Had a discussion with a colleague, wanted to gets others' takes on it.
I think I don't need a grey card for anything. I think Chuck's white towel will do. Am I wrong? I mean, getting a custom white balance setting, is where anything a grey card can do that a white towel cant, as long as the towel is really white?
And for setting exposure, Chuck's method of exposing for the tiny blinkies on the white towel seems to work brilliantly. What else can a grey card do for me?
This may be stupid, but I do not carry a white towel around with me.
I use a collapsible grey card that has a white reflector on the other side, it is waterproof and compact.
I could not imagine walking onto a set and asking one of my models to hold a towel while I set my white balance and exposure levels, that is what my gray card and light meter are for.
This may work in a controlled environment, but when you never know where you will be shooting I think a grey card makes more sense.
speedtrap wrote:
This may be stupid, but I do not carry a white towel around with me.
Sure- practical matters aside, I'm asking from a technical perspective. I know a grey card will fit in your wallet, and a towel won't. Just wondering if 18% grey is better technically than white with details.
Apparently anything white will work . . . I used to be interviewed on TV a lot, and one time I showed up on the set & the photographer scrambled to find something white & handed me a sheet of paper. After he did his WB check, I glanced at it, and it was an 'adult content' e-mail someone had printed off. I cracked up. One of the names on the header was the news director, who was a colleague of mine, so he got a lot of pain from me for that one.
Erik Moore wrote:
Had a discussion with a colleague, wanted to gets others' takes on it.
I think I don't need a grey card for anything. I think Chuck's white towel will do. Am I wrong? I mean, getting a custom white balance setting, is where anything a grey card can do that a white towel cant, as long as the towel is really white?
And for setting exposure, Chuck's method of exposing for the tiny blinkies on the white towel seems to work brilliantly. What else can a grey card do for me?
The point of using a textured white target is to have something simulating "the brightest highlight that must retain detail" to be sure the detail in that tone is not blown out. A gray card can't do that.
I use a white plastic card with an embossed texture in place of the white towel. I stole it from a cheap bathroom cabinet.
Need one? No you don't. They are useful in some situations. I use one once in a while, not yet this year however.
It's another gadget to mess around with.
18% grey is not necessary for white balance (anything grey or white will do, as long as it really is grey or white) but there's a big difference between using a white towel and a grey card to meter.
Yes, often the towel will work, I'm not saying it can't. But all a towel really does is tell you when your highlights are clipping. It gives you no clue as to what your settings should be to obtain a properly exposed diffuse highlight (I'm basically regurgitating Dean Collins' stuff here). There will be times when properly exposing the part of your subject that you want properly exposed will result in some blown out highlights or shadows without detail or both.
Ideally you want everything within the range of your sensor but in some lighting conditions that's just not possible. Say you've got a very strong back/side light (rim) from the sun. That will most likely clip some of your highlights if you properly expose the face, for example. If you stop down until the white towel is no longer blown out at the edge you'll be underexposing the face - maybe not a lot, but it will likely happen. I know it's a pretty specific example, but it's a common scenario.
If you have a light meter try this out (I'd actually be interested to know your results):
Using only the ambient (no cheating with flash ), rim light your subject with the sun (angle is up to you). Using the "towel method" set your exposure and take a shot. Next, use your incident light meter to find the proper exposure for the face, which should only be receiving fill light from your surroundings. Be sure to do this quickly to avoid having the light change much.
So? How do the two compare? My hypothesis is that the light meter will tend to give you a brighter exposure (wider aperture, slower shutter speed, whatever), but let's see your results. My light meter is on the way and I'll add my results when I get it.
The incident light meter works the same way as using a reflective meter (like the one in your camera) on a grey card. Just wanted to mention that before someone gets on my case for comparing meters and towels when the OP asked about grey cards
Kyle-
I think I understand the point you're making regarding the shortcomings of a towel in that scenario (a wide degree of exposures depending on towel placement, in or out of the shadow), but wouldn't a grey card have the same weakness?
I don't have a light meter, so I cant try your experiment, but it seems to me that the effective difference in readings between a towel and a light meter would depend entirely on where/what angle each was held in the scenario you describe. Or am I missing something?
The towel is simply a proxy for judging when textured highlights you can't see in the camera feedback, like eyes and teeth, are correctly exposed. Its unlikely a towel will be perfectly neutral. The important thing is that its similar the reflectance of the white details where detail is needed. If the subject is wearing white clothes there isn't any need for the towel. But coincidence the red channel in skin, which also can't be seen in the feedback, also clips the same time as the towel making it a good quide to avoid blowing skin highlights if held next to the face when setting portrait exposure, even if also using a meter. The towel is like the canary in the coal mine used to warn the air is getting bad. if I see the towel or any other white textured highlight clip in camera warning when "chimping" it tells me I'm at the cusp of losing highlight detail in the RAW file. With experience comparing the camera warning to the RAW files its easy to corrolate the two.
An incident meter can't account for variables like lens flare and a meter is only accurate if compenstated to the true speed of the camera, so even when a meter is used its a simple way to verify the meter reading is producing correct exposure. Like Reagan said about the Russians: "Trust, but verify"
A gray card is a process control guide for White Balance. There are many ways to set WB, but the only practical why to measure it in editing is from the RGB values on an object known to be neutral. For example you can use and ExpoDisk to set WB, but there is no way to verify it is actually neutral unless a known neutral gray card is put in a test shot and measured. Also with a gray card in a test shot its possible to "click to neutral" on one image with the card then paste the WB settings into other RAW files taken in the same light. Setting Custom WB off the card makes the color neutral on screen when opened but doesn't alter the RAW capture, saving the copy / paste WB settings step.
The reason WB better off a gray card rather than a white one are:
1) Gray cards are manufactured to reflect equal RGB in all light. Even the newer Kodak ones (contrary to what some say).
2) With a white card there is a chance overexposing it might clip one or more channels which would skew the WB. Gray falls in the middle of the sensor range so that's less likely to happen.
What the process does is ensure all neutral tones are reproduced neutral (i.e. gray balance) and had it called "gray balance" instead people wouldn't be as confused about it
Erik Moore wrote:
Sure- practical matters aside, I'm asking from a technical perspective. I know a grey card will fit in your wallet, and a towel won't. Just wondering if 18% grey is better technically than white with details.
Thanks for your input.
Erik,
Grey cards serve two very different functions in the digital world. First, is for exposure as in the film days. Second as a White Balance tool. Larger collapsible cards can even offer a third function as a reflector or cutter.
From a WB standpoint there are indeed some technical differences, as small a they may seem. Most (not all) digital grey cards are a true neutral RGB, where the component color values (Red, Green, Blue) are equal. Most white cloth, including terry cloth towels and T-shirts, have brighteners in them. Brighteners increase the blue component of the RGB values, resulting in a slight color imbalance that is visible to the camera, if not our eye.
Although different camera companies recommend either white or grey for white balance calibration, both will work as a WB reference because they are both monotone colors. Grey tends to handle a wider range of exposure variation because it is mid-tone.
Although it is not as color accurate as a true digital grey card, terry cloth certainly can work as a WB tool , but it's main benefit is more as a exposure tool than a WB tool. Terry cloth works extremely well as a highlight warning indicator where texture helps to establish the point where highlight detail is lost.
The value of a "grey" card in the digital world may be as debatable as a light meter, but as a "workflow" tool it certainly has it's place, particularly if you are shooting processed images, such as JPEGs. I personally find a good quality collapsible grey card with white back to be a invaluable WB/Exposure reference tool and a handy fill card/ reflector as well. But when ever necessary, I won't hesitate to use whatever is available to me. Even in my film days, I'd use the back of my hand instead of a grey card if that's what it took.
The most important thing is to know your equipment, have a consistent workflow and incorporate tools whenever possible that can maximize your efficiency and effectiveness in achieving your goal.
The problem with these types of devices, like the ExpoDisc, is that they work better for general ambient light photography than they do with flash.
Also, you don't have to have a different card for every lens. It's also much easier to drop a card in front of your subject whenever the lighting changes than to fuss around with your lens.
And finally as Chuck points out, "you can use and ExpoDisk to set WB, but there is no way to verify it is actually neutral unless a known neutral gray card is put in a test shot and measured. "
But as they say, different strokes for different folks.
I have done a tremendous amount of testing and analysis on this subject. Conclusions:
1. Every test card I have bought - X Rite, etc has deviations of up to 400°K from the white end to the black end.
2. Every camera I have used has similar disparities from high exposure to low exposure (D300, etc,)
3. Every color temperature meter I have Minolta, Gossen = three or four of them has the same inconsistencies from bright to dim flash.
4. You cannot successfully do an accurate white balance using a "white" card exposed anywhere near white. There is too little resolution for RAW to read when your patch is reading like 220-220-220. You must be nearer the middle of the brightness spectrum - like 128-128-128 for RAW to yield an accurate measure (if such a thing actually exists at all).
The only way I have gotten consistent results was to go to Lowes and grab 10 color patches that "look white", line them up side by side with X Rite card and shoot them at a variety of exposures, compare them to the average of the X Rite cards in RAW and select the best.
Short answer: It doesn't matter if you use white or grey, but the patch must be absolutely color neutral or you're wasting your time. Do not attempt to use w white card exposed anywhere near white - underexpose it about -3 f stops and use the eyedropper in RAW at several points on the patch.
Here is the setup I used. Notice there is several hundred degrees of error between the white X-Rite patch and the next shade. My suggestion is go to Lowes and get the exact white patch in the jpeg, under expose 3f and use RAW.
shatterkiss wrote:
Using something "close to white" will give you images that are "close to white-balanced". It's up to you whether or not that accuracy is important.
i say close to white as in, painted lines(on a field) very close(so they fill the frame), a white jersey, an undershirt and so on
ishootsports3 wrote:
i say close to white as in, painted lines(on a field) very close(so they fill the frame), a white jersey, an undershirt and so on
Right, but all of those are "white", not truly neutral.
If you want to do a test, take a shot in raw mode that contains all of those objects in the same frame, then in your raw editor of choice do an eye-dropper white balance using each of those sources in turn. I'm pretty sure you'll see the overall white balance of the image being noticeably different with each one.
This is why a truly-neutral and consistent white balance target like a grey card is important. It's the only way to know that you're balancing to the available lighting conditions, rather than inconsistencies from target to target.
I am not claiming that your wrong, merely that if i shoot something of a whitish solid matte nature and check a few shots, its close enough. If i shot studio work i would shoot a Grey card. I am simply saying that it works and i get images that look how they should, and if what i measure off of doesn't look right ill fix it.
Erik Moore wrote:
it seems to me that the effective difference in readings between a towel and a light meter would depend entirely on where/what angle each was held in the scenario you describe. Or am I missing something?
That's a good point, and as Chuck mentioned (and others seconded), white terry cloth can be a good indicator for when you're blowing the highlights.
I just prefer grey because it's calibrated to work with my camera's meter's assumptions: that a reflective reading of 18% grey equals proper exposure. Using a towel can be fairly precise, I just trust calibrated tools more. (That is not a dig at anyone who uses the "towel method" or other similar method)
A card can also be used to determine what ratios you're dealing with by placing it in various parts of the scene and taking readings off of it. I guess a towel would work too, but I find that method a little cumbersome when you want several readings or your light changes often throughout a shoot. Plus you have to make actual exposures to use the towel, so you need to change your camera's settings every time you meter.
), rim light your subject with the sun (angle is up to you). Using the "towel method" set your exposure and take a shot. Next, use your incident light meter to find the proper exposure for the face, which should only be receiving fill light from your surroundings. Be sure to do this quickly to avoid having the light change much.