Television – Nonpictorial data packet in television format – Including teletext decoder or display
Reexamination Certificate
1997-05-29
2001-03-20
Lee, Michael (Department: 2614)
Television
Nonpictorial data packet in television format
Including teletext decoder or display
C348S461000, C386S349000
Reexamination Certificate
active
06204883
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a video subtitle data encoder and decoder suitable for use in transmitting subtitle data together with video data so that subtitle information may be displayed in a superimposed manner on a video image with reduced degradation of video image quality.
BACKGROUND OF THE INVENTION
Typically, when one watches, for example, a foreign movie, a textual subtitle is often superimposed on the display screen along with video imagery. In video disks or ordinary TV broadcasting, video signals are transmitted in a state in which subtitles have been superimposed beforehand on the video images. In currently known systems, such as CAPTAIN and CD-G, subtitles may be transmitted as character codes or dot patterns.
CD-G is adapted to be able to record graphics utilizing subcodes and utilizing that, it is also possible to record subtitles in a CD. In the CD-G, one frame of data is composed of one byte subcode and 32 byte data, as shown in FIG.
22
. In the 32 byte data, six samples of two byte data per sample are allocated to L and R channels, respectively. Accordingly, the total is 24 bytes. Then, an eight byte error correction code is added to the 24 byte audio data, resulting in the data of 32 bytes in total.
On the other hand, 98 frames of subcodes are assembled to compose one block. Among the 98 frames of subcodes, the first two frames of subcodes are allocated for sync patterns S
0
and S
1
. Various subcode data may be recorded in the remaining 96 frames of subcodes. However, among one byte subcodes (each bit is represented by P through W), data for searching a track has been already allocated for data in P and Q channel. Then, graphic data may be allocated with 6 bits in the remaining R channel through W channel. That is, a substantial range in which the graphic data can be allocated is 6×96 bits.
Because one block data is transmitted with a frequency of 75 Hz, an amount of one frame of data transferred is 75×98 Hz. Accordingly, the bit rate for transmitting the subcodes is 7.35 kbyte/s.
FIG. 23
shows a transmission format of such graphic data. As shown in the figure, a packet is composed of 96 symbols of data, with one symbol being 6 bit data from R channel through W channel, and each packet is composed of four packs. Each pack is composed of 24 symbols from symbol
0
to symbol
23
. Mode information is allocated to three bits of R, S and T in the symbol
0
and item information is allocated to three bits of U, V and W, respectively. The following modes are defined by combining such modes and items:
MODE
ITEM
000
000 Zero Mode
001
000 Graphic Mode
001
001 TV-graphic Mode
111
000 User Mode
Then, an instruction is allocated to the symbol
1
and the mode and parity bits for the item and instruction are allocated to the symbols
2
and
3
, so that a substantial range to which graphic data can be allocated is 12 symbols, for example, as shown in
FIG. 23
among the symbols from symbol
4
through symbol
19
. Parity bits for 20 symbols from the symbol
0
through symbol
19
are allocated to four symbols from symbol
20
through symbol
23
.
Graphic data can be thus allocated as binary data in the range of 6×12 pixels of each pack in the CD-G. Because the rate of the pack is 75×4=300 packs/s, 300 characters may be transmitted per one second if one character is allocated in this range of 6×12 pixels.
Further, because one screen defined in the CD-G is 288 horizontal pixels×192 lines, it takes 2.56 seconds to transmit this one screen of characters as shown in the following expression:
(288/6)×(192/12)/300=2.56
Still more, because different patterns have to be transmitted four times per one character pattern if a hexadecimal representation is made in each pixel, it takes 10.24 seconds which is four times of the above time.
By the way, among such conventional methods, there has been a disadvantage that an user cannot turn on or off a displayed subtitle arbitrary in the method by which the subtitle superimposed on a video image is transmitted, like the video disk and normal TV broadcasting. Further, there has been another disadvantage in them that they do not allow to prepare subtitles in a plurality of languages and to let the user select certain one.
Contrary to that, although the method in the CAPTAIN system and CD-G allows to arbitrary turn on off the display of the subtitle, it has a disadvantage that its resolution is not good enough.
That is, whereas a displayable area of one screen is 248 horizontal pixels×192 lines in the CAPTAIN system, component digital TV signal has a resolution of 720 horizontal pixels×480 lines, and it can be seen that the resolution of the former is not as good as compared to the resolution of the latter.
Furthermore, because only one bit data can be accommodated per one pixel in the CD-G, data is represented by binarizing it. Accordingly, there has been a disadvantage that such phenomena as an aliasing phenomenon by which slanted portions of a character appears in zig-zag and a flicker phenomenon by which characters flicker become significant, giving an unpleasant feeling to the user.
Although it is conceivable to convert the binary information to multi-valued information by means of a filter for example, it requires a high precision filter and hence increases the cost. The use of such filter may also degrade the background image.
If one pixel is represented in hexadecimal in the CD-G, it takes about four times the amount of time when it is displayed in binary and it becomes difficult to switch the display of subtitles quickly. Further, because the data rate is low in the method in the CAPTAIN system and CD-G, it has been difficult to display subtitles which dynamically change timewise.
Accordingly, it is an object of the present invention to solve the aforementioned problems by providing means which allows to display a high quality subtitle in accordance to a preference of an user, to switch the display of the subtitle quickly without degrading the background video image and to display the subtitle which dynamically changes timewise with less data amount.
SUMMARY OF THE INVENTION
The subtitle data encoding unit of the present invention for encoding a subtitle to be superimposed on a video image and to be displayed comprises a color lookup table (CLUT)
71
as memory means for storing color data and a color quantization circuit
70
as detecting means for detecting an address in the CLUT
71
for storing color data which corresponds to a color of the subtitle, and is characterized in that the address detected by the color quantization circuit
70
is transmitted as color information concerning on the color of the subtitle.
The subtitle data encoding unit is characterized in that it transmits, in addition to the color information, pattern information concerning on a pattern of the subtitle and a repeat time which is a number of vertical synchronous signals in the video image on which the subtitle is continuously superimposed.
The subtitle data encoding unit for encoding a subtitle to be superimposed on a video image and to be displayed comprises range specifying means (e.g., Step S
53
in a program in
FIG. 16
) for specifying a range in which the subtitle is to be displayed, bit number determining means (e.g., Step S
55
in the program in
FIG. 16
) for determining a bit number per one pixel in quantizing the subtitle, encoding means (e.g., Step S
58
in the program in
FIG. 16
) for encoding in correspondence with values determined by the range specifying means and bit number determining means, and correcting means (e.g., Step S
60
in the program in
FIG. 16
) for correcting the values determined by the range specifying means and bit number determining means in correspondence with an amount of codes encoded by the encoding means.
This subtitle data encoding unit may be further provided with adjusting means (e.g., Step S
54
in the program in
FIG. 16
) for adjusting a horizontal resolution of the subtitle.
The recording medium according
Lee Michael
Limbach & Limbach L.L.P.
Oh Seong Kun
Sony Corporation
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