Computer graphics processing and selective visual display system – Computer graphics display memory system – Frame buffer
Reexamination Certificate
1999-04-22
2002-10-08
Chauhan, Ulka J. (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics display memory system
Frame buffer
C345S632000, C345S215000, C348S569000
Reexamination Certificate
active
06462746
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital video display unit such as a digital television (DTV) and a digital VCR (DVCR) and more particularly to an on screen display (OSD) memory structure in the digital video display unit to produce effects such as superimposition of characters on a picture screen.
2. Description of Related Art
An OSD function is generally used for superimposing images such as graphics and characters on a displayed image of a TV screen. The OSD allows an image selected by a system or a user to be displayed on an original image being displayed using the OSD information stored in a memory unit.
FIG. 1
is a block diagram showing a conventional OSD operation. As shown, when an OSD command, CMD, is transmitted from a host processor
1
to a video processor IC
2
, a video signal decoder
2
a
in the video processor IC
2
decodes the video signals and forwards the decoded signals to an OSD controller
2
b
. The OSD controller
2
b
also receives OSD information from a memory
3
and generates OSD output data. Thereafter, the OSD controller
2
b
displays the images on a display device
4
such as a TV or PC monitor using the video output signals from the video signal decoder
2
a
and the generated OSD output signals.
At early development stages of the OSD operation, only a single OSD region was displayed on a screen. However, with the increase of the demand for more OSD functions, the OSD can now support multiple OSD regions to more effectively use an external memory. As shown in
FIG. 1
, the OSD information is stored in an area of the memory
4
, separate from the video signal. For a single OSD region, the external memory consists one area of both the OSD bitmap information and the command information necessary for display of the bitmap memory. In contrast, for multiple OSD regions, the external memory should include a plurality of bitmap and command areas corresponding to the plurality of bitmap for an implementation of a multistandard OSD.
FIG. 2
a
shows multiple OSD regions displayed on the display device
4
and
FIG. 2
b
shows a memory structure corresponding to the OSD regions shown in
FIG. 2
a
. Referring to
FIG. 2
b
, the OSD region information stored in the command area contains the data designating points of the next region. When the command and bitmap information are stored together, problems may occur while an external host processor updates the OSD information. Particularly, the position onto which a command is written in the OSD region would be variable since a size of a bitmap is variable. Thus, the position of each command must be stored even when the external host processor is updating only the bitmap.
Moreover, when the command and bitmap information are mixed, the host processor for updating the OSD information may not be able to synchronize with the OSD controller for reading the OSD information. In such case, the variable size bitmap tends to intrude into the command area of another OSD, resulting in critical errors in the OSD operation. If the information in the command area is damaged, the host processor writes data onto the memory while outputting the bitmap, thereby affecting the overwriting and resulting in an OSD error.
In the conventional memory, the command area and the bitmap area are not separated in the OSD memory. As a result, the position of the command area is variable and under such condition, synchronization may fail when the host processor updates the OSD information while the OSD controller is reading and processing the OSD information. Thus, an updated new command may be used while the previous data prior to the updated data is used for the bitmap. Furthermore, as discussed above, since the size of the bitmap is variable, the bitmap can be overwritten onto the command area of another OSD when the bitmap is updated.
Due to the large volume of bitmap data, a degree of overwriting the bitmap data may not significantly influence the overall OSD operation. However, for the command data which contains the OSD control information such as the OSD display position, the size and the point of the next bitmap, if the external host processor writes while the OSD controller is reading, a critical error to the overall OSD operation would likely occur.
Highlighting is one function of the OSD operation which simply distinguishes the OSD information from other information by changing a color without changing the content of the OSD information. Generally, such highlighting function has been accomplished using a window based method.
FIG. 3
shows a window based highlighting method designating a start point P
1
and a stop point P
2
to establish the position information of a displayed video, thus setting a window during the operation of displaying the OSD on a screen. The data related to the set window is designated as the command and utilizing such data, the contents of the window are highlighted.
In the window based highlighting method, the position of the set window (start point and stop point) must be noted. Particularly, assuming that 0≦×≦720 and 0≦Y≦480, a minimum of 38 bits comprising 10 bits for X_start, 10 bits for X_stop, 9 bits for Y_start and 9 bits for Y_stop must be stored as part of the information. Accordingly, as the number of different windows to be highlighted increases, the load on the hardware also increases. Furthermore, when one OSD region is displayed on a screen, only the position of the OSD region to be displayed is simply selected and distinguished from the other parts. However, when multiple OSD regions must be displayed, the load on the hardware further increases.
A method to access the color of the highlighted window for the highlighting function will be described with reference to FIG.
4
. Assuming that the index information of a bitmap consists of 8 bits, the color signal data Yn, Cbn and Crn, corresponding to the OSD image, is stored in a color look-up table (CLUT)
12
within the OSD memory and is accessed using the index as an address. The accessed color signal data, Yn, Cbn, and Crn, is visually presented on a screen
14
of the display device.
However, during the actual color access for the portion to be highlighted, the usual OSD CLUT
12
is not used, but a specially generated highlight color look-up table (H-CLUT)
13
is used. After the portion to be highlighted is completely selected and assigned a command, the corresponding color signal data, Yn′, Cbn′, and Cm′ in the H-CLUT
13
is accessed using an index as an address and displayed on the screen
14
, where the index embedded in 8-bit data
11
corresponds to a relevant position in the bitmap area. Consequently, the corresponding OSD region, H
1
, is highlighted. According to this highlight color access method, an additional highlight color look-up table need to be constructed in the hardware, resulting in a heavier load on the hardware.
Generally, the CLUT is referred to for color processing of OSD information when applying the OSD process to an MPEG video in the digital TV or PC. The OSD bitmap stored in the external memory may comprise 2-bit, 4-bit, or 16-bit pixels. When using 8 bits for a pixel, the color look-up table supports 256 colors. The 8-bit data in the OSD memory (bitmap) is used as an index for addressing the color look-up table to read the appropriate color data (address: Addr) from the color look-up table.
Moreover, during the access of the color data in the color look-up table and the OSD processing, a blending process for blending the original video data and OSD data at a proper ratio is performed to implement the various special effects such as a semi-transparent effect on a background of the OSD or the OSD information. To perform this blending process, the blending data indicating at what ratio the original video data and the OSD data are blended is required. For example, if blending effects of 16 stages are wanted, at least 4-bit blending data is needed.
One way to accomplish the OSD blending process is adding the blending data
Bae Seong-Ok
Lee Kyung-Yun
Min Seung-Jai
Birch & Stewart Kolasch & Birch, LLP
Chauhan Ulka J.
LE Electronics Inc.
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