HMP8156 Intersil Corporation, HMP8156 Datasheet - Page 4

• Manufacturer Part Number: HMP8156
• Description: Ntsc/pal Encoder
• Manufacturer: Intersil Corporation

Input Processing
COLOR SPACE CONVERSION
For linear RGB input formats, the encoder applies gamma-
correction using a selectable gamma value of 1/2.2 or 1/2.8.
The gamma-corrected RGB data from either the correction
function in linear mode or the input port otherwise is con-
verted to 4:4:4 sampled YCbCr data.
For the YCbCr input formats, the encoder converts the 4:2:2
sampled data to 4:4:4 sampled data. The conversion is done
by 2x upsampling the Cb and Cr data. The upsampling func-
tion uses linear interpolation.
OVERLAY PROCESSING
The HMP8156 accepts overlay data via the OL0-OL2, M0,
and M1 pins. Overlay mixing is done using the 4:4:4 YCbCr
pixel data from the color space converter. The YCbCr data
following overlay processing is used as input data by the
video processing functions.
The OL0-OL2 inputs select the color to be mixed with the
pixel data. Overlay colors 1-7 are standard color bar colors.
Overlay color 0 is special and disables mixing on a pixel by
pixel basis. The overlay color palette is shown in Table 2.
NAME
P10
P11
P12
P13
P14
P15
P16
P17
P18
P19
P20
P21
P22
P23
PIN
P0
P1
P2
P3
P4
P5
P6
P7
P8
P9
Cb0, Cr0
Cb1, Cr1
Cb2, Cr2
Cb3, Cr3
Cb4, Cr4
Cb5, Cr5
Cb6, Cr6
Cb7, Cr7
YCBCR
16-BIT
4:2:2
Y0
Y1
Y2
Y3
Y4
Y5
Y6
Y7
Y0, Cb0, Cr0
Y1, Cb1, Cr1
Y2, Cb2, Cr2
Y3, Cb3, Cr3
Y4, Cb4, Cr4
Y5, Cb5, Cr5
Y6, Cb6, Cr6
Y7, Cb7, Cr7
YCBCR
8-BIT
4:2:2
TABLE 1. PIXEL DATA INPUT FORMATS
HMP8156
OL0
OL1
OL2
Ignored
M0
M1
-
-
-
SAV and EAV
YCbCr Data,
Sequences
4
BT.656
Note that overlay capability is not available when the 24-bit
RGB input format is used.
The encoder provides 4 methods for mixing the overlay data
with the pixel data: disabled, external mixing, internal mixing
and no mixing. The method used is selected in the input for-
mat control register.
Overlay Mixing: Disabled
When overlay mixing is disabled, the OL0-OL2, M0, and M1
inputs are ignored and the pixel data is not changed.
Overlay Mixing: External
When external overlay mixing is selected, mixing of overlay
data and pixel data is controlled by the M1 and M0 inputs.
M1 and M0 indicate the mixing level between the pixel inputs
and the overlay inputs, on a pixel-by-pixel basis. M1 and M0
are ignored if OL2-OL0 = 000. Otherwise, they select the
percentage of each color to sum as shown in Table 3.
OL2-OL0
TABLE 2. OVERLAY COLOR PALETTE
000
001
010
011
100
101
110
111
SCREEN
Ignored
BLUE
(5, 6, 5)
16-BIT
RGB
G0
G1
G2
G3
G4
G5
B0
B1
B2
B3
B4
R0
R1
R2
R3
R4
75% Magenta
100% White
75% Yellow
75% Green
Pixel Data
75% Cyan
75% Blue
75% Red
COLOR
24-BIT
RGB
G0
G1
G2
G3
G4
G5
G6
G7
B0
B1
B2
B3
B4
B5
B6
B7
R0
R1
R2
R3
R4
R5
R6
R7