Consider the idea that the camera is without a brain – when converting light signals into electricity, it does so on an entirely mechanical level, without any subconscious or set pattern in mind. The human brain, on the other hand, filters sensory information such as light perception with automatic additions and adjustments on such a natural level that we don’t even know it is happening.
The difference between the human eye and the camera lens is evident when changing from one type of light to another. When shifting between synthetic indoor lights and the natural hue of daylight, the human eye recognises the difference and quickly adjusts to the change in conditions (this adjustment is barely noticeable to us humans). A camera in this situation, however, will not handle things quite as well. It may be initially calibrated to interpret conditions for indoor lighting accurately, but when shifting to natural outdoor light an incorrect perception of colour will result with the camera presenting an image that is overly blue.
When thinking of this in film terms, the colour balance may need to be corrected while shooting or printing to achieve a neutral colour print. This is where the ‘white board’ step comes into play – by placing a plain white sheet in front of a camera before filming, it can then recognise that ‘version’ to be the ‘natural’ white. It then adjusts its perception of other colours based on that starting point, allowing the camera to avoid any colour disorientation.
In terms of film and video, the term ‘colour temperature’ refers to the range of light sources available to be filmed, measured traditionally using the ‘Kelvin Scale’. For instance, one of the ‘hotter’ light sources - blue skylight, is measured between 9500-20,000k. When compared to something smaller such as a match flame, which measures around 1700k, one can easily see the vast differences available concerning colour temperature and the fidelity in which a camera reproduces light.
|Comparison between varying degrees of colour temperature|