PRODUCT SPECIFICATION
TMC22091/TMC22191
Color Lookup Table
The CLUT can be used in a variety of ways, depending on
the data format and source presented to the PD port.
gamma correction, are easily loaded. The color data is
loaded into the tables in G-B-R sequence in GBR mode, and
R-G-B sequence in RGB mode.
The CLUT is loaded like a RAMDAC, sequentially writing
one byte to each of the three locations associated with the
selected CLUT address. These three locations are referred to
as Tables D, E, and F as shown in table 16 (not R,G, and B
because they may or may not contain RGB information). and
are loaded in that sequence. The address will increment auto-
matically after the three values at one address are written or
read.
Luminance/Color Difference Modes
The TMC22x91 expects Y, B-Y, and R-Y signals at the input
to its modulator section. When presenting CCIR-601YC C
or digitizedY, B-Y, R-Y data to the CLUT, gain and offset fac-
tors are needed. Table 4 specifies the recommended transfer
B R
functions. The CLUT is loaded inY-C -C sequence.
B
R
Overlay Operation
For the TMC22091 and TMC22191 (when Format Control
Color-index Modes
In color-index (CI) mode, the CLUT is used to store the
color look-up data, translating the 8-bit source pixel data into
24-bit RGB colors. Table D holds red data, Table E is green
data, and Table F holds blue Data. The incoming data are
presented to the three tables in parallel, and a 24-bit output is
produced.
Register Bit 6 = LOW), the OL inputs are inactive. In
4-0
CCIR-601 operation, the nominal data range forY is from 16
to 235 and for C and C is from 16 to 240. This means that
B
R
CLUT locations 0 to 15 and 241 to 255 are available for
overlay colors. When the overlay locations are addressed (by
forcing CLUT addresses outside the normal CCIR-601 data
range), the addressed CLUT data is encoded resulting in the
specific color found in that CLUT location. Overlay colors
information stored in the unused CLUT locations must be Y,
B-Y, R-Y values. Y, B-Y, and R-Y values are found from
RGB values by:
When the encoder is connected in parallel with a RAMDAC
in a VGA system, the CLUT can be loaded simultaneously
with the CLUT in the output RAMDAC. If a 6-bit RAMDAC
is employed, 6 bits can be loaded via data pins D (MSB
7-2
justified). The two LSBs should be set to 00 for optimal
black level representation, but the largest error introduced by
extraneous data in the LSBs is 3/4 LSB (at 6 bits). The
encoder will produce the closest possible translation of the
VGA colors in the encoded video environment.
Y = 0.299 R + 0.587 G + 0.114 B
B-Y = -0.299 R – 0.587 G + 0.886 B
R-Y = 0.701 R – 0.587 G – 0.114 B
For the TMC22191, when the Format Control Register
GBR/RGB Modes
Bit 6 = HIGH, Overlay is controlled by the OL inputs
4-0
The nominal configuration for GBR/RGB modes is unity
gain (CLUT data = CLUT address) for PAL and NTSC.
Other transfer functions, such as gain adjustment, offset, and
which directly access CLUT locations, 01 thru 0F and F1
thru FF, as shown in Table 5. The values stored in these
CLUT locations must be in RGB format.
Table 4. CLUT Transfer Functions for NTSC and PAL
Input Format (CLUT Address)
Output Format (CLUT Data)
Component
Data Range
0 to 255
0 to 255
0 to 255
16 to 235
±112
Transfer Equations
R =R
Component
Data Range
0 to 255
0 to 255
0 to 255
0 to 255
±113
R
G
B
Y
R
O
0
G =G
0
G
O
O
B =B
0
B
Y = Y * 1.1644 – 18.63
O
Y
O
C
B
C
R
(B-Y) = C * 1.0126
(B-Y)
(R-Y)
O
B
O
±112
(R-Y) = C * 0.8011
±90
O
R
O
Y
0 to 255
±127
Y =Y
Y
0 to 255
±113
0
O
B-Y
R-Y
(B-Y) = (B-Y) * 0.893
(B-Y)
O
O
±127
(R-Y) = (R-Y) * 0.7065
(R-Y)
±90
O
O
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