Grey Cards .... erk!!!

[Ed Sukach]

Well, gang, as you may or may not know ., my very most favorite color paper - IlfoColor - has been discontinued, according to the Ilford web site. In its place, Ilford lists a "NEW!!!" color paper designed expressly for use in automated digital machinery, and is processed using RA-4 chemistry. Depending where one lands on the Ilford web site, this is either "suitable for use in conventional optical equipment" or, "NOT suitable for conventional optical equipment" (!?!?!?). Either statement appears to carry the same amount of weight ... so, being adventurous, and possibly not as sensible as I should be ... (possibly?) ... I'm going to give it a shot, when and IF I ever see it.

The situation is not much, if at all, better with Fuji papers. Same "suitable - not suitable" contradictions. A major trouble with Fuji is trying to delineate one paper from another. They have labelled their Crystal Archive paper in various ways, "Type C", "Type C5"; Type "C8"; Type "P" and "MP, and ... I have *no idea what the differences are. I'm wringing out Fuji "CDII" - go ahead, ask ... I will pre-answer: - No, I don't have foggy idea one about what it is - or is supposed to be - like.

Preliminary observations:

1. It is NOT Ilfocolor. The color balance is different. Not better or worse - but different.

2. It is about one stop faster.

3. It is a "grade" (if there was such a thing in color paper) or so "harder", and less forgiving of exposure variations.

More to come later.


NOW!!! The reason for the header above:

In wringing out the Fuji paper, I jury-rigged a target; a page from Ittens "Theory of Color", flanked by two (2) grey cards; one an older, KODAK and a newer "Delta - Last Grey Card You'll Ever Need".

Lo and behold... THEY ARE DIFFERENT!!! The Kodak card requires, on the average, 9cc less yellow color filtration (Omega DA5500), and one half to one stop more exposure to produce an area on the print that will have equal amounts of Cyan, magenta, yellow and the same density as that exposed to the Delta card!

Ha!! Not only that, but HAH!!!! I have always accepted a grey card as being "accurate" but this would indicate a lack of calibration to some grey standard. I have no idea which is correct.
I've always just grabbed a grey card - I have three or four of them - without giving them much thought. I'm THINKING now ... I'm thinking!! Where - has anyone seen a CALIBRATED grey card?

Additionally, I exposed a couple of frames with a "fair caucasian skin" target - my wife ... and I am certain that 9cc of color filtration DOES make a difference.

More to come later, as I wade through the assumptions I've made. Suffice it to say that I have one or two fewer today.

 

[Nick Zentena]

If you have one watch you know the time. If you have two you're never sure?

A grey card is supposed to reflect a certain amount of light I think. Does that really imply any colour? Could you make a grey card pink and have it reflect 18%? Don't know.

Plus don't they fade? I try to keep my card in the dark when not in use.

 

[chuck94022]

But do the cards produce the same black and white density? I always thought grey cards were calibrated for black and white exposure calculations, not for color correctness. I can certainly imagine lots of color combinations that would give you the same grey level when measured by a "color blind" light meter.

-chuck

[Edited: Nick, you beat me to the punch!]

 

[Ed Sukach]

Both cards were exposed together, in the studio, with Dynalite MX1000 packs and #2040 heads. I too, keep my cards in dark storage ... although not critically.

They are "grey". By definition Grey is equal parts of cyan, magenta, and yellow (a.k.a. "white") at a reflectivity of 18%. If the card reproduces as grey, by the same terms, the color balance should be somewhere near.

If a grey card DOESN'T reflect "18%", of what use would it be in black and white photography?

 

[Bruce Osgood]

Aren't all light meters color blind? I think so. They measure luminance and when measuring a gray card you expect them to read an 18%. You could have a Blue Card or Red Card as long as they reflected 18%, they would reflect middle gray.

 

[David Brown]

I can certainly imagine lots of color combinations that would give you the same grey level ...

I agree! My wife, a graphic artist/illustrator/painter, can seemingly differentiate more colors than we mere mortals even think exist. I've long since learned to stop saying anything was grey. She'll say "No, it's _________!" :confused:

Cheers

David

 

[Thomas Bertilsson]

My thinking is a grey card is primarily used for exposure. But if you think about it, in a color situation, it'll take fairly precise filtration to replicate the grey color of the gray card in a color print exactly.

Ed, it's an interesting observation, and I'll be watching this thread to satisfy my own curiosity.

- Thom

 

[Ed Sukach]

Exposure was not a factor. It HAD to be nearly equal on both sides of the frame, the shutter was only fired once. I was trying to determine difference between grey cards - or if there was any. There is!

Are exposure meters "color blind"? In a perfect world, they are... Are they in truth ...? Good question! I can't remember ever seeing a spectral sensitivity graph ... which proves nothing. The sophisticated cascade photometers we used (in a different life) were more or less color-blind, really measuring radiated energy ... but that has little to do with a run-of-the mill exposure meter.

Even if the response of the exposure meter is not chroma dependant, black and white film certainly IS -- see Fred Picker and his modified meters.

Hmm ... I need a tri-axis reflectance color spectrophotometer .. that will read "fair caucasian skin" as well as paper images. Think I'll find one on eBay?

In the meantime, it is "investigate and improvise" time.

 

[Lee L]

Ed,

As you're aware, not all meters have the same spectral sensitivity, as they have different sensor material. I'm no expert, but I understand that some are filtered back closer to even spectral response differently by different manufacturers, so an 18% blue won't meter the same as 18% green or 18% red across different meters. If you want that, you'll need a color meter. Seems that I read recently that Sekonic went for 15%, but I don't know how reliable that information was. But, as I understand it, the point is that a given color (especially a very saturated color) that reads as 18% reflectance on a selenium cell won't read the same as on a CdS cell, a gallium arsenide cell, or even another selenium cell meter made by another manufacturer. The closer to neutral (equal RGB reflectance) the standard 18% target is, the better.

Just as you are using them, the gray card is not only to meter from, but also to be used to filter for the same color in the final print. Theoretically, the filter pack that puts your Kodak gray card back at proper rendition will also put the Delta last gray card at the proper density and color balance, but no film/print material is perfect, so you just get acceptably close, depending on the materials and your preferences. (BTW, my properly stored Kodak gray cards have long outlasted the Delta Last Gray Cards I bought. The coating on the Deltas all went sticky and gooey and will now smudge and transfer to your fingers.)

There are other standards, like the Gretag Macbeth Color Checker and Kodak color separation guides, that have a gray scale and some standard color swatches to check color replication. (I can't mention here that my computer imaging program, Picture Window, will take a scanned shot of a Macbeth color checker or the gray scale in a Kodak Q-13, align to the swatches, and then massage the numbers to correct color balance and density.) I've found the Macbeth very useful for determining filtration for color transparency films and for color correcting prints in the darkroom.

Lee

 

[Ed Sukach]

This is a *crappy* scan of the makeshift target. Exposure was determined with a Gossen Ultra-Pro meter in "flash" mode, with Studio attachment.

 

[mark]

That is one nice lookin grey card you got there. Did you pick that up at a normal photo store or was it special order

 

[L Gebhardt]

Sticking a Kodak card in the desitometer gives the following readings:

Red .65
Green .66
Blue .70

Maybe this will help.

 

[Eric Rose]

IMHO grey cards should not be used to determine color balance when printing. As you have found they vary quite a bit. Even if you used the same one each time, the chore of trying to get a good color match would be a frustration not worth the effort. I use the Kodak color seperation and step wedge thingies as well as a white sheet of paper all in the frame together. The combination gives me all the information I need. Oh ya and a good south facing window for light during evaluation. That's my method YMMV.

 

[Lee L]

Ed,

I wouldn't go for making the gray card read neutral gray on the print as measured by a densitometer, i.e. for equal RGB reflectances, I'd work at making the print look visually like the gray card you shot. This is usually judged under high color rendition index lights, GE Chroma 50 flourescent lamps or similar. You could also go for the lighting in which the print will be displayed, but that gets trickier. More colors on the target, like the Kodak Q-13 or the Gretag Macbeth Color Checker, actually make color balancing easier to do.

As for 9CC being significant in printing, in studios I used to work to less than a maximum of 2.5CC units for commercial ad work, where color wasn't all that critical. For other, more critical uses, I'd work to tighter tolerances. (This on 4x5 transparency films.) I do the same when printing.

BTW, as I'm sure you noticed, there are significant differences in color within each gray card on your scan. The film doesn't look like that, does it?

Lee

Lo and behold... THEY ARE DIFFERENT!!! The Kodak card requires, on the average, 9cc less yellow color filtration (Omega DA5500), and one half to one stop more exposure to produce an area on the print that will have equal amounts of Cyan, magenta, yellow and the same density as that exposed to the Delta card!

Ha!! Not only that, but HAH!!!! I have always accepted a grey card as being "accurate" but this would indicate a lack of calibration to some grey standard. I have no idea which is correct.
I've always just grabbed a grey card - I have three or four of them - without giving them much thought. I'm THINKING now ... I'm thinking!! Where - has anyone seen a CALIBRATED grey card?

Additionally, I exposed a couple of frames with a "fair caucasian skin" target - my wife ... and I am certain that 9cc of color filtration DOES make a difference.

More to come later, as I wade through the assumptions I've made. Suffice it to say that I have one or two fewer today.

 

[Ed Sukach]

BTW, as I'm sure you noticed, there are significant differences in color within each gray card on your scan. The film doesn't look like that, does it?
Lee

No, the film doesn't look like that - it is negative film. By eye, yes, the card color does look significantly different - supported by the analysis.

The density difference is not that pronounced, either ... I think that is due to the characteristics of the Fuji Crystal Archive paper.

 

[Kirk Keyes]

The first thing I would do is get even lighting on your targets- you don't appear to have that now. The lower right looks obviously darker than the upper left. This could be a very big issue - you are just making things harder by trying to match grays from areas of different negative densities. Ed said, "Exposure was not a factor," but the print indicates this may be otherwise.

Ed wrote, "Where - has anyone seen a CALIBRATED grey card?"

Yes - and you have too! The easiest one to find is the Macbeth Color Checker chart. It uses specially formulated paints to make all the targets on it. I've got a paper that was written when the Color Checker came out in the mid-70s, and the grey steps are very neutral from 450 to 700 nanometers, below 450nm, they start to drop in reflectance as the wavelength gets lower.

Have you measured your two cards with a densitometer to see if they really are close to neutral? Or evne close to each other?

Also, you said one card was printed in a book - the printing inks may not be very neutral. That is one reason that the Macbeth uses paints.

Chuck wrote, "I always thought grey cards were calibrated for black and white exposure calculations, not for color correctness."

The Macbeth is designed for color correctness.

Ed wrote, "By definition Grey is equal parts of cyan, magenta, and yellow (a.k.a. "white") at a reflectivity of 18%."

Ed, this is not really right. You would be closer to the truth is you have written "By definition, Grey is equal parts of red, green, and blue at a reflectivity of 18%." Your camera is measuring the light from the grey card, not printing inks or dyes.

It's possible to make fairly pure colors of RGB for making an exposure, but the problems will start when you start using colors like Cyan, magenta, and yellow when printing. Cyan is a mixture of green and blue, and magenta is a mix of red and blue, and they are often not (chromatically) pure mixtures.

When color printing, some of the red, green, and blue reflectivities that make up an image are contaminated by colors from each of the dye layers in the print (and the film as well).

For example, when making meaurements of a supposedly pure blue patch on a print, there will be some wanted blue density from the magenta dye layer, some blue density from the cyan layer, and some unwanted blue from the yellow dye layer. But since each of those layers contain other colors, that blue patch will also have some red from the magenta layer, some green from the cyan layer, and some yellow from the yellow layer. That blue patch will not be a pure blue. The same thing will happen when you try to print a neutral grey - there should be equal amounts of RGB, but there will be unwanted amounts of the "impurities" found in each of the dye layers that made up that grey patch. You should get ahold of Photographic Sensitometry, by Zakia and Todd for much more thorough discussion on this complicated issue.

Ed wrote, "Even if the response of the exposure meter is not chroma dependant, black and white film certainly IS -- see Fred Picker and his modified meters."

Meter response most certainly is color dependant. But that should not be an issue here.

Lee has made some good points on the subject of the light used to make visual color balance observations.

Kirk - www.keyesphoto.com

 

[Helen B]

Ed,

As already mentioned, the Kodak Gray Card may not be a truly neutral grey, just as the white side may not be a truly neutral white. I've found that the 'Gray Card Plus' is a little more accurate - as well as being more useful - but I do change it regularly, and don't use it for critical work.

There are calibrated charts - but at a calibrated price. I use DSC charts. These come with a calibration certificate, and a recommendation to renew them regularly (you can trade your old one in!). They are primarily intended for setting up video cameras, but they are equally useful, if a bit OTT, for film. There is now a swimsuit edition as well as the plain greyscale version, by the way.

Dead Link Removed is an article on grey card neutrality. The author has an interest in promoting his grey card, but the information seems good, if restricted in which cards were measured and the number of samples.

Best,
Helen

 

[Ed Sukach]

Thanks, Helen!! Many!

I'll look into this more thoroughly tomorrow.

 

[Ed Sukach]

Helen, and others interested ...

The quest for a suitable grey card continues.

The DSC web site contains a wealth of information -- bordering on plethora. Apparently "good" products, but kind of intimidating.
The article enclosed there, written with information about the Gretag/ MacBeth Color Checker and its problems with UV illumination was "very* informative. For the price, one would expect better performance.
I wish there was more direct information of what to choose for a simple, run-of-the-mill configuration, and calibrated grey card - and at least some indication of prices. I do like their construction - using an aluminum substrate, and a clear plastic overcoat.
There is an offer - a "special" where one could save $290 .... what would the original price be to allow such a saving?
Which DSC card do you use, and could you suggest a dealer?

Now, I've searched through the "usual suspects" ... er ... dealers. No one seems to stock the most promising candidate so far ... the Kodak "Grey Card Plus", catalog #847-8174. I'll e-mail one of our sponsors, Calumet, and see if it can be obtained.
Speaking of Calumet - there is an indication of the problems one might encounter in a search like this: They list a "Robin Meyers Imaging Digital Grey Card." Seems pretty good at first glance ... in 10 x 15 cm size. The next listing .. apparently the same card in a different size - 15 x 22.5 cm, carries a warning label: The Digital Grey Card is designed for digital photographers only. It will not work with film light meters". I thought grey would be grey, would be grey...?

All that as it may be, the only indication I've been able to see about accuracy is a claim by Delta, for a very inexpensive version of their grey card - "Accurate to 1%".

This all will all be useful in my future work. Now, I will be working to find "correction factors" for use with one of my existing Delta grey cards ... I am going to shred the Kodak card I have ... apparently - and for whatever reason - it is `WAY off. Although the prints I have of my latest work are certainly OK, I'll be making a LOT of test exposures with various color balancing to determining "correction factors" - by trial and error.
I'm pressing my wife and daughter into service. Both have far better color vision than I do.

Once I get all this sorted out, I'll be concentrating on what happens with this HP scanner I've been using....

On to the darkroom.

 

[Lee L]

Ed,

In looking around a bit more, I found a couple of German products I hadn't seen before, and which are more affordable than the DSC options. (BTW, the way I read the DSC special pricing, it was "buy one, get one free", so you'd be spending at least $290 to get two cards.)

The Fotowand grey card and color grey cards are more reasonable in price, are on a washable plastic substrate, come in a couple of sizes, and the "color" version has circles with 5CC each of R, G, B, Y, M, and C, plus two patches of darker and lighter grey. This might help with judging subtle color shifts. Their US dealer catalog page is at: http://www.thedopshop.com/cat-charts.cfm?catid=62 They also have some gray scale and color patch cards.

I haven't use the Fotowand products, so can't vouch for them personally. They do look interesting, though. The manufacturer's page is: http://www.fotowand.com/cv.htm?/dual.htm#4985eng.htm

Differences in the ability to perceive color are common, and if I recall my reading correctly, women are generally better at it than men. When I was working in commercial studios, I was often "borrowed" by studios near the ones I was working in, to make close calls on color balance clip tests by people who wanted a second opinion or didn't trust their own judgement.

I, too, am curious about that "digital" gray card, and the claim that it won't work for film cameras. I spoke with Calumet yesterday about a gray microfiber cleaning cloth they carry, but they couldn't tell me if it was the Wico 18% gray. I've wondered why I hadn't seen that product in the market.

Lee

 

[tim atherton]

Aren't all light meters color blind? I think so. They measure luminance and when measuring a gray card you expect them to read an 18%. You could have a Blue Card or Red Card as long as they reflected 18%, they would reflect middle gray.

And I seem to recall many meters are calibrated for what is it - 13% grey anyway.

 

[Stephen Benskin]

Meters are actually calibrated to a luminance and not a reflectance. The value of the lumininant is 297 footlamberts. The meter will calculate the scene with the f/stop so that 8 mcs at one second are hitting the film. The exact exposure is determined by 8 x shutter speed. For a 125 speed film, the midtone (calibrated) exposure is 0.064 mcs. If anyone wonders, simply put, this how the Sunny 16 rule works.

If you are wanting an equivalent reflectance, it is 12% when compared to an incident meter using the hemisphere and 16% when using the flat surface on the incident meter.

 

[Kirk Keyes]

Here's some data on the Macbeth Color Checker Chart - an excel spreadsheet that lists the spectral reflectance factor of each patch on the chart broken down by wavelength (5 nm steps, too!).

http://www.cis.rit.edu/mcsl/online/CIE/MacbethColorChecker.xls

kirk - www.keyesphoto.com

 

[Kirk Keyes]

I made a graph of the spectral data for the Macbeth Color Checker Chart - here's a link to it:

http://www.keyesphoto.com/KdktechMacbethGraph.html

Kirk - www.keyesphoto.com

 

[Ed Sukach]

Another chapter in the continuing saga of The Grey Card Caper ..

After careful processing and Wife-supplied "Fair Caucasian Skin" evaluation, I've set up a ColorStar Channel for use in analyzing my figure study work in the enlarger. The "correction factors" I've been able to establish (- probably of NO help to anyone else) are: Cyan, 00; Magenta, +03; Yellow, +09. These will be added to the Dichro settings from the analyses of the grey card image usually taken in the first frame of my work. These only apply to images taken with Agfacolor 400, developed in Tetenal, and printed on Fuji Crystal Archive CDII, with an - MY - Omega D5500 enlarger.
Next is the same exercise with my existing stock of Ilfocolor paper.

The weak link here is the subjective evaluation of "Fair Caucasian Skin" - and I know of no way to make that objective, short of taking Reflected Color Spectrometry readings of the model herself.

Oh, by the way ... I've been posting using "subtractive" terms, Magenta, Cyan, Yellow and (should be 'K") Density.... because that is what I am working with at the moment. I just happened to think, though ... It isn't possible to have an "additive" grey. There is no, nor can there be, a "grey light", only different strengths of white light.

I've e-mailed Calumet, requesting information about the Kodak Grey Card Plus, Kodak Cat.# 847-8174, per Helen B.s recommendation.

There is a whole lot of processing going on. I am nothing if not tenacious, though. Black and White is beginning to look more appealing, though.