citations, I have some at home, but I'm not there till the end of the week.

C.anguschandler 01:27, 3 January 2007 (UTC)

Achromatic vs. flat spectrum

It's my sense that "gray card" implies achromatic under reasonable illuminants, but not necessarily flat spectrum. (Certainly good-quality gray cards are spectrally quite flat, and come with specifications.) Thus, I left out flat spectrum as part of the definition. Any photographer who understands color will agree with "if it's not achromatic under D65, A, etc., it's not a gray card", but the flat statement will probably meet with "hmm, that's maybe too strict". This is really an argument about established definitions, so we need a reference. Lexort 13:28, 21 January 2007 (UTC)Lexort

Here are some I just googled up: Robin Myers PDF, Michael S. Ross. You might want to say that flat is the ideal, and that they are usually pretty close to that. Dicklyon 17:44, 21 January 2007 (UTC)

white reflectivity

What is the range of reflectivity (reflectance) of ordinary white paper? What is the spectral curve, of ordinary white paper, and other ordinary white surfaces?-69.87.200.211 12:47, 15 May 2007 (UTC)

Depends on what you mean by "ordinary". Probably 80-90%, fairly spectrally flat. Problem is, however, that so much white paper is not ordinary, but rather contains fluorescent brighteners, which make for a much more complicated situation than just reflectance, and generally make the paper too blue to use for white-point calibration. Dicklyon 14:28, 15 May 2007 (UTC)

The paper industry has to deal with this issue because of metamerism. That's why they make a kind of paper called "true white." It may not be perfect, but it should at least not have the FWAs (fluorescent whitening agents), which are a type of OBA (optical brightening agent). True white is said to be better for printing photos on a computer printer because the appearance is more consistent under various lighting conditions. Zyxwv99 (talk) 13:48, 12 June 2014 (UTC)

A lot of paper nowadays does contain optical brighteners, substances that absorb UV and re-emit in the visible spectrum. It's possible to get paper that has an apparent reflectivity beyond 100%, e.g. WestRock produces paperboard with an apparent reflectivity of over 120% in outdoors conditions. Because optical brighteners emit blueish light, the base colour of the paper has to be yellowish to compensate, which creates the unfortunate side effect that papers like this may appear to change colour indoors, usually to a yellow or orangey tint. — Preceding unsigned comment added by 77.61.180.106 (talk) 10:58, 29 November 2021 (UTC)

Neutral under any illuminant?

I question this statement in the 2nd paragraph. If you illuminate a gray card with blue light only, it will reflect 18% of that blue light, so it will look blue, not gray. What this statement means by "neutral" is that it reflects light without changing its color, but it's misleading because the word "neutral" is used to mean "gray" in the rest of the article, and gray to most people means a broad spectrum of colors equally balanced. One could read this statement to imply a gray card somehow magically converts any wavelength of incoming light to a a flat spectrum of all wavelengths.

--Yes it would be blue in this situation, software can then be used to calculate what the correct temperature of a given image will be to compensate for the blue. — Preceding unsigned comment added by 87.194.93.168 (talk) 16:29, 16 July 2011 (UTC) mg (talk) 15:31, 5 February 2010 (UTC)

Chromatic adaptation will make the card appear neutral grey where the main light source is reasonably white, but there are limits to chromatic adaptation, think of stage lights for example, so the article is still wrong. I'll try to change the wording to something better.

History

The article should have at least some remarks on the history of grey cards, earliest use perhaps of improvised ones, earliest commercial grey cards, that sort of thing. — Preceding unsigned comment added by 77.61.180.106 (talk) 10:28, 29 November 2021 (UTC)

Image

What is the point of the image if the shade isn't quite right and it's just a rounded rectangle drawn in a drawing program? I feel that unless it's replaced by a calibrated photograph of a real grey card where the shade is exactly correct, e.g. #767676 if its spec says 18%, there really is no point. — Preceding unsigned comment added by 77.61.180.106 (talk) 14:53, 30 November 2021 (UTC)