White balance questions

[CJK]

Hello, after reading the tutorial on white balance I have a few questions.

I have usually just stayed in auto, with occasionally using cloudy. I want to get away from auto and understand wb more.

First, since I shoot in RAW, does the selection even matter? Will I be able to do everything in post-processing?

Since I want to get out of auto, is buying those cards a good idea? How do those of you who use custom and the cards utilize them? Before starting your shots do you calibrate with the cards? If so how often do you have to do that since the light is constantly changing. If you set up for a sunrise/sunset, the amount and intensity of the light is changing almost every second, what would you recommend on terms of wb, especially if you are using the cards to calibrate.

[Geoff F]

With modern cameras, Chris, auto white balance usually works well and is particularly useful when shooting various subjects in changeable lighting conditions.

Raw images can easily be adjusted during conversion. Providing you have a good eye for colour and after gaining a little bit of experience.

Using the Sunny/Cloudy, etc, white balance settings will sometimes get you closer to correct white balance but usually not perfectly; so some extra adjustment is needed.

A card, in various forms, should give correct settings, providing it is used correctly but there is always a risk that conditions change and you don't make a new reading. Or like me, forget to cancel it later.

If shooting Jpeg, these options are far more important, and a card really is worth doing.

Setting a Custom White Balance isn't particularly difficult; but it can become something of a chore, even if it only takes a minute or so. Simply a case of shooting the card then going into your camera menu options and tweaking a few settings. But I can still get that wrong!

So what do I do? Nearly always, I shoot with AWB but in Raw format then adjust the balance during conversion. Quite often, I am not fully happy with the 'correct' balance anyway and want to vary it a little warmer or cooler.

[Polar01]

Chris: as Geoff has stated today's camera WB are very good indeed so leaving in auto works perfectly 95% of the time. It is when you get into difficult lighting conditions that a card comes in handy. Just a short time ago I was shooting for a gallery opening of a young artist, I asked her to hold the card and stand beside one of her paintings I told her that I wanted to get the right colour balance for the lighting used to make sure that I go her art work correct. She agreed that it was more important to get make the work look good not her (she sold $24,000 that night). The other place I use a card is shooting in a church which can have some of the more weird light seen, so anything to get close helps.

Cheers:

Allan

[pnodrog]

Shooting RAW you may as well leave WB on auto. Depending on your conversion software it will either be ignored or used as the starting WB. In either case you will be able to adjust it fully during PP. Setting WB and fiddling around with cards to adjust WB may improve accuracy but has nothing to do with aesthetics which for most photographs is far more important.

[Mike Buckley]

Shooting RAW you may as well leave WB on auto.

I think that depends on the quality of the camera's auto white balance. Though it's really great on my primary camera, it's not very good on my backup camera, which is an older model. I never use the auto setting on the backup camera because doing so invariably adds an extra step during post-processing to correct the white balance.

[Dave Humphries]

Hi Chris,

When the light falling on the card is the same as what is falling on the subject (by no means always the case), why not just shoot a shot with the card prominently held/stood in shot (in AWB) and during RAW conversion; colour pick to make it grey?

The Kelvin + Tint figures that gives can then be applied to all the other shots in the series.

Well that's how I do it - when I remember - and when I don't (or can't be bothered); since the camera remained on AWB, no harm done.

For sunrise/sunset, the last thing you want to do is neutralise the lovely colours, which you may if you AWB, use a custom preset, or my method - so this is one time when it should be set to "sunny" or "cloudy" and left alone.

Cheers,

[CJK]

Geoff,
Thanks for the tips, that makes sense. I was wondering since I was shooting RAW if it really mattered if I was going to be changing things in CS, although getting it close is always a better route so you'll have less to adjust.

Polar01, good tip about churches, they do always seem to have odd light going on.

Pnodrog, thanks, thats what I was thinking too but wanted to ask since I had no idea.

Mike, I have no idea about my camera and its ranking (Nikon D5000). I know its not top of the line but I figure its decent.

Dave, thanks for the tip about the golden hour times, makes sense. Good idea about the AWB and if you forget, no harm done... Im usually messing around with everything else and getting lost in the scene anyways, its hard to remember everything every time!

Thanks everyone


Cheers!

[drjuice]

Just a suggestion, CJK. Absolutely yes it does make a difference with RAW. I use a freebie to process RAW to TIFF and I generally take one image using AutoWB and a second using my choice of WB, because I too am trying to understand WB better. In general, I have the freebie software (DC RAW) process the AutoWB versions, in general, absolutely perfectly for my eye. I rarely use the image with my choice of WB.

Hope this helps.

virginia

[Brev00]

For me, being able to adjust white balance in post has opened up a whole world of possibility. I shoot in daylight wb most of the time because, well, I shoot in daylight. Many prefer to shoot in cloudy, but I often like a cooler home base and adjust it warmer if I see the need. I do not use a card. Instead, if I want accuracy, I use the white balance eye dropper in Adobe Camera Raw. I find something that should be white and adjust it manually or with the dropper to be neutral. While I often do shoot for accuracy, my primary consideration is aesthetics: what white balance really gets the image to where I want it to go. That might be cooler, warmer, or plain, old accurate. Since there is so much room for change, I like to start from a fixed point--daylight. I guess I feel auto white balance is like auto iso or auto mode. I really never use awb. In tough, artificial lighting, I will approximate the white balance using guess and check: take a few preliminary shots and adjust to find a specific kelvin I am happy with. That will still be adjusted in ACR.

[CJK]

Thanks juice and brev, I have never tried messing around with the white balance eye dropper in ACR, looks like I have another thing to learn.

[Inkanyezi]

Auto white balance? From what?

There is absolutely no way, physically, a camera can truthfully adjust white balance automatically. The caveat is that the camera simply does not have a sensor for the task, and moreover, it cannot assess the light source, as the only optical element where light enters the system is pointed at the scene, not at the light source.

Several years ago, there were many compact cameras that actually tried to white balance the images from the scene, which resulted in magenta coloured gravel paths in parks and orange coloured walls of white washed buildings where the sky took up much of the image area. So with later models, camera manufacturers have mostly resorted to a better approach, which more often does a better job. Auto WB simply is daylight setting with many cameras, although there are a few models that attempt to balance for tungsten, when the sensor finds typical colour shifts that result from tungsten lighting.

Essentially however, it is a fact that the camera does not have a sensor that measures the light illuminating the scene. No camera has it, absolutely none. Hence there is no camera that can set a correct white balance automatically. However, daylight white balance is a good approximation for most daylight situations, and that's it. Many cameras, when set to AWB also stick to daylight when shooting under tungsten or trickier conditions.

White balancing is more than setting a K value. The K scale in itself has an inconsistency, in that from zero to 4999 K it relates to a smooth spectral curve with its top in the red part of the spectrum, while from 5000 K and up it relates to an uneven "daylight" model, supposed to give "true colour rendition" for daylight viewing. These are two essentially different spectral curves, and in reality, we may experience many other mixes of light, that should all be accommodated into the tri-colour sensitivity of the sensor, and later being reproduced by some viewing media, either with subtractive or additive colour of varying quality.

Colour rendition of light sources is often presented as a Ra-value (CRI, Colour Rendering Index), which relates to the two different spectral curves of either the black body (tungsten) or daylight (5000 K and over). Black bodies are fairly straight forward. Their spectral curve is smooth, and they invariably have poor rendition of blue to violet colours. The CRI is not a measured entity, but an evaluated one. A board of real people evaluate colour rendition according to a standard, from a patch chart with various colours. One chart is illuminated with either "daylight" or "black body radiation", and the tested light source is illuminating the other chart. The index is a comparative figure, a higher index indicates greater likeness, coherence, between the two charts illuminated by different sources. As the incandescent filament essentially is a "black body", CRI of incandescent light sources always is presented as Ra 99, although it could as well be regarded Ra 100. An incandescent Ra 100 light source will render colours as any other incandescent source, poor in the violet-blue part of the spectrum, while daylight in contrast is rich in all parts of the spectrum, although weaker in green. Incandescent light can be corrected with a parametric filter to produce a more daylight-like rendition, with weaker green and better blue to violet rendition. The filter mostly used is neodymium oxide, with a purple tint, and the CRI of neodymium incandescent lamps is in the region of 60 to 70, although they render far better, more neutral, colour, unless you really want the "feel" of incandescent.

In essence, however, we have only three colours to play with, red, green and blue, and the mix of these is what we use for setting white balance. We may complicate it a bit more, by balancing differently for different luminance, using different gamma curves for the three colours. Mostly we don't want to do that, but balance the three of them within a region where they are almost linear functions. To do this with reasonable accuracy, we need a neutral target that is exposed somewhere in the brighter part of the luminance curve, as zone VII.

Mostly we don't need exact white balancing, and often we prefer a more casual approach. Very often, we don't even want a "true" neutral colour balance. However in many technical photographic applications, where consistency is important, white balance has to be taken seriously.

[rpcrowe]

I always shoot RAW often use a WhiBal card in the scene. Michael Tapes' tutorial video tells how to use the WhiBal card.

http://www.whibalhost.com/_Tutorials/WhiBal/01/

To tell you the truth, I am not absolutely sure just how accurate we need to be (product photography and artwork photography excepted). I often use the white coat of my Maltese dog subjects as my white balance target with very decent results...

[Inkanyezi]

Artwork photography is a rather complicated task, when it comes to lighting and white balance accuracy. Product photography is a lot simpler, as it doesn't usually call for a "true" or "neutral" white balance, but relies heavily on consistency. Therefore, for shooting products that shall be presented in catalogue form or for publicity, the important matter often is to use the same kind of lighting. That is a good reason for always using studio flash when doing this type of job commercially.

There is a common misunderstanding among photographers about the light quality of electronic flash, essentially xenon gas discharge lamps, believing that the spectral curve is smooth with no dips or spikes. Discharge lamps, or any light source that excites atoms by ionisation, will NEVER produce a smooth spectral curve. This includes our beloved sun, which is a huge nuclear reactor, emitting a full spectrum with many dips and spikes. So, a smooth spectral curve is moot, and there is no need for one. Electronic flash does not even have the same spectral quality for different energy output. Small strobes as the ones built into many cameras mostly are far more bluish than larger ones, as studio flash heads.

A smooth spectral curve is moot. We have three colour filters in front of the sensels: red, green and blue. All of them leak other colours heavily, so each sensel also receives colour from the rest of the full spectrum to a varying degree. Our RAW conversion software, whether in camera or in the separate computer, sorts this out to be presented on a tri-colour presenting medium, our computer screen. Later on, other software is used to convert the additive image for subtractive printing, which is often done with more dyes than three. Just as the coloured filters in front of the sensor are not "clean", the emission from our tri-colour computer screen is not pure for red, green and blue, but we are used to seeing colours on those screens, and we imagine that they are like colours in nature, which they are not. The impression in our brain however may, or may not, be identical. Colour does not exist in nature, only different spectral emissions. Colour is a construct of our brain, comparative values from our vision cells in the eye.

As Richard, I use the WhiBal to set colour balance, when I want a good starting point, as when I take product shots. Grey cards are useless for the task; my Kodak grey card is not neutral. WhiBal is not a grey card, but a white balance reference, a spectrally neutral reference card. It is not 18% (or 16%) as grey cards for exposure, but brighter. When included in a correctly exposed scene, it will fall in zone VII, containing substantially more data of each colour channel than a grey card, which will fall in zone V. More data means better precision. The card is used only for setting colour balance, not for setting exposure.

When using the card for setting white balance in the camera, you spot meter the card with plus compensation of at least one stop, but maybe a bit more, depending on what camera you use. Two stops is too much for most older cameras, but one and a third is safe with all cameras. Or set exposure with the grey card, incident or from the scene.

And if convenient, use the white fur of your lamb, cat, dog or whatever you think should be neutral in your image.

[Mike Buckley]

When using the card for setting white balance in the camera, you spot meter the card with plus compensation of at least one stop, but maybe a bit more, depending on what camera you use. Two stops is too much for most older cameras, but one and a third is safe with all cameras. Or set exposure with the grey card, incident or from the scene.

Regarding the part I provided in a bold font, I think you meant to mention exposure, not white balance.

[Inkanyezi]

Regarding the part I provided in a bold font, I think you meant to mention exposure, not white balance.

No, not at all, but exactly what I wrote, only exposure of the white balance target. You should by preference expose your white balance target so that it will render a rather bright tone, regardless of its relative brightness. I.e. if your target is white, light grey or darker grey, you should preferably expose it so that it falls in zone VII. It does not relate to what exposure you will set for the scene. If for example you use the WhiBal® and expose for the scene, it will fall in zone VII as it is a rather bright grey. The card is made for white balancing, and it is not bright white for that very reason. It should not become too bright in the image.

Also, you might note that the white balance target should not land too high in brightness, because you need to have it within the straight part of the gamma curve. Zone VII is best in this regard, plenty of data bits and still within the straight slope of the gamma curve. Therefore, a white target that is rendered white in the image is often unsuitable, as it might lie on the shoulder of the gamma curve for one, two or three colours.

The confusion might stem from most people's indistinct usage of the terms "grey card" and my particular usage of "white balance target", distinct from "grey card". Those are different concepts. The grey card was conceived before most of us used colour film. It was never meant to be absolutely spectrally neutral, but had a density that was suitable for gauging exposure. The white balance target, where WhiBal® is an example, is only for white balancing. When exposing for the scene, a grey card should fall in zone V, while the white balance card is preferred to have more data bits for precision, while still falling in the straight part of the gamma curve, thus in zone VII.

[Mike Buckley]

Thanks for that explanation, Urban. I have often read that an incorrect exposure does not affect a white balance reading and that's apparently a myth.

[Inkanyezi]

If your white balance target is rendered very dark in the image, there are few data bits, and the resulting white balance may be off for that reason. If the target is too bright in the image, it will not fall within the straight part of the gamma, and that may throw off the white balance.

Most camera manuals state "correct exposure" for the white balance target, which will place it in zone V, as that's how the meter is calibrated. Mostly this is OK, but compensating with plus one will take in more light and give the computer many more data bits. If you compensate too much, you might drive exposure to the unlinear portion of the curve, and +2 is too much with many cameras.

So it's not really a myth that "incorrect exposure" may throw your white balance off, but what exactly is "incorrect" then?

One good example is when you want to use the overcast sky for balancing. In your final picture, you might prefer it to be washed out, but when you use it for white balance, it must fall within the straight part of the gamma curve.

And maybe it isn't much of an issue if the WB target would fall in zone V. Michael Tapes is meticulous about white balance, so he prefers to have it a bit brighter, so that he gets more data bits. The target should be somewhere on the straight part of the gamma curve, and he made his choice, so that the WhiBal target can be used for balancing when it is included in a correctly exposed scene. Before I got the WhiBal card, I used a white target, and I had to expose it to make a grey rather than white in the image.

So it boils down to having your target rendered within the straight part of the gamma curve, preferring to have it brighter than middle grey.