82845G Datasheet, PDF (129/193 Pages) Intel Corporation – Intel 82845G/82845GL/82845GV Graphics and Memory Controller Hub (GMCH)

Functional Description
4.4.2.4
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 or vertically or both.
Source/Destination Color Keying/Chromakeying
Overlay source/destination chromakeying enables blending of the overlay with the underlying
graphics background. Destination color/chromakeying can be used to handle occluded portions of
the overlay window on a pixel by pixel basis that is actually an underlay. Destination color keying
supports a specific color (8- or 15-bit) mode as well as 32-bit alpha blending.
Source color/chroma keying 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 is to provide low cost but effective solutions and enable
both hardware and software based external solutions. Software-based solutions are enabled through
a high bandwidth transfer to system memory and back.
Intel^® 82845G/82845GL/82845GV GMCH Datasheet
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