One of the basic tools we photographers have for controlling how the colours look in our images is the white balance adjustment. We set the white balance to remove unwanted colour casts (so that white objects appear white), or sometimes to add a colour cast for creative effect. The concept of white balance is closely tied in with the colour temperature of the light that is illuminating our images. I'm not going to delve into the science behind colour temperature and white balance - there is plenty of information about this subject to be found online. But it is important for photographers to understand how to set the white balance for an image, so a little background is useful.
The quality of light can be described in terms of its colour temperature (measured in degrees Kelvin). A vibrant sunrise with reds and yellows in the sky has a low colour temperature, even though we commonly describe reds and yellows as being 'warm' colours. Conversely a deeply shaded area may be dominated by 'cooler' bluish tones, which equates to a high colour temperature. Pretty confusing, eh? The important point is that the colour temperature of light changes throughout the day and as we move from shaded or artificially lit areas to sunlit areas.
As we go about our day, our brains are continually making small adjustments to the way we perceive colours - the white shirt we are wearing will still look white whether we are standing in a room lit by fluorescent or incandescent lights, or whether we are indoors in the shade or outdoors in full sunlight. The colour temperature (and therefore, the quality) of light differs in each of these scenarios, but to us, white is still basically white. But if we could view our shirt in each of these lighting scenarios at the same time, we would notice that the shirt takes on a slightly different shade of white in each.
Our digital cameras have white balance adjustments so we can choose which white is 'correct' and apply that to our image. If we photograph our white shirt under incandescent light, the colour of the light will add a yellowish cast to the shirt - even though this may be correct according to the colour of the light, it will look wrong to us when we view the image. In order to show the true colour of the shirt, we have to adjust the white balance to remove the yellow cast. We can achieve this by choosing a specific white balance setting in the camera before capturing the image, or by adjusting the white balance later in software.
Of course, if there is a yellow cast on the white shirt, then there is a yellow cast over the whole image even though it might not be so apparent in some areas. When we adjust the white balance to show the shirt as pure white, all of the other colours in the scene will change slightly as well, hopefully for the better.
The same scene at three different colour temperature settings. The image at left is too blue for my liking - the sky isn't too bad but the sunlit rocks and sand have lost their vibrancy. The image at right has plenty of yellow/red colour in the rocks and sand, but the sky has turned an unpleasant grey tone. The central image is a good compromise to my eye and is closest to how I remember the scene - there is still a nice blue tone in the sky to create a pleasing contrast with the sunlit rocks and sand.
Most digital SLR cameras give us three basic choices for setting the white balance before we capture an image:
Auto white Balance - the camera chooses an appropriate setting based on an overall appraisal of the colours in the scene. How well the camera does at selecting an appropriate white balance setting will vary depending on the scene and the colours and lighting it contains.
White balance presets - you choose a setting such as shade, daylight or sunset to match the prevailing light conditions. A downside of this approach is that each preset represents an 'average' setting that won't necessarily match the specific light conditions in the scene being photographed.
Custom white balance - you set a specific colour temperature in-camera based on the measured or estimated colour temperature in the scene. A simple way to do this is to carry a grey card and photograph it in the ambient light, then use this is a neutral reference point from which to choose an appropriate setting.
There are arguments for and against using all of these options. I know quite a few photographers who use the white balance presets to get them in the ball-park and then make any fine adjustments if necessary later on the computer. I prefer to leave my camera set to auto white balance because it usually does a good job, and it's one less thing I have to think about when I'm out on location. But the auto setting can be tricked, especially if there are mixed light sources or when a scene contains a lot of one colour that the camera misconstrues as a colour cast - I nearly always fine-tune the white balance setting later using software. I don't know of many landscape photographers who use the custom setting with a grey card although I'm sure it can be a useful approach in some situations. But again, it's an extra thing to worry about when on location and it seems to me unnecessary when it is so easy to adjust the white balance later on the computer.
Whichever white balance setting you choose at the time of capture, there is still the option to make further adjustments later in programs like Photoshop or Lightshop if the result isn't to your liking. But there is a catch - if the image was captured as a jpg file then the ability to adjust white balance is limited. Any major adjustment like this to a jpg file comes at the cost of degraded image quality as the pixel data are stretched and manipulated - this is on top of the fact that a jpg file has already been compressed and some of its pixel information discarded. The results can be quite good but some colours may appear a little odd.
A more versatile approach is to capture images as RAW files as these are not compressed in-camera and still contain all of the information recorded by the camera's sensor. The white balance can then be adjusted in RAW converter software (eg. Lightroom, Camera Raw) without degrading the image and with more accurate results. In order to maintain image quality, it is best to make any major changes to white balance in the RAW converter, and then make fine-tuning adjustments in Photoshop or similar imaging software.
RAW converters have a white balance adjustment tool that typically includes two colour sliders and an eye-dropper tool. One slider controls the colour temperature (from blue on the left to yellow/amber on the right) and the other controls green-magenta colour shifts (green on the left, magenta on the right). By manipulating the sliders we can remove any colour casts present in our images, or maybe accentuate or add a colour cast to create a particular mood. One point that confuses many people is that the scale on the colour temperature slider appears to be the wrong way around - bluer colours to the left are assigned a low colour temperature (whereas blue light actually has a high colour temperature) and yellow colours to the right are given a high temperature value (whereas yellowish light has a relatively low colour temperature). What this scale is actually telling us is the colour temperature we need to assign to an image in order compensate for a colour cast. But there's no need to be confused or worried about this - the important thing to note is that pushing the slider to the left makes our images more blue and pushing it to the right makes them more yellow. Our aim is to find a setting that looks right to us, regardless of what the temperature scale says.
The eye-dropper tool can be clicked on any part of an image and it will automatically adjust the two sliders so that the area clicked becomes colour-neutral (grey or white). The trick here is to click on a part of the image that really should be neutral, like the white-water in a waterfall or at the beach, or maybe a grey cloud. Sometimes, a dead tree or a grey rock can make a good reference point, but any of these things can contain a mixture of colours so some judgement is needed before we accept what the eye-dropper tells us. It's a good idea to click on different parts of the neutral reference point before settling on a white balance setting.
The foam line on a beach can provide a neutral target for the eye-dropper tool.
There are times when our image won't contain anything that should be colour-neutral, so there is no obvious place to target with the eye-dropper. This is where it would have been useful to have taken an extra image with a grey card in the frame to use as a neutral reference. Otherwise, it becomes a matter of manually adjusting the sliders until the colours look 'right'.
Imaging software like Photoshop has a wide range of tools that can be used to adjust overall colour balance or to target and adjust specific colours. The colour balance tool is an obvious choice, but curves, levels, selective colour, hue/saturation, photo filters and others can all play a role. Just remember that these tools are relatively destructive to an image and it is better to make major adjustments to the RAW file (if you shoot RAW), or to take extra care with setting the white balance in-camera if you shoot jpgs.
Reading back over this article, I realise I may have given the impression that there is one correct white balance setting for each image and our aim as photographers is to make sure we find this setting. Nothing could be further from the truth. We can go to extreme lengths to ensure that the whites in our images really are white, but that doesn't mean our images will convey the atmosphere we experienced at the time of capture, or even that they will represent the colours of the scene as we saw them. It is important to understand a little of the theory behind white balance and colour temperature and to know how to control them in our images, but this shouldn't stifle our creativity as landscape photographers - there is still plenty of room for artistic interpretation.
Strong colour casts, like those we often witness at sunrise and sunset, are what give images of these scenes life and vitality. If we were to remove the red cast from a vibrant sunrise in order to show white objects as white, we would lose much of the reason for capturing the image in the first place. I can recall a number of particularly colourful sunrises where everything around me was bathed in red light - even my hand held up in front of my face had an eerie red glow. In situations like this, the colour cast is an important part of the moment and the image. The cast could easily be removed on the computer with the white balance tool but that would just produce an image that looked nothing like the scene as we remember it.
The colour balance in every landscape image is open to interpretation by the photographer. A good rule to follow is to never blindly accept what your camera delivers, whichever in-camera white balance setting you use. The image has to look 'right' to you based on your memory of the scene at the time of capture and on the mood you wish to convey in your image. One of the very first tasks I perform when I first open a new RAW file on the computer is to review and adjust the white balance. Sometimes I end up going back to the setting 'as shot' by the camera, but it's always worth moving the sliders around and trying the eye-dropper tool to see how different colour temperatures and tints alter the look of an image.
Many landscape photographers strive to create realistic and believable images that represent what they saw at the time of capture, but there is no rule to say this has to be the case. Take the example of black and white images - these are very popular with some landscape photographers and their audiences for the mood they create, but they certainly aren't an accurate representation of what the photographer saw. So if you play around with the colour balance in your image and find that pushing the colour temperature slider towards the blue end gives you an effect and mood you like, then keep it. It's your image and you get to choose how it looks.