Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1998-02-19
2001-07-03
Lee, Michael H. (Department: 2714)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
C348S556000
Reexamination Certificate
active
06256045
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a picture decoding, and more particularly, to device and method for processing a picture in an MPEG decoder which can reduce an amount of data to be stored in a memory.
2. Discussion of the Related Art
The techniques of video compression and multiplexing in the Grand Alliance system, which is the HDTV (High Definition TV) system of the U.S., follow the MPEG (Moving Picture Experts Group)-2 standards as they are. The standards for video format do not restrict to one video format, but allows different video formats in encoding and decoding. For example, there are a format with a 60 Hz field rate for a video source of 1080(V)* 1920(H) interlace scanning and formats with 24 Hz and 30 Hz frame rates for a video source of 720(V)* 1280(H) progressive scanning in the HDTV class, and there are formats with 24 Hz, 30 Hz and 60 Hz frame rates for a video source of 480(V)*720(H) interlace scanning and formats with 24 Hz, 30 Hz and 60 Hz frame rates for a video source of 480(V)*640(H) progressive scanning in the SDTV (NTSC) class. The HDTV class has an aspect ratio of 16:9 and the SDTV class have an aspect ratio of 16:9 or 4:3. Thus, though there are different video formats possible to receive, video formats possible to be displayed on a monitor, such as a TV receiver, will be in general limited to one or two to be consistent to the monitor feature, despite such a monitor can receive and display any video formats. Further, even if the HDTV broadcasting is started, since it is foreseen that the HDTV broadcasting and current NTSC or SDTV broadcasting coexist for a substantial period of time, it is required that they have to have an interchangeability. That is, if a monitor has a display standard of an SD class while a video source has an HD class, a video format conversion from the HD class to the SD class will be required. Similarly, a video format conversion of a video with an aspect ratio of 16:9 for display on a monitor with an aspect ratio of 4:3 will also be required, and vice versa. Thus, if a display format, i.e., a display size and a video source size are different from each other, a video format conversion is required.
A system of a background art MPEG decoder for conducting this is illustrated in
FIG. 1
, wherein the MPEG decoder
10
in general uses an external memory
20
provided with a buffer for temporary storage of a bit stream and a frame memory. The MPEG decoder
10
is provided with an interfacing part
11
for interfacing an encoded bit stream with the external memory
20
, a memory controlling part
12
for controlling data input/output from/to the external memory
20
and the MPEG decoder
10
, a video decoder
13
for decoding the bit stream stored in the external memory
20
and storing decoded pixel data in the external memory
20
, and a video presenting part
14
for processing a signal of the pixel data stored in the external memory such that the pixel data is displayable on a display
30
and converting a format of a video source if formats of the video source and the display
30
are different from each other.
FIG. 2
illustrates an operation flow chart of the MPEG decoder
10
shown in FIG.
1
.
Referring to
FIGS. 1 and 2
, when an encoded bit stream is transmitted and received at the MPEG decoder
10
, the bit stream is stored in the external memory
20
through the interfacing part
11
. Then, the video decoding part
13
reads the bit stream from the external memory, decodes (step
201
), and stores the bit stream in the external memory
20
, again (step
202
). That is, the video decoding part
13
removes overheads (various header information, start codes and etc.) from the received bit stream and conducts a VLD (Variable Length Decoding) of pure data information to restore the bit stream into pixels of an original image through an inverse quantizing process, inverse discrete cosine transformation (IDCT) and motion vector using motion compensation process. In this instance, all data input/output from/to the external memory
20
and the MPEG decoder
10
are conducted under the control of the memory controlling part
12
. The external memory
20
is required for writing and reading of the bit stream for variable length decoding, data reading for motion compensation, and writing a decoded data and reading a data to be displayed, and because an order (I, P, B, B) of pictures to be decoded and an order (I, B, B, P) of pictures to be displayed are different. The image presenting part
14
reads the pixel data of a picture, decoded in the video decoding part
13
and stored in the external memory
20
, in an order of display, processes signals to be displayable on a screen (step
203
), converts a video format if the video source and display
30
are different in numbers of display pixels, data transmission rates, or aspect ratios, and presents to the display
30
. That is, the image presenting part
14
determines a display size and a video source size of being different from each other after processing the signal (step
204
). The size herein may denote a number of pixels, an aspect ratio of the image, or a data transmission rate, called a frame rate. It the display size and the source size are determined to be identical in the step
204
, the data signal processed are presented to, and displayed on the display
30
without any conversion of video format (step
205
). On the other hand, if determined different in the step
204
, the display size is compared to the video source size whether the display size is greater or smaller than the video source size (step
206
). If it is determined that the display size is greater than the video source size in the step
206
, for example, the display has an aspect ratio of 16:9 while the video source has an aspect ratio of 4:3, or the display is an HD class while the video source is an SD class, the decoded I, P, B pictures are subjected to operations such as pixel interpolations respectively and present to the display
30
(step
207
). If determined that the display size is smaller than the video source size in the step
206
, that is, it is opposite to the step
207
, the decoded I, P, B pictures are subjected to data reduction operations such as pixel filtering respectively and present to the display
30
(step
208
). As there are many known video format converting techniques, some of the techniques may be used.
FIG. 3
illustrates one of the video format converting technique, wherein a letter box processing is made, in which a video signal with a 16:9 aspect ratio is converted into a video signal with 4:3 aspect ratio. In the method of converting a video signal with a 16:9 aspect ratio is converted into a video signal with 4:3 aspect ratio, there are, other than the letter box processing, the pan scan method in which opposite sides of a decoded data are cut away to make an aspect ratio of 4:3 or a method in which a 16:9 image is compressed in a horizontal direction to convert it into an aspect ratio of 4:3.
FIG. 4
illustrates an example of a letter box filtering for preventing an image from being distorted when an image of 16:9 aspect ratio is displayed on a TV of 4:3 aspect ratio, in which 3 scan lines are presented per every 4 samples. That is, in the letter box filtering, an upper and a lower pixels in a frame is interpolated to adjust a number of the pixels; pixels in a vertical direction in a frame are interpolated, to call it as a vertical filtering. This vertical filtering leads a number of pixels reduced to ¾ compared to a number of pixels in a frame of an original image. Therefore, in the case of letter box processing, a rate of data transmitted from the image presenting part
14
to the display
30
is reduced to ¾ compared to a rate of data transmitted from the video decoding part
13
to the image presenting part
14
through the external memory
30
. In this instance, the filtering coefficients shown in
FIG. 4
may be different depending on methods of implementation. Thus, in the background art, a
Bae Sung Ok
Min Seong Jae
Fleshner & Kim LLP
Lee Michael H.
LG Electronics Inc.
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