865G Datasheet, PDF (173/249 Pages) Intel Corporation – Intel 865G/865GV Graphics and Memory Controller Hub

Functional Description
5.4.4.2
Overlay Plane
The overlay engine provides a method of merging either video capture data (from an external video
capture device) or data delivered by the processor, with the graphics data on the screen. The source
data can be mirrored horizontally, vertically, or both.
Source/Destination Color Keying/ChromaKeying
Overlay source/destination ChromaKeying enables blending of the overlay with the underlying
graphics background. Destination color keying/ChromaKeying can be used to handle occluded
portions of the overlay window on a pixel by pixel basis that is actually an underlay. Destination
ChromaKeying would only be used for YUV passthrough to TV. Destination color keying supports
a specific color (8- or 15-bit) mode as well as 32-bit alpha blending.
Source color keying/ChromaKeying is used to handle transparency based on the overlay window
on a pixel-by-pixel basis. This is used when “blue screening” an image to overlay the image on a
new background later.
Gamma Correction
To compensate for overlay color intensity loss due to the non-linear response between display
devices, the overlay engine supports independent gamma correction. This allows the overlay data
to be converted to linear data or corrected for the display device when not blending.
YUV-to-RGB Conversion
The format conversion can be bypassed in the case of RGB source data. The format conversion
assumes that the YUV data is input in the 4:4:4 format and uses the full range scale.
Maximum Resolution and Frequency
The maximum frequency supported by the overlay logic is 170 MHz. The maximum resolution is
dependent on a number of variables.
Deinterlacing Support
For display on a progressive computer monitor, interlaced data that has been formatted for display
on interlaced monitors (TV), needs to be de-interlaced. The simple approaches to de-interlacing
create unwanted display artifacts. More advanced de-interlacing techniques have a large cost
associated with them. The compromise solution is to provide a low cost but effective solution and
enable both hardware and software based external solutions. Software based solutions are enabled
through a high bandwidth transfer to system memory and back.
Dynamic Bob and Weave. Interlaced data that originates from a video camera creates two fields
that are temporally offset by 1/60 of a second. There are several schemes to deinterlace the video
stream: line replication, vertical filtering, field merging, and vertical temporal filtering. Field
merging takes lines from the previous field and inserts them into the current field to construct the
frame – this is known as Weaving. This is the best solution for images with little motion; however,
showing a frame that consists of the two fields will have serration or feathering of moving edges
when there is motion in the scene. Vertical filtering or “Bob” interpolates adjacent lines rather
replicating the nearest neighbor. This is the best solution for images with motion; however, it will
have reduced spatial resolution in areas that have no motion and introduces jaggies. In absence of
any other deinterlacing, these form the baseline and are supported by the GMCH.
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Intel^® 82865G/82865GV GMCH Datasheet