What is White Balance?

[hwchoy]

I wrote this blurb for newbies at a gardening place. Repost here for all to read, and please comment on any inaccuracies or misconception.

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What is White Balance?

Simply, this refers to how a camera knows what colour it perceives via its sensor, is to be considered as "white".

To be more technically accurate, the camera needs to know what colour is considered "tonally neutral". When it knows this, it can then adjust accordingly all other colour values to compensate for the colour cast a lighting source contributes to the subject's actual perceived colour.

What is Tonal Neutrality?

Colours are the additive composition of three primary colours (red, green and blue). We say a colour is neutral tone when it comprises equal amount of red, green and blue. This would include pure white, pure black (no colours at all), and all neutral grey colours (i.e. equal amount of the three primary colours in varying but equal intensity).

Custom White Balance

For example, if you photograph a white object which is illuminated by red light, the object will appear reddish. You know that the object should be white, but the camera does not. In order to tell the camera that this is actually a white object that is rendered reddish due to lighting conditions, one need to perform a custom white balance process. Most advanced cameras support this.

To do this, you need to find an object that YOU KNOW is neutral tone. For professional purposes, one would use a white balance card, or grey card which is carefully manufactured to be 18% grey (i.e. it reflects red, green and blue in equal amount, at 18% intensity). I am not sure of the technical reasons why 18% but presumably this is the optimal level for the camera or film perception.

Now this white balance card is illuminated by the light source you intend to use to take the photograph. So if your light source is incandescent bulb which has a yellow cast, the card will no longer reflect the three colours in equal amount since the light source has more yellow (red and green, than blue). But the camera has been told BY YOU that this object should be tone neutral, hence it is able to figure out how much the colours has been skewed due to the lighting, and adjust accordingly for all colour values that it perceives.

This is what we call White Balance customisation, or calibration.

Before and After

Here's two pix from Eugene to demonstrate the results of a custom white balance:


Before




After

[hwchoy]

Here is what a set of white balance cards look like. The grey card in the middle is the 18% grey tone neutral card. The others are engineered to be slightly off neutral to be "warmer" (i.e. more yellowish) or "colder" (i.e. more bluish).

[valice]

For fish photography, which card you prefer? The grey card still?
I somehow prefer to use the minus green card to remove that green tint which I always seemed to be getting when I transfer the photos from the DPP to Photoshop.

Just to add on, white balancing is very important for aquatic photography when using a flash system which is placed above the subject. This is because, depending on the colour and type of substrate used in the tank, a certain colour cast will be created. One example is ADA Africana. Fishes shot in tanks with that substrate seems more yellow than using ADA Amazonia.

Doing custom white balance is useful in saving time spent in post-processing to remove colour casts or correct wrong colours in a photo.

[hwchoy]

the grey card is not water proof, so I used the back of one of the other cards. it doesn't matter very much since the tank environment is so variable. as long as WB is approximate the rest you can adjust in photoshop.

[Shadow]

Sorry I'm confuse, so how do you do that? do you put the target card in water under the aquarium light and adjust the white balance on the camera so that card picture shown in the LCD white?

[hwchoy]

depending on the procedure of your camera. typically is that you take a picture of the card under the intended lighting (whether aquarium or flash) at the general position where you expect the fish to be shot.

then in the camera menu you switch to custom white balance mode, and indicate this picture as the one to be used as the white balance reference.

[Shadow]

Can I use white color A4 paper instead?

[hwchoy]

yes can use white paper, aga aga.

[Wackytpt]

Choy,
I convert this thread to a sticky thread

[juggler]

Good info, Choy! I learnt something today.
Thanks!

[StanChung]

18% tone refers to a what a standard averaged picture exposure would be if i remember correctly. A fair skinned Caucasion person is 36% tone. this means we have to overexpose one stop to get the right exposure for a Caucasion. [sorry out topic] [depends on the lighting mood as well- high key medium or low]

[trident]

Choy,
Intertsing topic.
I always use the auto white balance in my camera (Fuji S6500fd), due to the aquarium lighting sometimes it comes out pinkish or yellowish. So in this situation would it be best to calibrate the white balance first before shooting?
Thanks
Richard

[Shadow]

Me too, always auto. the photo comes out yellowish like green water

Will try to laminate white A4 paper, make it water proof, and use it as white balance target.

[hwchoy]

Choy,
Intertsing topic.
I always use the auto white balance in my camera (Fuji S6500fd), due to the aquarium lighting sometimes it comes out pinkish or yellowish. So in this situation would it be best to calibrate the white balance first before shooting?
Thanks
Richard

yes, go through the process and set it as your custom white balance while shooting. read your camera manual.

[luenny]

Richard and Robert,
Before going on and trying the to make your own white paper, if you don't have the necessary tools, what you can try is to try to take pictures with all the different white balance presets that comes with your camera. Sometimes, certain presets is close enough to make your picture look white instead of greenish. This is not the real fix but it's a cheap and nasty way to get decent photo - for lazy people who don't have a real camera - like me.

- Luenny

[trident]

Luenny,
Thanks for the tip. Looking forward to try it out.
Trouble I faced is when water is a bit yellowish,
due to medication, the photo will turn out greenish.
Richard

[StanChung]

Lol, Richard, then you need photoshop or something similar to rid of it. If the water is already yellow, you most probably can't fix it in-camera unless your is sophisticated enough.

[trident]

Stan,
Sometimes water is a bit yellowish, but the photo turn out green.
I have not thought of using the WB before, now can give it a go and
see how it turns out. Have not learned to use photoshop yet, anyway
it's expensive. Most likely go with Gimp, it's free.
Thanks
Richard

[StanChung]

Sounds like a good alternative, I haven't learned how to fine tune the WB myself. lol. Press a few buttons and see if nice and like Luenny says, check the lcd colour.

[hwchoy]

custom WB will fix water staining (as long as not too severe) and colour cast from lights and leaves.