White Balance (aka neutral balance and grey balance)

The very lazy MinCat has decided to follow through on her promise! To begin with, look at this post, where I whine about white balance.

Whaaa....? you gurgle, wossat? Yeah, I know what you mean. Until the day I just could not get the colours right on one of my photos, I always ignored it. Well, I had also started shooting in the NEF (RAW) format, which meant I could do more twiddling with the picture, so I also wanted to learn about it.

So what exactly is white balance? 
Used, as we are, to the human eye and its miraculous processing of images, we don't realise just how many things it does inside our heads before we register an image. For starters, it can have so many distant bits in focus at the same time. It also fiddles with contrast and the like to make sure we get silhouettes or fingers of god. One more thing it does it make sure white is white, or grey is grey, so all colours look normal. It's only when we try and replicate these things with a camera that we can literally see the difference. Like below:

Essentially, the key here is the colour temperature. Scary though this might appear, it simply means the range of waves emitted by an object, assuming it absorbs all other light coming into it without changing it in any way. (This is important because thats the only way we know that the light, and therefore the spectrum of waves, coming out of the body is wholly intrinsic to the body itself, instead of being, for example, the light reflecting off your glasses.) The higher up the scale that the range is, the bluer the light, and the lower down the scale, the yellower. So called white light, or neutral light is essentially a replication of daylight - personally I think of it as a mixture of white and yellow, and have also found that such a mixture gives the best approximation of daylight.

This light, in the picture, is a yellow bulb. This means, it emits more yellow light than any other kind, which means it should leave all objects with a tinge. It does indeed, only the human eye sorts that out, leaving my blue curtains blue. The camera, however, cannot do that, so it makes the curtains a sort of steel grey. Once I adjusted the white balance and colour temperature, however, they curtains looked blue again, like they do to my eyes. This can totally ruin a picture, especially a low-lit or a specially-lit portrait. Sometimes the sun can affect your landscape pictures too.

Most of the time white balance is automated by your camera, and it's only occasionally that you need to fix it yourself. The advantage of shooting in RAW mode is that you can fiddle with the balance after you've taken the shot; while shooting in other modes mean you have to try and set it before the shot. Imagine you're taking that picture above without the RAW option. What can you do to make the white balance work?

For starters, you could scroll through the white balance options on your camera, and pick one that gives you the most realistic result. Enough experimentation with the same object in the same light will give you a good understanding of how your camera works. Another option is to include a grey or white object in the frame, which should give the camera a clue about what the neutral colour is, and then the auto white balance will work. However, it's not always possible to do that, which is where the other methods come in. If you haven't managed to fix it before you shoot, then your best bet is to fiddle with the colour temperature while in a photo editor like picasa or GIMP. (More on those guys later.)

Here is a nice tutorial that's more technical, if you like. If you want more, there's always our dear friends Theodore and Evadne Google!