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SDC-10
Operation Guide
Operation Guide Glossary
Gamma Curve
Gamma encoding of images is required to compensate for properties of human vision - to
maximize the use of the bits or bandwidth [in digital devices] relative to how humans
perceive light and color. Human vision under common illumination conditions (not pitch
black or blindingly bright) follows an approximate gamma or power function. If images
are not gamma encoded, they allocate too many bits or too much bandwidth to highlights
that humans cannot differentiate, and too few bits/bandwidth to shadow values that humans
are sensitive to and would require more bits/bandwidth to maintain the same visual quality.
[… excerpt from Wikipedia, 6/11]
The gamma curve of the SDC-15 projector can be custom tailored to match the
relative values of the input signal, the projector’s light output, for optimum picture fidelity.
Adjustments can be made both in total white and via the three primary RGB colors.
The value of the input video image signal is displayed as a percentage - with both being
displayed in % of units - of the maximum light input signal for brightness, and the
brightness output value as a percentage of the maximum output of the projector. We can
say that relative to the signal input value at 50%, it projects with a brightness output value
also at 50%. However, a light output value of 0% is not completely black since that cannot
be projected [the possibility of any projector to reproduce absolute blackness is limited;
thus the light output at “0% black” will be actually slightly brighter in real terms].
The input video image signal value is thus represented by a continuous gamma curve
from 0% to 100%, which can be adjusted by you or your calibrator. The gamma curve
can be set for each color separately, i.e. red, green and blue – or by selecting white to
adjust all colors at the same time.
A larger “angle” of inclination of the gamma curve (“A” below) leads to a greater
differentiation of the light output values in that area, thus making it easier to resolve fine
details in the video. A lower “angle” of inclination will lead to fewer differences in that
area, making the images harder to distinguish between the important gradations (“B”).
If it is impossible to achieve any inclination angle, becoming horizontal, the gap in that
area vanishes and it may be impossible to distinguish between any of the key details
in video (“C”).
Suppose you knew the exact inclination (or gamma curve) value(s) of the input video
signal, and could increase the slope in the desired areas and attenuate the slope in other
portions of the video. The result would be a clearer, well defined image. Conversely, if
one does not know the inclination values of the video content, fine adjustment might be
more difficult to perform. However, there are some known trends of the input signal
value and loosely determined by the type of video content. A few typical examples are
presented in the [Gamma] (Reference Page:48).
Some methods about how to adjust the gamma curve are presented here, but in reality
one can think of various adjustment methods, for example where red, green and blue
are individually adjusted. In your own image creation, please work the process of trial
and error and discover for yourself the impact of various gamma curves.
0%
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Summary of Contents for SDC-10
Page 1: ...SDC 10 ...
