Apple Aperture Digital Photography Fundamentals - Manual (Page 28)

28 Chapter 2 How Digital Images Are Displayed
The subjective nature of visual perception should not necessarily be viewed as a
handicap. If anything, it may be a blessing. Many challenges in photography come
from the fact that the technology is so unforgivingly objective. A common example of
this is the issue of white balance. Both film stocks and digital image sensors are
designed to interpret white under specific conditions. Outdoor light (daylight)
contains a lot more blue light than indoor (incandescent) light bulbs and candlelight.
White objects in these different lighting conditions objectively look more blue
(daylight), more red (incandescent), or more green (fluorescent), but the brain uses a
number of psychological clues to infer that white objects are white, even if they are
objectively different.
A white car during sunset objectively looks quite orange, but if someone asks you what
color the car is, you would reply with certainty that the car is white. That’s because you
know the car is white even if it doesn’t look white at the moment. In the morning, the
car has a bluish tint, and yet again, you would simply say it is white. Digital image
sensors and film, on the other hand, record only what they objectively receive, and
don’t interpret it. The auto white balance feature on many digital cameras measures the
scene in the viewfinder and tells the camera to interpret the brightest point as white.
This is important to know when switching between different lighting scenarios.
Light and color can be objectively measured and characterized. The scientific analysis
of light and color is necessary to build reliable, consistent photographic tools such as
film, digital image sensors, displays, and printers. The goal is not necessarily to make
all these devices capture or display colors the same way (although this would make
things a lot easier), but to develop terminology and processes to objectively measure
how these devices are different and adjust output accordingly, so that results match
visual perception.