The white balance control determines how colour is recorded, while the ISO control sets the sensor’s sensitivity to light.
White balance
The white balance control works by removing the unrealistic colour casts produced by different kinds of lighting. It is configured to ensure the white objects in a scene appear white in your photos; hence the term ‘white balance’.
Your smartphone camera usually relies on a non-adjustable Auto white balance setting, which should produce acceptable results for indoor shots under artificial lighting, like the one shown here.
Smartphone cameras generally rely on automatic detection and compensation. So do most regular cameras, and in most kinds of lighting they work well. Additional adjustments are provided because, while our eyes can compensate for colour casts from different light sources, few cameras are equally capable.
Although they’re less common these days, incandescent (‘tungsten’) lights produce a warm orange cast that can be difficult for camera processors to remove. Fluorescent lights are more variable as they come in ‘warm’, ‘cool’ and ‘daylight’ versions that can create slight blue, orange or even green casts.
The Auto white balance setting should remove most colour casts produced by fluorescent lights, regardless of their colour balance. It should also be able to produce natural-looking whites under modern LED lighting, although some cameras may struggle with warm-toned LEDs.
Natural lighting normally delivers good results with your camera’s white balance setting, as shown in the top picture. In such cases, you’ll probably find the White Priority setting (middle picture) removes the warm cast of the morning light that is integral to the image’s appeal. Judge for yourself whether the Keep Warm Tones setting (lowest picture) added too much warmth or actually enhanced the existing effect.
Many cameras provide several Auto white balance settings. One is the regular Auto mode, while the others are White Priority, which adjusts the auto setting to make white areas noticeably whiter, and Keep Warm Tones (or ‘Ambience Priority’), which preserves the original warm tones of the lighting. You might want to use that setting when taking photos indoors to enhance a warm atmosphere.
Most cameras also have a range of pre-sets that match situations in which the processor may not deliver optimal compensation. Unfortunately, these settings often over-compensate, so they should be used judiciously.
A typical manual white balance adjustment screen. In this case, the white dot in the top left segment indicates the photographer has shifted the colour balance by two steps towards green and one step towards blue. This would have a slight ‘cooling’ effect on the overall colour balance.
Manual adjustments are usually provided for fine-tuning colour corrections, like the example shown on this page, which has two axes: magenta-green and blue-amber. You move the white dot to shift the colour balance in the direction you choose.
You can also make a ‘Custom’ measurement of the colour balance by photographing a white card under the light source in question. In challenging conditions, this can be a useful last resort.
Note: Some subjects create problems, even in normal daylight. When you’re photographing people or objects in open shade you might find a slight blue-green cast. Similarly, close-ups of warm-toned objects, such as autumn leaves can occasionally be over-corrected and may end up slightly bluish.
Mixed lighting is common in situations where daylight streams into an area that is mainly lit with artificial lighting, as shown in this shot taken with the camera’s default Auto white balance setting. Most people would accept this rendition as natural looking so there would be no need to adjust the white balance.
Scenes in which there is a combination of natural and artificial light, as shown on this page, may also produce disconcerting results because the auto white balance averages out all the colours in the scene. Sometimes this works; sometimes not. When it doesn’t, you’ll probably need to decide which of the lighting options to prioritise. That’s also where manual adjustments can really help.
In general, for most situations you can leave your camera on the Auto white balance setting. However, you may prefer using the White Priority mode in some indoor situations – unless you want to keep the warm colours produced by the room’s normal light source.
ISO sensitivity
ISO adjustments are like the volume control on an amplifier: turn the knob up enough to do the job – but not so far it distorts the sound. Only instead of adjusting sound levels, the ISO control adjusts the gain (sensitivity) of the image sensor.
To use this control effectively, it helps to understand your camera’s ISO menu. The standard ISO range adjustments vary in one-stop increments, which double or halve the value, depending on whether it’s up or down. Going from ISO 100 to ISO 200 doubles the sensor’s sensitivity, while going from ISO 800 to ISO 400 halves it.
These ISO menu pages from a typical camera show the range of adjustments available. The box outlined in red in the top left panel indicates the camera has been set for Auto ISO control with an upper limit of ISO 51200 for both normal and flash exposures. Shutter speed settings are determined by the camera’s image processor.
Most cameras’ menus provide customisable Auto ISO settings that let you specify the upper and lower limits of the usable ISO range. Many also let you define the slowest tolerable shutter speed for the sensitivity range, which can be useful if your camera and/or lens is not stabilised. (We look at stabilisation in the next chapter.)
The background image was taken in very dim lighting with the camera hand-held. Because flash was not used, it required a high ISO 12800 setting with a shutter speed of 1/40 second. The inset shows some of the noise-reduction processing settings available when the image is being edited.
Image noise is an inevitable part of all electronic/digital signals. It’s produced by a combination of the randomness of the photons of light, data processing disturbances and the effects of heat and amplification on the digital signal. Some background noise is always present in any device that transmits or receives a digital signal.
In most cameras, the relationship between ISO and image noise is predictable – and fairly linear. Using the ISO control effectively involves balancing the gain against the image noise produced when you ramp the ISO up.
All cameras have a default base level of between ISO 100 and ISO 200, where the manufacturer knows image noise is at its lowest. This setting should be used whenever possible.
Up to a certain point, increasing sensitivity above the base level doesn’t have much effect on how much noise you can see (visible noise). Beyond that point – usually from around ISO 6400 – it becomes evident (although you may not notice it until the image is displayed on a large screen).
The top image was recorded with an extremely high sensitivity. Below it is a crop from a small section from the centre of the frame, enlarged to show the granularity resulting from image noise.
In modern cameras, noise-reduction (NR) processing is automatically applied to all JPEG files so most cameras should be good at keeping visible image noise under control when you dial up the ISO. Older smartphones and smaller compact cameras may struggle with noise due to their tiny image sensors, but most should be capable of producing images with barely visible noise at ISO 3200, thanks to NR processing.
Newer smartphone cameras use sophisticated AI-based NR processing to produce usable images in very low light levels. However, you don’t get much control over how it’s applied and it usually takes several seconds to process a typical low-light photo.
Noise-reduction processing has been refined significantly in recent smartphones and will probably find its way into up-coming cameras. These two snapshots from different smartphone cameras show just how effectively images from very small sensors can be made to perform at high ISO levels. The top picture is a 1/10 second exposure at ISO 640, while the bottom picture is a 1/25 second exposure at ISO 3226. Both shots took a couple of seconds to process.
Useful links
This article by Margaret Brown is an excerpt from Take Better Photos pocket guide – click here to order print or ebook edition.
Pocket guide Partner: Camera House
