User's Manual

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0
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15.4.9. Overlay Source Color Key Registers
There is an overlay source key per overlay stream, which is used on a pixel basis. The Source
comparison occurs after the horizontal zooming, but in the YUV formats before the color space
conversion. If the source data (overlay) is within the range, then the primary display is selected.
If the overlay is in RGB mode, the most significant bits are duplicated on the least significant to form 8
bit channels:
R<4:0> -> R<4:0 ‘ 4:2>
G<5:0> -> G<5:0 ‘ 5:4>
B<4:0> -> B<4:0 ‘ 4:2>
before the source key comparison is made.
Destination Color Key failing takes precedence over the Source Chroma Key failing. If both fail, then the
primary display is selected.
15.4.9.1. SCLRKVH—Source Color Key Value High Register
Memory Address Offset: 58h (R/W)
On-chip Reg. Mem Addr Offset: 30158h (RO; debug path)
Default Value: 00h
Access: see address offset above
Size: 32 bits
31 24 23 0
Reserved Source Key value High
Bit Description
31:24 Reserved.
23:0 Source Key Value High. This value is the high value that is compared with the overlay pixel per 8 bit
channel. An overlay value greater than this field on any channel that is enabled fails the comparison
and passes the overlay pixel.