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Barco - RHDM-2301 - User manual 159
Video signal processing
Detailed example: Pure gamma
The OETF shown below describes the translation of the electric signal to the video drive level. This
formula applies for each color.
The light output (luminance) Y
i
for each color (i=R,G,B) of an ideal screen is related to the
maximum light output Y
i
max
(for each color) multiplied by the gamma corrected color factor. The
color factor is the input voltage V
i
in
(or Y
i
’) weighted by the reference white voltage V
i
inrw
. The LCD
screen is not able to suppress all the light coming from the backlight trays. There is still some light
(Y
i
0
) emitted by the LCD screen when V
i
in
= 0. This remnant emission of light is called display black
level. The video gain G is a way to enhance the light output of the image, without influencing the
black level of the image. The gain is expressed in the formula in %. Background B is the user
control that allows the user to shift the black level (e.g. to see the content in dark regions of the
image better) of the image. Picture P is the user control that drives the power of the backlights.
From this equation you can readily see that Picture has an influence on the black level that is set by
the Background and the dark offset of the LCD panel.
, i = R,G,B
NOTE
:
Increasing G or B will result in clipping of the highlights.
γ
⎥
⎦
⎤
⎢
⎣
⎡
+
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−+= B
V
VG
YYYPY
inrw
i
in
i
iiii
100
)(
0max0