Sony NEX-EA50 NXCAM Handbook page 41

Gamma Curve and Knee Point
Gamma curve and knee point are two elements that exert great influence over image characteristics. By understanding these, you'll
be able to utilize PICTURE PROFILE efficiently.
What is a gamma curve?
Gamma curves show the relationship between the input signal
level and the output signal level. The camera converts the
brightness signal from the subject into an electrical signal
and sends the electrical signal to the display monitor, which
converts that signal back to a brightness signal and reproduces
the subject as an image.
The input signal level is the amount of the brightness signals
from the subject and the original image overall, whereas the
output signal level is the amount of the brightness signal
output by the camera or display monitor.
In order to faithfully reproduce a subject in video images, the
output signal level needs to be largely proportional to the
input signal level, as shown in the straight line below. But
the fluorescent material characteristics of a CRT (cathode-
ray tube) cause the output signal level from CRT monitors to
curve as shown below. This represents the gamma curve of
CRT monitors (red curved line). Video cameras' gamma curve
(blue curved line) plots the opposite curve. For this reason,
the properties of the camera and CRT monitor can be offset to
faithfully reproduce and display the original subject.
Nowadays, display monitors based on LCD, plasma and OLED
are used widely. Because these monitors have different gamma
curve characteristics from those of CRT display monitors, the
ITU has set the gamma value for display monitors that are used
in broadcasting and video production at 2.4 (ITU-R BT1886).
This value was decided by taking into account that the gamma
How a gamma curve's shape influences images
Influence on dark areas and contrast
High-end camcorders have a function to slightly change the shape of the gamma curve for dark areas of the image. Known as black
gamma, this function lets you dramatically alter the atmosphere of the image by changing the gamma curve shape and strengthening
or weakening the shading, or image contrast, of the image.
value of actual CRT master monitors used in broadcasting and
video production was closer to 2.4, rather than their theoretical
value of 2.2.
Sony's LCD and OLED display monitors enable users to choose
a gamma curve that simulates that of conventional CRT
monitors for smoother continuity from old systems.
100%
Video Gamma
= 1/2.2 = 0.45
Output
39 39
CRT Gamma
= 2.2
Input 100%