Is it Gray or Grey?

[rolandogomez]

Just a fun poll to see how folks act, but in photography, depending how you say it, gray, or grey, is very important, especially at 18%. Can you tell me why? Yep, this is a test for the next 60-seconds.... thanks, rg sends!

[PhotosbyChuck]

Most cameras' reflective metering will give an accurate reading of exposure on an 18% gray surface. That's exposure ... not color balance. However, many people do use 18% gray cards as a way to set white balance -- often with disappointing results since the cards were a way to precisely meter density, not color.

[r_fredrick_smith]

Originally Posted by rolandogomez

Just a fun poll to see how folks act, but in photography, depending how you say it, gray, or grey, is very important, especially at 18%. Can you tell me why? Yep, this is a test for the next 60-seconds.... thanks, rg sends!

Shades of gray!

Here is the link to the long discussion that we had on this subject on G1 which covered a lot of ground:

What is gray? - Glamour 1™ Putting the Glamour Back in Photography!

Cheers,
rfs

[r_fredrick_smith]

Originally Posted by PhotosbyChuck

Most cameras' reflective metering will give an accurate reading of exposure on an 18% gray surface. That's exposure ... not color balance. However, many people do use 18% gray cards as a way to set white balance -- often with disappointing results since the cards were a way to precisely meter density, not color.

As long as the card you use is really gray, or actually any neutral color (having equal parts of r, g and b) then it will work just fine for CWB (Custom White Balance). Here are a couple of demo shots to show this. Both images are of a Macbeth card. I used a gray card (Photovisiion Calibration target (middle stripe)) to set the CWB and then took the shot of the Macbeth. On the second shot, exact same thing, except I used the white stripe to set the CWB. As you note the two Macbeth cards are almost identical.

Keep in mind I used the target shown below to create the reference shot that was used to set CWB for each of the above. I just made sure that in one the gray part was in the center area and for the other the white part was in the center area (Canon 20D uses just center area for CWB).

And here is what the target looked like

Cheers,
rfs

[PhotosbyChuck]

You're right in that any neutral surface can be used to CWB. But the assumption that a "true" 18% gray is neutral isn't right. 18% gray is a measure of the reflective quality of the gray...not the balance. So, the problem is that not all 18% grays have the same color balance. The same is true for whites. Not all whites are equally balanced.

Good news is, if you stick with a card you can balance to that card ... but that may not work for another brand.

[r_fredrick_smith]

Originally Posted by PhotosbyChuck

You're right in that any neutral surface can be used to CWB. But the assumption that a "true" 18% gray is neutral isn't right. 18% gray is a measure of the reflective quality of the gray...not the balance. So, the problem is that not all 18% grays have the same color balance. The same is true for whites. Not all whites are equally balanced.

Good news is, if you stick with a card you can balance to that card ... but that may not work for another brand.

I'm not sure what your point is. If you buy a quality gray card, then it is going to be neutral and hence suitable for CWB. It will also be suitable for use in determining exposure by using it in combination with the camera's histogram. If you shoot the gray card full frame, then you will get one spike somewhere in the histogram. If it is right in the middle, then that is telling you that the card is registering as 18% gray (depending on which theory you follow). Now if it is not in the center, you can shoot the target again after adjusting exposure and see where the spike ends up, always trying to move it to the middle. At that point you know the best exposure for middle gray. But depending to the predominate colors in the scene, you may now need to shift that exposure up or down to compensate for the reflectivity of the colors you are interested in. This is sort of like a modified zone system.

18% gray is more like a shorthand statement that has little meaning outside its generally understood shorthand meaning. Some people even choose to talk about 13% gray instead.

But when we talk about gray cards, we are really only interested in that gray card being neutral. The classic gray card is in the middle of the white black range (128 r, 128 b, 128 g).

Bottom line: if you use a known gray card for CWB, you will get accurate results equal to those gotten with a known white card.

Cheers,
rfs

[PhotosbyChuck]

The point is that reflectance and color balance are two different things. It's possible for a warm grey and a cool grey to both reflect the same amount of light and therefore give the same exposure settings, but result in different colors.

Your own Macbeth shots show color variation between the two methods. In your top/bottom layout, it's not as easy to see as in this shot, where I overlayed them and deleted strips from each row to reveal the other card. Colors with high red values are the closest match. Others are fairly far off such as the brown in the upper left corner. Even the grays are different. Look at the bottom row, third square from the left and tell me that's the same color balance...



They're close. And if your point is that "close enough" is fine for most work, I'd certainly agree. But I stand by the original observation that 18% gray is about exposure.

[r_fredrick_smith]

The only difference I can see in your example is difference is brightness. One is brighter than the other. Since I did not do my two original example shots in a laboratory we would expect some small variation like that. It does not change the fact that anyone using a good gray card for their CWB reference shot will get good color balance that is highly usable. We all tend to play with the CB a bit after the fact anyway to warm things up or even sometimes shoot warmer. So I sometimes take by CWB reference using warm card and the CWB now gives a slightly warmer result. And as far as I can tell, I really never said anything about reflectance and CWB as far as I can recall.

But on another note, when I tested the Expodisc I found that I got almost identical CWB settings as when using the gray card. So that should suggest that reflectance is not the real issue (in most cases) --- the Expodisc does not depend on reflectance from a card (as you know).

So to be honest, I'm still not sure I understand what point you're making. When I look at what you said here:

The point is that reflectance and color balance are two different things. It's possible for a warm grey and a cool grey to both reflect the same amount of light and therefore give the same exposure settings, but result in different colors.

The first sentence doesn't seem to refer to anything that I said. From the way I read your statement your are talking about several different gray cards. I've never heard of a warm or cool gray card. You can have a warm card that is a shade of cyan, or blue or green and you can use these to get different results that could take middle gray as a starting point. All gray cards (if they are really gray cards) are by definition neither warm or cool --- they are neutral (equal values of RGB). So do you see where my confusion over your remarks stems? Are you saying something else, and I'm just missing it.

Of course, in the real world, for 99% of the photos, all that one really needs in regards to white balance is consistency. If you have a known reference in a lighting set (such as a photo of a w/g/b target), then you can have any color balance you want (and RAW makes this even easier). But I still like to use CWB, because I like the embedded JPG in the RAW file to already be close to proper WB and I like to be able to use the LCD image for various purposes and since it is using the current WB setting, then I want to be in the ball park there.

Cheers,
rfs

[PhotosbyChuck]

Originally Posted by r_fredrick_smith

The only difference I can see in your example is difference is brightness.

Then you're missing the fact that the outer bands have significantly (roughly 5%) more red in them than the inner bands. Sample your own RAWs processed with the same color temps to be sure. All I had were the JPGs you posted.

Originally Posted by r_fredrick_smith

It does not change the fact that anyone using a good gray card for their CWB reference shot will get good color balance that is highly usable.

I said as much above. We don't disagree. "Good" is relative. Is a +/- 5% variance in red and a +/- 3% variance in green good? For most things.

Originally Posted by r_fredrick_smith

I really never said anything about reflectance and CWB as far as I can recall.

Originally Posted by r_fredrick_smith

But on another note, when I tested the Expodisc I found that I got almost identical CWB settings as when using the gray card. So that should suggest that reflectance is not the real issue (in most cases) --- the Expodisc does not depend on reflectance from a card (as you know).

Ah...I see part of why you're not following the reflectance comment. I just mean the light bouncing off of the card to be metered by the camera. It's called 18% because 18% of the visible light hitting the target is reflected. Back in the film days, someone figured out that 18% reflectance was the midpoint between white and black. To get the most of the film's lattitude, exposure could be set to a surface with a neutral 18% reflectance.

Ever use grass for this..it works pretty darn well for exposure -- about as well as a grey card. Just don't try it for CWB! So for the card to be "18%" it has a reflectance value of 18%. For it to be grey, the light across the spectrum must be reflected at exactly the same 18% without any variance. This is what I mean when I say that the card's reflectance value is for exposure settings rather than color balance.

Originally Posted by r_fredrick_smith

So to be honest, I'm still not sure I understand what point you're making. When I look at what you said here:

The first sentence doesn't seem to refer to anything that I said. From the way I read your statement your are talking about several different gray cards. I've never heard of a warm or cool gray card. You can have a warm card that is a shade of cyan, or blue or green and you can use these to get different results that could take middle gray as a starting point. All gray cards (if they are really gray cards) are by definition neither warm or cool --- they are neutral (equal values of RGB). So do you see where my confusion over your remarks stems? Are you saying something else, and I'm just missing it.

Here's an interesting test (I'd do it myself, but I just have 1 grey target):

1) Set your Macbeth card on top of the Photovision target. So we can see both "18% grays" very close to each other.
2) Meter the scene and then shoot 3 photos, changing only CWB
2a) CWB using the Macbeth 18% area
2b) CWB using the Photogivion 18% area
2c) CWB using the Expodisc
3) Process the RAW images without further adjustment other than the CWB

Sample the greys in all photos. Does the average RGB sampling of the Macbeth 18% gray target match that of the Photovision? They are likely to be a bit different. If they are, they're not really both grey -- and then you already own a warmer or cooler "grey" card -- you just didn't know it.

Note: I switched to grey for this post. I think I like it better!

[r_fredrick_smith]

The test you suggest might be interesting, but I can't make it either. Keep in mind that my Macbeth card is 30 plus years old, and hasn't been stored in a way that would make it very close to a current Macbeth card.

But one fast note on your last statement near the end:

Sample the greys in all photos. Does the average RGB sampling of the Macbeth 18% gray target match that of the Photovision? They are likely to be a bit different. If they are, they're not really both grey -- and then you already own a warmer or cooler "grey" card -- you just didn't know it.

They very well may both be gray, just not the same shade of gray. One gray is not warmer than the other or cooler. If something is gray it means that it has equal parts of RGB. So the gray represented by r128,g128,b128 is gray and the gray represented by r64,g64,b64 is also a shade of gray. One is lighter than the other (not cooler or warmer). Cooler or warmer would mean that the rgb values were not equal. So I don't believe you are using these terms in a way that avoids a certain amount of confusion.

Cheers,
rfs