pciGrabber-4x4
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PHYTEC Messtechnik GmbH 2008 L-720e_0
6.1.3
Transfer and storage of color
Color and brightness are always separated for the transmission by the
TV-systems. Transmitted are the brightness (luma signal, Y-signal)
and the color differential signal (chroma signal). This signal defines
the color of a pixel by the color tone and color saturation.
The TV-standards reduce the bandwidth of the color signal in
comparison to the brightness signal. The color of a pixel is more
‘blurred’ than its brightness. This corresponds to a painter, who at first
makes a sketch with a sharp pencil and then colors the areas with a
broad brush.
The Y-bandwidth of the PAL (B,G,H,I) - system is 5 MHz, and the
bandwidth of the chroma signal is 1.5 MHz.
The chroma signal is also denoted as U/V signal for PAL standard or
Q/I-signal for the NTSC standard. V- and I-signal define the
reddish colors, whereas the U- and Q-signal define the bluish-violet
colors.
Altogether
we
speak
from
the
Cr/Cb
signal
(chroma red/ chroma blue).
With the triplet (Y,Cr,Cb) the brightness and color of a pixel are
completely defined. These values are ready to be used without further
evaluation for image processing in respect to color recognition or
color control.
Frequently the definition of a pixel is preferred in the red, green and
blue (R,G,B) notation. The transformation according to CCIR-recom-
mendation for PAL is achieved with the following matrix:
⋅
−
−
−
−
=
1
75
,
237
56
,
116
45
,
191
0
698
,
0
371
,
1
732
,
1
338
,
0
0
1
1
1
V
U
Y
B
G
R
