Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1998-05-13
2002-08-27
Hjerpe, Richard (Department: 2774)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C348S441000
Reexamination Certificate
active
06441813
ABSTRACT:
BACKGROUND OF THE INVENTION
This application is based on Japanese Patent Application No. 9-127398, filed on May 16, 1997, and Japanese Patent Application No. 9-127399, filed on May 16, 1998, the content of which are cited herein by reference.
The present invention relates to a computer system and a video decoder, and more particularly to a computer system having a function of decoding digital compressed codes of motion-picture data and displaying the motion-picture data on a display monitor of a noninterlace display system, and a video decoder used in the system.
With the recent development in the field of computers and multimedia technology, more and more computers capable of executing multimedia applications are developed. The computers of this type have a function of reproducing not only text and graphics data but also motion pictures and sound data.
In accordance with an increase in the number of multimedia computers, DVDs are attracting the attention of those skilled in the art, as a new type of storage media replacing CD-ROMs. About 4.7 GB of data, which is about seven times greater in amount than the data recorded on a traditional CD-ROM, can be recorded on one side of a DVD-ROM, and about 9.4 GB of data can be recorded on two sides of the DVD-ROM. The use of the DVD-ROM enables movie titles, which contain a large amount of video information, to be reproduced on a computer screen with high quality.
Video information stored on a DVD-ROM is made up of two kinds of data: presentation data and navigation data. The presentation data is data on video objects to be reproduced, and includes video, sub-picture and audio data. The video data is 1 and compressed according to MPEG-2, while the sub-picture and the audio data are compressed according to run-length encoding or Dolby digital system. The sub-picture data is bit-map data, and used to represent movie titles or display a number of choice items on a menu screen. One video object can include video data of one channel, audio data of up to 8 channels, and sub-picture data of up to 32 channels.
The navigation data is reproduction control data used for controlling the order in which presentation data are reproduced, and navigation commands can be embedded in the navigation data. The navigation commands are used for changing the contents of video data to be reproduced and the order in which they are reproduced. By using the navigation commands, the person who prepares the movie titles can define various tree structures in them, so as to make the movie titles interactive.
The titles are prepared on the assumption that they will be reproduced on a home TV by use of a commercially-available player. The contents of the titles are the following two:
(1) frame data (progressive data) which is encoded at a frame rate of 24 Hz, like a movie film; and
(2) field data which is encoded at a rate of 60 Hz (i.e., the number of field data pieces used per second is 60).
Some of the titles are a combination of data (1) and (2) above. For example, a program is constituted by data (1), namely, frame data (progressive data), while CM information is constituted by field data.
Both the frame data (progressive data) and the field data (data [1] and data [2]) are decoded by a DVD decoder. This DVD decoder outputs 60 Hz field data for interlace display corresponding to an NTSC output. In order to display the field data on the display monitor of a computer, the data for interlace display output from the DVD decoder has to be converted into data for noninterlace display. This conversion is executed by use of simple field synthesis. That is, an even-numbered field and an odd-numbered field are synthesized in a frame memory to produce one frame, and this frame is shown on the display monitor of a computer in a noninterlace fashion.
According to the interlace
oninterlace conversion based on the single field synthesis, fields between which a time difference exists are synthesized into one frame. This results in a so-called “feathering” phenomenon, wherein the outline of the frame appears to. have a fringe. This phenomenon is marked particularly in the case of a quick motion scene.
The “feathering” phenomenon is attributable to the following two causes:
(i) Field Picture Problem
This problem is due to the synthesis of field data (data [2]). Since each field picture corresponds to a time difference of 1/60 seconds, synthesis of them inevitably produces “feathering”.
(ii) Repeat Field Problem:
When a DVD decoder decodes frame data (progressive data) of 24 frames/sec, it uses a method called “3:2 pulldown”. By this method, frame data of 24 frames/sec is converted into field data of 60 fields/sec. The “3:2 pulldown” method is shown in FIG.
11
.
Referring to
FIG. 11
, “Frame No.” indicates the frame number of frame data (24 frames/sec) which is not yet decoded. “Field No.” indicates the field number of field data (60 fields/sec) which is already decoded and corresponds to NTSC. The suffix letter “E” of the field number indicates that the field is even-numbered, while the suffix letter “O” indicates that the field is odd-numbered.
In the “3:2 pulldown” method, the difference in frame rate is dealt with by preparing three fields from one frame, and two of three frames are used in the processing for preparing three fields. When three fields are prepared, the third field is the same data as the first field (R: a repeat field). In
FIG. 11
, the third field of the first frame is a repetition of the first field (
1
E), and the third field of the third frame is also a repetition of the first field (
3
O).
In the simple field synthesis processing, consecutive two field pictures (namely,
1
E and
1
O,
1
E and
2
O,
2
E and
3
O, . . . ) are synthesized together, as shown in FIG.
11
. What becomes a problem at the time of synthesis is the combination between fields
1
E and
2
O and the combination between fields
2
E and
3
O. Fields
1
E and
2
O are prepared from data of different frame numbers, and there is a time difference of 1/24 seconds between fields
1
E and
2
O. Likewise, there is a time difference of 1/24 seconds between fields
2
E and
3
O. As can be seen from this, a frame produced by a combination of fields that includes a repeat field causes “feathering.”
As described above, if titles prepared for a TV are displayed on a display monitor of noninterlace display system, the field picture problem and repeat field problem described above occur, resulting in “feathering”. In particular, where titles are prepared from frame data that must be processed in the “3:2 pulldown” method, half of the field combinations includes fields between which a time difference exists. In comparison with the quick motion picture shown on a TV, the quick motion picture shown on a display monitor of noninterlace display system is poor in quality.
BRIEF SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a computer system and a video decoder that enable a “feathering”—free smooth image to be displayed on the display monitor of a computer by preventing fields between which a time difference exists from being synthesized or combined.
Another object of the present invention is to provide a computer system and a video decoder that enable a “feathering”—free smooth image to be displayed on the display monitor of a computer by means of a simple hardware structure capable of excluding repeat fields from the fields to be combined.
To achieve these objects, the present invention provides a computer system which is provided with a decoder for decoding a video data stream that is in the form of digital compressed codes, which converts video data output from the decoder and adapted for interlace display into video data suitable for noninterlace display, and which displays the resultant video data on a display monitor, the computer system comprising: conversion means for converting the video data adapted for interlace display into the video data suitable for noninterlace display in one of two conversion modes including a field
Eisen Alexander
Hjerpe Richard
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