How to master white balance?

[Helen B]

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18% gray is R=209, G=209, B=209.

That's about 18% down from white - ie about 82% reflectance. What is commonly called an 18% grey card is 18% reflectance, and after applying an sRGB or Adobe RGB profile it generally translates to around 118 to 120 - ie roughly half way between 0 and 255. That's because it is considered to be perceptually about half way between white and black, and both sRGB and Adobe RGB use perceptual scaling.

Just to be technically correct here:

One of the biggest misconceptions that photographers have - based on what others state as fact - - - is that a gray card is designed to be used to obtain correct White Balance settings. Gray cards are 18% gray and were designed to determine "Exposure" settings of normal caucasian subjects or grassy areas in landscape, that fall roughly into 18% gray tonality. A gray card is not neutral in colour.

It should be neutral, or close to it if it is called a grey card. Even the ones that are marketed for exposure should be neutral, for good technical reasons. Not all grey cards are designed for exposure, some are indeed designed for white balance. Grey cards that are marketed for white balance should be (and usually are) fairly neutral - as neutral as good white cards. They need not be 18% grey and often aren't - they are often lighter.

(As an aside, one of the earliest grey cards designed for exposure, the Neutrowe from 1939, was 14% reflectance, because this was found to correlate the best with the average reflectance of the test scenes that the researchers used. 14% is still considered a good value for 'average' scene reflectance.)

 

[Helen B]

The answer is so easy, but people fight it. Use a ColorChecker Passport. Done.


It's easy, but it involves some steps and it requires you to shoot in RAW and use Lightroom. It also requires you to purchase the Passport, which is about $100. The reason color is a problem is not only because of monitor differences but differences in how cameras record color. White balance is only part of perfect color. Even two copies of the same model can record color slightly differently. And cameras struggle particularly with blues and purples. When you take a shot, do you later have perfect memory of exactly what each color should look like? You can spend time getting it to what you think is good, fiddling with WB and sliders, but it won't be perfect. If you don't have a perfect color memory, how could you edit to match the colors you shot? What is the exact purple of the bridesmaids' dresses? What is the exact pink of the flowers in the bouquet? Exactly how white was the shirt, or did it have a slight tint? How red was that tulip? Even if you had a sample of the color in front of you, how would you edit to match it on screen, and how much time would it take to match each shot to each sample manually? Is close good enough for you? You'd just be guessing. Also, with JPEG, the camera makes decisions about color and applies its own color spaces and default profiles, which are not as good.


The Passport enables you to fix this automatically. It gives you a white balance target for starters. It also enables you to create a profile for the given spectrum of light. When you apply the profile in Lightroom, you can see the colors snap into place. Then, if you have a calibrated monitor, you can hold the ColorChecker next to the image of the ColorChecker on the screen and it will essentially be a perfect match. So, once you create your profiles, perfect color is a matter of two steps: clicking a WB patch and applying the profile. You can then sync the profile and WB across a group of images. Go to xritephoto.com to learn more.


If you don't have money for a CC or LR, get a white card. Use the white card to create a custom WB in camera. This will get you close but not as good as the ColorChecker. White balance and color profiles are not the same. The color profile applies to a given spectrum of light. Daylight is daylight. So one profile covers it. The WB, however, may change at different times of day or in different locations. RAW makes it so much easier to perfect color but you can work around it. It just won't be as good.

Remember that Passport does not produce an ICC camera profile, it produces a proprietary Lightroom/ACR profile. There are other ways of doing it. You can produce a true ICC profile using freeware like CoCa and one of the targets CoCa supports. There is also the Datacolor SpyderChekr which is a little more sophisticated than the Passport, but more expensive. It produces HSL adjustment layers. I have used all three and of them, I generally prefer a true ICC profile via CoCa. These are not the only solutions, but they are three of the least expensive.

 

[amolitor]

I woke up this morning and realized that if you truly color profile your camera, you are now color managed from "reality" color space to the print, back into that same notional "reality" color space.

What's interesting about THIS is that while it probably lets you make the bride's dress white in the print, or the shampoo bottle print out at exactly the manufacturer designated Pantone shade, what will happen by default is that the bride's dress prints out the color it actually was. That's quite different than what the "your white balance is off!" crowd think color management is for.

Making the whites come out white is one thing, and while TPF tends to push it a little hard, it's not stupid at all.
It's also not the same, at all, as making the colors come out accurate.

ETA: Under the harsh light of coffee, I see that this still ain't right.

You're always profiling the camera plus a lighting arrangement, whether you use a white card, grey card, or some color chart plus software. So I see at least two quite different things you can do:

- profile your camera under a reference light source, and just use that profile. This will, modulo a suitable reference light, let you easily make prints that look just like whatever it was, light temperature, local color shifts, reflected light and all. This is what I called accurate above.

- profile your camera under the actual lighting setup you're using to shoot thing (Helen, is this you?) which will let you make prints in which the shampoo bottle is by golly the pantone shade of the pigments the bottle people put into the plastic. This does NOT automatically correct local color shifts. The red apple is going to reflect red light onto the white vase, so that part of the white vase still looks pink.

The latter is what a white/grey card approximates.

I tend to think that some middle road is actually what looks best, generally. I have a vague theory that we pick up on lighting cues from pictures, and our visual machinery corrects colors (and expects to) in pictures the same as it does in real life, but in a muted and mild fashion because we're one step removed from reality. So the white dress in the shade should be pushed away from blue, but you need to leave a little in there so that we don't think it looks weird.

This is rather self serving, though, because I also believe firmly in just dorking around under the command of my own superb taste and visual sensibilities until it looks right. This process, it is clear to me, is vastly superior to your fancy Technology and Algorithms.

 

[Helen B]

The only time I really want colours that are as accurate as possible is when I am in controlled light, so I make the profile in that light. Depending on which method you use to profile, you may be able to apply the profile to other light sources. The profile is usually applied after white balancing, because the raw data need not be used to create the profile. Sometimes you have the ability to make the profile from two sample images - tungsten and daylight, for example.

In practice it is often something of a fool's errand, because the difficult colours get so mangled later in the process when they are squeezed into the display / printer colour space and we end up matching the CMYK proofs to the object itself, or as near as possible. (Getting a good spectrographic sample of a 3-D glossy object is not easy - the eye does it best.) It's still good to start with the best you can manage, if accuracy is important. Oh, and camera profiles are rarely the perfect answer to everything - they have to be made from a chip chart that has its own limitations.

The reflections of coloured light from other objects does cause a problem, as you surmised. Glossy dark-coloured surfaces can sometimes be an even bigger pain than polished metal in this respect - ie picking up the surrounding colours. If possible I use white cards to prevent these problems and I confess that I comp in parts of extra images shot with white cards that would be in frame just so that the colours are unpolluted by the surrounding objects. Some seemingly simple images are composites of ten or more source images just for the reason of avoiding colouration from reflections.

 

[amolitor]

I know a guy at EFI and he agrees. Color management is all very fun, but there's so many moving parts to get to the final print that someone's gonna drop the ball. You work like a dog and get it all perfect, and then some dope buys a trainload of paper that's a different shade and 750,000 issues of the magazine are printed out with your ad plus an attractive yellowish cast.

Still, one does one's best, right?