Submitted version of the thesis - Airlab, the Artificial Intelligence ...

5.2. Color Definition 61
Anotherautomaticadjustmentcanbedoneonexposure. Subjectslighter
than middle gray, such as a white china plate, reflect more than 18% of the
light falling on them. The exposure system doesn’t know that the scene
should look bright, so it calculates an exposure that produces a middle gray
image that is too dark. Subjects that are darker than middle gray such as
black cloth, reflect less than 18% of the light falling on them. The exposure
system calculates an exposure that makes the image middle gray and too
light.
The contrast or difference in brightness between the subject and the
background can fool an exposure system, particularly if the subject occupies
a relatively small part of the scene compared to the background. The
brightness of the background is so predominant that the automatic exposure
systemadjuststheexposuretorendertheoverall brightnessasamiddlegray.
If the main subject is lighter than the background, it will be overexposed
and too light. If it’s darker than the background, it will be underexposed
and too dark.
Depending on the arrangement of the lighting, some subjects may be
too contrasty with brightly lit highlights and deep shadows. The range of
brightness may exceed the range that can be captured by the camera. In
these cases adjustments should be made in the lights to balance out the
light and to lower the contrast. However, deciding whether the highlight or
shadow areas are most important for the final picture, the exposure setting
should be made appropriately.
The perfect exposure retains details in both the highlights and shadows.
For the auto exposure system, this is as difficult. If there is even a little too
much exposure, the image is too light and details are lost in the highlights.
If there is too little exposure, the image is too dark and details are lost in
the shadows.
When confronted with any subject lighter or darker than middle gray,
exposure compensation is used to lighten or darken the photograph that the
camera would otherwise produce.
To lighten a picture, the exposure is increased. This is useful for setups
wherethebackgroundis muchlighter than thesubject, or whenphotographing
very light objects, such as white china on a white tablecloth. To darken
an image, the exposure is decreased. This is useful for setups where the