845GL datasheet(129/193 Pages) INTEL

129 / 193 page

Intel® 82845G/82845GL/82845GV GMCH Datasheet

129

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.

845GL Datasheet(PDF) 129 Page - Intel Corporation