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# Thread: Grey Cards .... erk!!!

1. Originally Posted by Bruce (Camclicker)
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.

2. 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.

3. 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/C...lorChecker.xls

kirk - www.keyesphoto.com

4. 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

5. 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.

6. Originally Posted by Ed Sukach
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.
While we don't usually think of different levels of illumination as being different shades of grey, I think that if you talked to some people that are really experienced in lighting (i.e. theatrical or motion picture grips), they would tell you otherwise.

And when you are sitting in front of your computer, you are dealing with additive grey all the time. Your computer uses the additive RGB system for displaying colors, and any time you have equal amounts of RGB, you have shades of grey. RGB = 200,200,200 or 128,128,128 or 15,15,15 - they are all grey.

Earlier, I mentioned that there was a system that color sensitometrists use for calculating impurities in color printing systems, and I could not remember the name of it - it's called the "END" system - Equivalent Neutral Density. All color dyes in film (and paper) had a wavelength region of maximum density, but then they also have some absorption at all wavelengths, a secondary density, and this is where the problems come in. The END system allows one to make measurements of both of these regions, and to make corrections for the secondary density of the dyes. But it does require a reflection densitometer in order to use this system when printing. And for general printing, unless you have a grey target, it will probably not help. (But understanding the theory behind it may be good!)

Instead of a regular grey card, I would suggest that you get the one here: http://www.thedopshop.com/item.cfm?itemID=213 that Lee pointed you to. I think that having the RGBMYC ring-around patches at +5CC density would be a great assistance for what you are doing.

Kirk - www.keyesphoto.com

7. I emailed the DoP Shop about the Fotowand Color Grey Card mentioned by Kirk in the last posting to ask about specifics. The lighter and darker patches of neutral grey are +/- 1/3 stop from 18% reflectance. So placing exposures at 1 stop intervals using the card will give you spots to read at 1/3 stop intervals through whatever total range in f-stops you decide to use.

Lee

8. I've been trying to buy a Kodak Grey Card Plus, Kodak Cat. #847-8174. It hasn't been easy. I've e-mailed our sponsor, Calumet, three times, as to availability/ orderability from Kodak, and have received NO answers.

Sometimes, I moonlight as a Legal Courier - last Monday I had to deliver a package to the Suffolk Superior Court in Cambridge, MA, a stone's throw away from Calumet in Cambridge.
So I visited - up front and personal. Disappointing. I talked to a counter clerk who, rather obviously, was not into film-based photography. He kept muttering about how their "stock" grey cards were effective for D****** work... how one had a panel very useful in achieving a "white balance". When I remarked that neither my Hasselblad 503Cx, nor my Dichroic Head on my enlarger had any provisions for "white balance" it resulted in a CLASSIC "deer-in-headlights" reaction.

Anyway - I started to post a method for dealing with scanner color balance ... and I sidetracked myself into this rant. See next message.

9. Eureka! EUREKA!!! Where is that Hecatomb....

Sitting here, typing away, and scanning for submission to APUG - I had an inspiration. As everyo .... MANY know, there has been a LOT of discussion about "color fidelity" and how to achieve it.
I was thinking about the fact that I do not yet have a CALIBRATED grey card, when the thought occurred to me... True, but I DO have the original grey card, and a photographed and printed image of it (see Technical Gallery). Not only that, but the original grey card would fit on my scanners glass. So, I scanned the grey card itself. Using the program that came with the H-P Scanner, I analyzed that image. That program will not give values in the usual sense - Red, Green, Blue - but will indicate values derived from Cartesian coordinates*, based on a color "wheel".

The Delta grey card I used analyzed out to: X +4; Y + 1.
The Printed image of that grey card: X +13; Y -3.

So, If I scan another photographic image (the color balance does not materially change from frame to frame, unless there is a change in the lighting - I know that from a lot of enlarging work with the ColorStar), and apply that "fudge factor"; the differences of those two analyses: X -9, Y +4, - I am going to be pretty darn close.

Now, I am going to post images here, with a reasonable level of certainty, that they are correctly "color balanced."

* Does that "date" me? Anyone else remember "abscissa" and "ordinate"?

10. Ed,
Calumet has always been pretty slow with my E-mails but their 1-800 # is free and the folks on that end do know what you are talking about. I also never trust the guy behind the counter. I want someone who can type a number into their computer and give me the real answer not a salesman who may or may not have a clue what I want.

I realize why you want color balance in your scans but as you said before it looks right to you in real life. Who cares what a scanner has to say since we know it detracts from the quality of the final image anyway. Most folks here know that and take it into consideration. If someone wants to piss and moan about your color balance from a scanned print on a monitor, let them. I personally have not noticed your posts having odd color.

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