28
M = Monitor Response (brightness/mv of camera signal)
For a typical monitor, γ = 2.2; hence the concave, exponential curve if a linear camera signal is
used. To compensate for this, the opposite kind of non-linearity is introduced in the camera,
which modifies the linear characteristic of the CCD as follows:
Camera signal 2
Camera signal 1
Exposure 2
Exposure 1
=×
C
1
γ
C = Camera Response (mv/lux of scene illumination)
The reciprocal of 2.2 is 0.45; if the gamma correction in the camera is set to 0.45, the overall
system response to scene illumination will be linear.
5.9.3 Fixed Gamma Settings in DVC Cameras:
There are three possible settings for Gamma in DVC cameras:
• Gamma = 1.0; This is the default and is ideal for image processing applications ! Most image
processing applications use the linear response of the CCD to measure the relative
brightness of objects within the field of view. After processing, a Look-up-Table may be used
in the Image Processor prior to viewing the processed image on a monitor.
• Gamma = 0.45; This is used when the output of the camera is connected directly to a
monitor, without any image processor. This setting leads to an overall system response that
is linear. However, due to the increased gain in the dark signal regions of the image, it
increases the noise in the image.
• Gamma = 0.6; This is a compromise between a Gamma of 0.45 (with the increased noise)
and Gamma = 1.0 (no correction). The curve tracks the Gamma = 0.45 curve at the higher
signal levels but does not add as much noise in the lower signal area.
5.9.4 Adjustable Gamma Setting in DVC Cameras:
An adjustable Gamma correction is also available; the user can adjust a Gamma control
potentiometer to select Gamma correction from 0.45 to Unity. This is not available on all units;
Call DVC for further information !
To Next Page