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Gray card proper usage

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Dene

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Hello again. Thanks for all the previous help and here we go again.

I just purchased an 18% gray card. When I initiate Lightroom and go to the WB picker, I can pick several different spots on the card and get very different readings. They all make the WB of the shot look acceptable, but should this be? Should I walk close and or zoom into the card to fill frame or get the subject to hold it at a more precise angle angle?



--
Thanks from Dene in Canada
 
Dene said:
Hello again. Thanks for all the previous help and here we go again.
I just purchased an 18% gray card. When I initiate Lightroom and go
to the WB picker, I can pick several different spots on the card and
get very different readings. They all make the WB of the shot look
acceptable, but should this be?
Click to expand...
Yes. All colored objects in front of the gray card (and outside the frame of the picture) are reflecting colored light, which is striking the gray card willy-nilly and slightly altering is neutrality. The keyword is "slightly." Run your eyedropper (3x3 sample) over the gray card you posted and watch the RGB values on the Info palette. They vary all over the place -- but not by much. I would just click with the WB tool and stop on the result that looked best to me.
Dene said:
Should I walk close and or zoom into
the card to fill frame or get the subject to hold it at a more
precise angle angle?
Click to expand...
No. See above. If you move closer, any colored clothing of objects on you are likely to cast a stronger reflection on the card, further altering its neutrality. Zooming in won't matter because it won't diminish colored light reflected from other objects around the gray card. It will only make the gray card fill more of the frame.

--
~ Peano
http://www.radiantpics.com
 
DigitalDetailer said:
To use a gray card the right way it must fill the whole (or at least
better part of) the frame.
Click to expand...
Really? I clearly need to do a little more reading on this, then. I just purchased a WhiBal card and it was my understanding that I only needed the subject to hold it up (with no glare) for one shot and then I could set all the following shots from that in Lightroom. Unless I completely got it wrong, I thought I did NOT have to fill the frame. Just have the subject hold it up.

Elise
 
An 18% Gray Card is for metering light. It is not the same as the Graybalance Card by Whibal.

Mike
http://www.mikedubu.com
 
That's a very valid point. The ISO was 100, but despite what everyone thinks, my 40D exhibits noise in even the very minimal shadow areas of outdoor pictures. Off topic, I took 75 pictures in bright sunlight of a baseball game and the players uniforms came out clear and crisp but their faces under the ball caps were molten wax like. Horrendous! ISO100 I say!
Thanks
 
Without checking the Info palette, I laid down these two sample points and predicted (to myself) that #1 would have a higher red value. Sure enough, thar she blows. Why so? Because skin tones are predominantly red. That finger is reflecting a red hue onto the gray card and altering its neutrality.

Your best bet is to keep the gray card our of close proximity with colored objects. Where there's skin involved, as here, just sample the card away from that distorting object. The RGB values at point #2 -- 131.129.130 -- a close enough to neutral for government work.



--
~ Peano
http://www.radiantpics.com
 
Dene said:
Thanks Mike. What it says on the wrapper is it is a Gray Card. I
didn't know there were different types for exposure and WB etc.
--
Thanks from Dene in Canada
Click to expand...
The Kodak Gray Card is for taking a light reading. The Whibal and Gretag Macbeth Gray cards or Color Checkers can be used for what you are trying to do which is use the eyedroppers on the chart in the image to color balance your image based on the white, black and gray. The mini color checker works pretty well for close work and fits in your pocket.

All this stuff costs a fortune. :) I also use the ExpoDisc, which is easy to carry around. Get the biggest one and just hold it in front of your lens. Don't try to buy one for every size lens you have.

Mike
http://www.mikedubu.com
 
slightly off topic but surely you can purchase some card at a stationary shop that would come close to a gray card. Anyone have any experience using anything other than from photography suppliers !!!!
 
There appears to be some confusion here. First, 18% grey cards are used for setting exposure and WhiBal cards are for setting white balance. 18% grey cards are an artifact from film photography days and are less useful with the advent of digital cameras using reflected light meters; they also shouldn't be used for white balancing because generally they are not spectrally neutral. For setting exposure, learn to trust the various metering modes in your camera (change them according to the lighting situation) and read the histogram. Or for really accurate exposures use an incident light meter (less useful if the subject is inaccessible).

Second, there are at least two ways to use a WhiBal card. Filling the frame is preferred when using the WhiBal to create a Custom White Balance setting in-camera. For reference shots, as you mentioned, placing the WhiBal card in the scene is sufficient. You get the best color accuracy when using both a Custom White Balance setting and a reference shot of the lighting conditions.
Snowsilver said:
DigitalDetailer said:
To use a gray card the right way it must fill the whole (or at least
better part of) the frame.
Click to expand...
Really? I clearly need to do a little more reading on this, then. I
just purchased a WhiBal card and it was my understanding that I only
needed the subject to hold it up (with no glare) for one shot and
then I could set all the following shots from that in Lightroom.
Unless I completely got it wrong, I thought I did NOT have to fill
the frame. Just have the subject hold it up.

Elise
Click to expand...
 
I'm impressed by the number of times you manage to be wrong in one pargraph! Here is the Wikipedia entry on gray cards:
http://en.wikipedia.org/wiki/Gray_card
suddie1215 said:
There appears to be some confusion here. First, 18% grey cards are
used for setting exposure and WhiBal cards are for setting white
balance. 18% grey cards are an artifact from film photography days
and are less useful with the advent of digital cameras using
reflected light meters; they also shouldn't be used for white
balancing because generally they are not spectrally neutral. For
setting exposure, learn to trust the various metering modes in your
camera (change them according to the lighting situation) and read the
histogram. Or for really accurate exposures use an incident light
meter (less useful if the subject is inaccessible).
Click to expand...
 
Well if you want to rely on Wikipedia entries for accurate information on photography, more power to you. No doubt you missed that I was comparing traditional grey cards to a WhilBal. Not all grey cards are 18% and cards - especially those made from cardboard - lose their accuracy over time. By comparison WhiBal is made from material that does not deteriorate and is guaranteed by the manufacturer to be spectrally neutral.

I have no problems being proven wrong; but what you posted does not rise to the level of proof. Perhaps my use of qualifiers like "less" and "generally" confused you.
 
to one degree or another! I have both, a gray card as well as a digital gray card for balancing color, but many times I only use the 18% gray card to do both! You can get better results with a gray card than you get with no card, you also can use the gray card for both purposes and while the digital gray cards or WB cards do a great jog balancing colors, they can not be used to check exposure. It is great to have all this tools when shooting in the studio, but I'm not sure if anyone would really use both cards when shooting outdoors.
--
Alfred
 
Totoro111 said:
suddie1215 said:
There appears to be some confusion here. First, 18% grey cards are
used for setting exposure and WhiBal cards are for setting white
balance. 18% grey cards are an artifact from film photography days
and are less useful with the advent of digital cameras using
reflected light meters; they also shouldn't be used for white
balancing because generally they are not spectrally neutral. For
setting exposure, learn to trust the various metering modes in your
camera (change them according to the lighting situation) and read the
histogram. Or for really accurate exposures use an incident light
meter (less useful if the subject is inaccessible).
Click to expand...
Click to expand...
Totor the only person that is wrong here is YOU.
Snook
--
1DsMII,5D,G5 D2.0---> Shooting RAW (Ofcourse)
http://homepage.mac.com/ekphotography/2006
http://homepage.mac.com/ekphotography/F30/
http://homepage.mac.com/ekphotography/Leica
 
Suddie, your comments about photographic gray cards and reflected light metering in digital v. film cameras were generally incorrect.

It is not a question of Wikipedia v. other references. A quick reading of virtually any reference on using photographic gray cards, proper exposure, reflected light metering, and white balance will provide exactly the same information as the Wikipedia entry.

It is no defense to say you were referring to some gray cards. I am unaware of any photographic gray card that does not have a flat reflectance spectrum. Please name the manufacturer, if you are familiar with one. Of course, using gray construction paper or something like that is not the equivalent of a photographic gray card. ;) It was obvious that the OP was talking about using a photographic gray card.

Digital SLRs and film SLRs use reflected light meters. Even spot metering is reflected light metering. I am not aware of any digital SLR with incident light metering.

It is true that modern SLRs, digital and film, have better metering. They use arrays of metering sensors for differing patterns of average and/or center-eighted metering, and they are harder to fool that metering in cameras from a decade or more ago. That does not make a photographic gray card irrelevant. You can get better exposures with them. The downside is that they slow you down.

Digital SLRs can indeed use a gray card for white balance. A gray card is better for white balance than a photographic white card because it is less likely to clip in bright light.

The likely reason that the OP sees different values for the gray card is uneven illumination. The gray card was likely not perfectly parallel to the lens.

For white balance, the best approach is to fill the frame with the gray card. Most digital SLRs these days include a custom WB function that calls for a photographic gray card.

To even out the illumination with a shot like that from the OP, make a temporary layer duplicating the pixels. Apply a slight gaussian blur. Then calculate your white balance from the gray care and delete the temporary layer.

Cheers,

Mitch

--
http://www.thelightsrightstudio.com
http://www.thelightsright.com
http://groups.yahoo.com/group/TheLightsRight/
http://www.thelightsrightstudio.com/SharpeningYourPhotographs.html
 
gmitchel said:
Suddie, your comments about photographic gray cards and reflected
light metering in digital v. film cameras were generally incorrect.
Click to expand...
Suddie's statements are correct. The Kodak 18% Gray Card is not Spectrally Neutral. It was intended for taking exposure readings, not setting white balance after the fact in digital processing. The Whibal Graycard is Spectrally Neutral and is intended for setting white balance in your camera or setting white balance after the fact during digital processing (using the middle eyedropper in curves to set white balance). Kodak is coming out with a Digital Gray Card soon. If you don't agree with Whibal's and Kodak's technical claims, saying it doesn't matter if you use a Spectrally Neutral Gray Card for setting white balance, then that is your personal opinion.

Mike
 
Glenn, I really appreciate and respect your vast photographic knowledge. However, you are ascribing words/thoughts to me that I never expressed. The least you could do is read what I actually wrote rather than what you THINK I wrote. For example, I NEVER said anything about digital cameras using incident light meters.

Mike, thanks for your input and clarification.
gmitchel said:
Suddie, your comments about photographic gray cards and reflected
light metering in digital v. film cameras were generally incorrect.

It is not a question of Wikipedia v. other references. A quick
reading of virtually any reference on using photographic gray cards,
proper exposure, reflected light metering, and white balance will
provide exactly the same information as the Wikipedia entry.

It is no defense to say you were referring to some gray cards. I am
unaware of any photographic gray card that does not have a flat
reflectance spectrum. Please name the manufacturer, if you are
familiar with one. Of course, using gray construction paper or
something like that is not the equivalent of a photographic gray
card. ;) It was obvious that the OP was talking about using a
photographic gray card.

Digital SLRs and film SLRs use reflected light meters. Even spot
metering is reflected light metering. I am not aware of any digital
SLR with incident light metering.

It is true that modern SLRs, digital and film, have better metering.
They use arrays of metering sensors for differing patterns of average
and/or center-eighted metering, and they are harder to fool that
metering in cameras from a decade or more ago. That does not make a
photographic gray card irrelevant. You can get better exposures with
them. The downside is that they slow you down.

Digital SLRs can indeed use a gray card for white balance. A gray
card is better for white balance than a photographic white card
because it is less likely to clip in bright light.

The likely reason that the OP sees different values for the gray card
is uneven illumination. The gray card was likely not perfectly
parallel to the lens.

For white balance, the best approach is to fill the frame with the
gray card. Most digital SLRs these days include a custom WB function
that calls for a photographic gray card.

To even out the illumination with a shot like that from the OP, make
a temporary layer duplicating the pixels. Apply a slight gaussian
blur. Then calculate your white balance from the gray care and delete
the temporary layer.

Cheers,

Mitch

--
http://www.thelightsrightstudio.com
http://www.thelightsright.com
http://groups.yahoo.com/group/TheLightsRight/
http://www.thelightsrightstudio.com/SharpeningYourPhotographs.html
Click to expand...
 
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