 |
Claims  |
|
|
I claim:
1. Apparatus comprising:
a source of digital packets representing analog video signals in compressed
form;
a decoder for producing a sequence of digital words representing respective
components of a video image corresponding to said analog video signal and
organized in repetitive video image groups in response to said digital
packets; each of said video image groups corresponding to two picture
elements and including a first luminance component corresponding to a
first picture element of said two picture elements, a second luminance
component corresponding to a second picture element of said two picture
elements, and two color difference components corresponding to each of
said two picture elements;
a memory for storing a sequence of digital words representing respective
components of a graphics image and organized in repetitive graphics image
groups; each of said graphics image groups corresponding to one picture
element and including a luminance component and two color difference
components corresponding to said picture element;
a converter coupled to said memory for converting respective pairs of
sequential graphics image groups stored in said memory to new graphic
image groups; each of said new graphics image groups corresponding to two
picture elements and including a first luminance component corresponding
to a first picture element of said two picture elements, a second
luminance component corresponding to a second picture element of said two
picture elements, and two color difference components corresponding to
each of said picture elements; and
a multiplexer responsive to said video image groups and to said new
graphics image groups for selecting either said video image groups or said
graphics image groups to produce a sequence of resultant image groups;
each of said resultant image groups corresponding to two picture elements
and including a first luminance component corresponding to a first picture
element of said two picture elements, a second luminance component
corresponding to a second picture element of said two picture elements,
and two color difference components corresponding to each of said two
picture elements.
2. The apparatus recited in claim 1, further including:
a second converter responsive to said sequence of resultant image groups
for producing a sequence of output image groups in which respective ones
of said resultant image groups have been converted to respective pairs
output image groups; each of said pairs of output image groups
corresponding to one picture element; a first one of said output image
groups including said first luminance component and said two color
difference components of a respective one of said resultant image groups;
a second one of said output image groups including said second luminance
component and said two color difference components of said respective one
of said resultant image groups.
3. The apparatus recited in claim 2, further including:
a digital to analog converter for converting said sequence of output signal
groups to respective analog video signal components.
4. The apparatus recited in claim 1, wherein:
a first of said two color difference components represents the difference
between the respective luminance component and first primary color; and a
second of said two color difference components represents the difference
between the respective luminance component and second primary color.
5. The apparatus recited in claim 1, wherein:
said memory includes a section operatively coupled with said decoder.
6. Apparatus comprising:
a source of a sequence of digital words representing respective components
of a video image and organized in repetitive video image groups; each of
said video image groups corresponding to two picture elements and
including a first luminance component corresponding to a first picture
element of said two picture elements, a second luminance component
corresponding to a second picture element of said two picture elements,
and two color difference components corresponding to each of said two
picture elements;
a memory for storing a sequence of digital words representing respective
components of a graphics image and organized in repetitive graphics image
groups; each of said graphics image groups corresponding to one picture
element and including a luminance component and two color difference
components corresponding to said picture element;
a converter coupled to said memory for converting respective pairs of
sequential graphics image groups stored in said memory to new graphic
image groups; each of said new graphics image groups corresponding to two
picture elements and including a first luminance component corresponding
to a first picture element of said two picture elements, a second
luminance component corresponding to a second picture element of said two
picture elements, and two color difference components corresponding to
each of said two picture elements; and
a multiplexer responsive to said video image groups and to said new
graphics image groups for selecting either said video image groups or said
graphics image groups to produce a sequence of resultant image groups;
each of said resultant image groups corresponding to two picture elements
and including a first luminance component corresponding to a first picture
element of said two picture elements, a second luminance component
corresponding to a second picture element of said two picture elements,
and two color difference components corresponding to each of said two
picture elements.
7. The apparatus recited in claim 6, further including:
a second converter responsive to said sequence of resultant image groups
for producing a sequence of output image groups in which respective ones
of said resultant image groups have been converted to respective pairs
output image groups; each of said pairs of output image groups
corresponding to one picture element; a first one of said output image
groups including said first luminance component and said two color
difference components of a respective one of said resultant image groups;
a second one of said output image groups including said second luminance
component and said two color difference components of said respective one
of said resultant image groups.
8. The apparatus recited in claim 7, further including:
a digital to analog converter for converting said sequence of output signal
groups to respective analog video signal components.
9. The apparatus recited in claim 6, wherein:
a first of said two color difference components represents the difference
between the respective luminance component and first primary color; and a
second of said two color difference components represents the difference
between the respective luminance component and second primary color.
10. Apparatus comprising:
a source of a sequence of digital words representing respective components
of a video image and organized in repetitive video image groups; each of
said video image groups corresponding to a number N, more than one, of
picture elements and including a number N of luminance components
corresponding to respective ones of said N picture elements and two color
difference components corresponding to each of said N picture elements;
a memory for storing a sequence of digital words representing respective
components of a graphics image and organized in repetitive graphics image
groups; each of said graphics image groups corresponding to one picture
element and including a luminance component and two color difference
components corresponding to said picture element;
a converter coupled to said memory for converting respective ones of said
graphics image groups stored in said memory to new graphic image groups;
each of said new graphics image groups corresponding to N picture elements
and including N luminance components corresponding to respective ones of
said N picture elements and two color difference components corresponding
to each of said N picture elements; and
a multiplexer responsive to said video image groups and to said new
graphics image groups for selecting either said video image groups or said
graphics image groups to produce a sequence of resultant image groups;
each of said resultant image groups corresponding to N picture elements
and including N luminance components corresponding to respective ones of
said N picture elements and two color difference components corresponding
to each of said N picture elements. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
CROSS REFERENCE TO RELATED APPLICATION
This application is related to U.S. patent application Ser. No. 08/261,623
entitled "On Screen Display Arrangement for a Digital Video Signal
Processing System" filed in the name of B. W. Beyers, Jr. on the same day
as this application and assiged to the same assignee.
1. Field of the Invention
The invention concerns an "on screen display" (OSD) arrangement for a
digital video signal processing system.
2. Background of the Invention
On screen display (OSD) arrangements employed in video processing systems
include a switching (or "multiplexing") network for switching between
graphic image representative signals and normal video signals so that a
graphic image can be displayed on the screen of a picture reproduction
device either in place of the image represented by the video signals or
together with (inserted in) the image. The graphic image can take the form
of alphanumeric symbols or pictorial graphics, and can be used to indicate
status information, such as channel numbers or time, or operating
instructions.
In an OSD arrangement for use in an analog video signal processing system,
the multiplexing network typically operates to switch in levels
corresponding to the desired intensity of respective portions of the
graphic image at the time the graphic image portions are to be displayed.
In such an arrangement the graphic image representative signals take the
form of timing pulses which occur when the graphic image portions are to
be displayed and are used to control the multiplexing network. Such an
analog OSD arrangement can also be used in a digital video processing
system, but requires that the video signals be first converted to analog
form. While digital video signal processing systems typically include a
digital-to-analog converter section in which the digital video signals are
converted to analog form, it may be more cost effective for the OSD
arrangement to be incorporated as an integral part of the digital video
processing section.
SUMMARY OF THE INVENTION
The invention concerns a digital OSD arrangement for a digital video signal
processing system, and especially one for a digital video processing
system in which the digital video signals represent image information in
compressed form.
More specifically the invention concerns an OSD arrangement for a digital
video processing system which includes a source of a sequence of digital
words representing respective components of a video image. The video image
component representative digital words are organized in groups
corresponding in a compressed form to more than one picture element. For
example, the groups may correspond to two picture elements and may include
first and second luminance components corresponding to respective ones of
the two picture elements, and two color difference signals corresponding
to each of the two picture elements. A memory stores digital words
representing respective components of a graphics image. The graphic image
component representative digital words are organized in groups
corresponding in uncompressed form to respective picture elements. For
example, the groups may include the luminance and a pair of color
difference components corresponding to respective picture elements. A
converter converts the graphic representative image groups stored in the
memory to new groups of graphic image representative groups which are of
the same form as the video image representative groups to make it possible
to multiplex the video image representative groups and the graphics image
representative groups. For example, the converter produces new graphic
representative groups which include first and second luminance components
corresponding to respective ones of the two picture elements, and a pair
of color difference signals corresponding to each of the two picture
elements. A multiplexer selects either ones of the video image
representative groups or ones of the graphics image representative groups
to produce a sequence resultant image representative groups.
These and other aspects of the invention will be described with respect to
the accompanying Drawing.
BRIEF DESCRIPTION OF THE DRAWING
In the Drawing:
FIG. 1 is a block diagram of a digital satellite television system
including a digital signal processing section including a digital OSD
arrangement as an integral part in accordance with an aspect of the
invention;
FIG. 2 is a block diagram which disclosed details of the digital video
signal processing section of the digital satellite television system shown
in FIG. 1 the digital OSD arrangement; and
FIG. 3 is a block diagram of a converter used in the OSD arrangement shown
in FIG. 2.
DETAILED DESCRIPTION OF THE DRAWING
In the satellite television system shown in FIG. 1, a transmitter 1, with
an associated transmitting antenna 3, transmits television signals
including video and audio components to a satellite 5 in geosynchronous
earth orbit. Satellite 5 receives the television signals transmitted by
transmitter 1 and retransmits them toward the earth. The television
signals transmitted by satellite 5 are received by an antenna assembly or
"outdoor unit" 7. Antenna assembly 7 includes a dish-like antenna 9 and a
frequency converter 11. Antenna 9 directs the television signals
transmitted from satellite 5 to frequency converter 11 which converts the
frequencies of all the received television signals to respective lower
frequencies. Frequency converter 11 is often called a "block converter"
since it converts the frequency band of all of the received television
signals as a block.
The television signals produced by block converter 11 are coupled via a
coaxial cable 13 to a satellite receiver 15. Satellite receiver 15 is
sometimes referred to as an "indoor unit" because it is located indoors.
Satellite receiver 15 tunes, demodulates and otherwise processes the
received television signal as will be described in detail below to produce
video and audio signals with a format (NTSC, PAL or SECAM) suitable for
processing by a conventional television receiver 17 to which they are
coupled. Television receiver 17 produces an image on a display screen 19
in response to the video signals and an audible response by means of
speakers 21a and 21b in response to the audio signals.
The satellite television system shown in FIG. 1 is a digital television
satellite system in which television information is transmitted in
compressed form in accordance with a predetermined digital compression
standard such as MPEG. MPEG is an international standard for the coded
representation of moving pictures and associated audio information
developed by the Motion Pictures Expert Group.
More specifically, within transmitter 1, analog video signals and analog
audio signals are converted to respective digital signals. The digital
video and audio signals are compressed and encoded according to the MPEG
compression and encoding standard. The resultant encoded digital signal
has the form of a series or stream of packets corresponding to respective
video and audio components. The type of packet is identified by a header
code. Packets corresponding to control and other data may also be added
the data stream.
In the MPEG standard, the video information is transmitted in the form of a
luminance (Y) component and two color difference (U and V) components. For
example, the first color difference component may represent the difference
between the red image information and the luminance image information
(R-Y) and the second color difference component may represent the
difference between the blue image information and the luminance image
information (B-Y). In addition, the color information is compressed
because the two color difference components correspond to more than one
picture element. The use of color difference components and the sharing of
the color difference components between picture elements reduces the
transmission bandwidth.
Forward error correction (FEC) data is added to the packets in order make
the correction of errors due to noise within the transmission path
possible. The well known Viterbi and Reed-Solomon types of forward error
correction coding may both be advantageously employed. The digital
information resulting from the compression, encoding and error correction
operations is modulated on a carrier in what is known in the digital
transmission field as QPSK (Quaternary Phase Shift Keying) modulation.
Satellite receiver 15 includes a tuner 1501 with a local oscillator and
mixer (not shown) for selecting the appropriate carrier signal form the
plurality of signals received from antenna assembly 7 and for converting
the frequency of the selected carrier to a lower frequency to produce an
intermediate frequency (IF) signal. The IF signal is demodulated by a QPSK
demodulator 1503 to produce a demodulated digital signal. A FEC decoder
1505 decodes the error correction data contained in the demodulated
digital signal, and based on the error correction data corrects the
demodulated packets representing video, audio and other information. For
example, FEC decoder 1505 may operate according to Viterbi and
Reed-Solomon error correction algorithms when Viterbi and Reed-Solomon
error correction encoding is employed in transmitter 1. Tuner 1501, QPSK
demodulator 1503 and FEC decoder 1505 may be included in a unit available
from Hughes Network Systems of Germantown, Md. or from Comstream Corp.,
San Diego, Calif.
A transport unit 1507 is a demultiplexer which routes the video packets of
the error corrected signal to a video decoder 1509 and the audio packets
to an audio decoder 1511 via a data bus according to the header
information contained in the packets.
Video decoder 1509 cooperates with a random access memory (RAM) 1513 for
example, in the form of a dynamic RAM (DRAM), to decode and decompress the
video packets to form a stream or sequence of digital words representing
respective luminance (Y) and color difference (U and V) components. The
sequence of video component representative digital words is coupled to a
television encoder 1515 which converts the component representative
digital words to a sequence of digital words representing luminance (Y)
information and a sequence of digital words representing chrominance (C)
information in accordance with the line and field raster scanning format
of a conventional television standard such a NTSC, PAL or SECAM.
Television signal encoder 1515 generates line (H) and field (V) rate
signals and a picture element (pixel) clock signal (P) which are coupled
to video decoder 1509 to synchronize the component representative sequence
of digital words. The luminance and chrominance representative digital
words are converted to analog luminance and chrominance signals by
respective sections of a digital-to-analog converter (DAC) 1517.
Audio decoder 1511 decodes and decompresses the audio packets and the
resultant digital audio signal is converted to a baseband analog audio
signal by a DAC 1519. Although only a single audio channel is indicated in
FIG. 1, it will be appreciated that in practice one or more additional
audio channels, for example, for stereophonic reproduction, may be
provided as is indicated by speakers 21a and 21b.
The baseband analog video and audio signals are coupled to television
receiver 17 via respective baseband connections. The baseband analog video
and audio signals are also coupled to a modulator 1521 which modulates the
analog signals on to a radio frequency (RF) carrier in accordance with a
conventional television standard such as NTSC, PAL or SECAM for coupling
to the antenna input of a television receiver without baseband inputs.
A microprocessor 1523 provides frequency selection control data to tuner
1501 for controlling the operation of tuner 1501 to tune channels selected
by the user. Microprocessor 1523 also operates interactively with
transport 1507 to affect the routing of data packets. Microprocessor 1523
additionally provides control data to video decoder 1509 and audio decoder
1511 via a control bus.
Still further, microprocessor 1523 generates control data for causing
graphics images, such as alphanumeric characters and/or pictorial
graphics, for example, representing status information and operating
instructions, to be displayed on screen 19 of television receiver 17. The
graphics data specifies the color and position of each picture element
(pixel) of the graphics which are to be displayed. The graphics data
represents a pixel by pixel map or "bit map" of the graphic image.
Advantageously, the remaining portion of the on screen display (OSD)
arrangement is integrally incorporated in video decoder 1509 and
associated video RAM 1513, which are primarily used for the decoding and
decompression of the video data packets. The graphics data is coupled to
video decoder 1509 via the control bus. As a result of the shared use of
video decoder 1509 and associated video RAM 1513, a separate OSD
arrangement is not needed. Details of the OSD arrangement will be
described with respect to FIG. 2.
Video decoder 1509 is incorporated in a single integrated circuit (IC).
Similar video decoding and decompression ICs, with the exception of the
OSD provisions to be described below, are commercially available. For
example, a MPEG decoding and decompression IC, identified by part number
ST3240, is available from SGS Thomson, of France. While the details of the
portions of video decoder 1509 concerned with the decoding and
decompression of the video data packets is not necessary to understanding
the OSD provisions, the following brief description of those portions is
helpful.
Video decoder 1509 includes a FIFO (first in, first out) buffer memory
1509-1 which receives video data packets on demand in relatively small
segments from transport 1507 and which couples them in relatively larger
segments via a memory controller 1509-3 to a section 1513-1 of RAM 1513
reserved for decoding and decompression. Video RAM 1513 is addressed under
the control of memory controller 1509-3. Decoding and decompression
section 1513-1 of RAM 1513 includes a rate buffer section 1513-1-3 for
storing the received video data packets and a frame store section 1513-1-5
for storing frames of video information during the decoding and
decompression operation. A video image display unit 1509-5 decodes and
decompresses the stored video data packets to form the sequence of video
image component representative digital words (Y, U, V). For this purpose,
video display unit 1509-5 requests data from decoding and decompression
section 1513-1 of video RAM 1513 via memory controller 1509-3 as required.
The generation of the component representative digital words is
synchronized with the field (V), line (H) and pixel (PC) rate signals
generated by television signal encoder 1515. Control data generated by
microprocessor 1523 is received by a microprocessor interface unit 1509-7
and coupled to various portions of video decoder 1509 via an internal
control bus.
The number of bits contained in the video image component representative
digital words determine the number of possible levels and thereby the
resolution of the respective components. For n-bit words there are 2.sup.n
possible levels corresponding to the 2.sup.n possible binary states. By
way of example, in the present embodiment, the video image component
representative word contain eight bits and therefore each component can
have 2.sup.8 or 256 possible levels. The sequence of video image component
representative digital words is organized in groups of components in which
each group corresponds to plurality of pixels in subsampled or compressed
form. More specifically, in the present embodiment, the video image
representative groups correspond to two pixels, each of which includes a
first luminance representative digital word (Y.sub.1) corresponding to a
first pixel, a second luminance representative digital word (Y.sub.2)
corresponding to a second pixel, and a single pair of color difference
representative digital words (U.sub.1,2 and V.sub.1,2) corresponding to
each of the first and second pixels. This has been referred to as a
"4:2:2" format in the digital video signal processing field. The
subsampling or compression of the color difference signals relates to the
image data compression which occurs in the transmitter 1 for the purpose
of reducing the transmission bandwidth. More specifically, the transmitted
image data is organized in what is known as 4:2:0 format in which the
image representative words correspond to four pixels in which there are
four luminance representative words corresponding to respective ones of
four pixels and a single pair of color difference representative words
corresponding to each of the four pixels. The 4:2:0 image representative
groups are converted to 4:2:2 image representative groups by interpolation
within video display unit 1509-5. A complete set (4:4:4) of components for
each pixel is produced by interpolation within television signal encoder
1515.
The OSD portion of video decoder 1509 includes an OSD controller 1509-9
which cooperates with an OSD section 1513-3 of video RAM 1513. The
graphics representative bit map generated by microprocessor 1523 is
coupled via microprocessor interface unit 1509-7 and memory controller
1509-3 to OSD section 1513-3 of RAM 1513 for storage. For each pixel of
the graphic image there is a digital word representing a color for that
pixel. The number of bits contained in the color representative digital
words determines how many different colors each pixel can have. If the
color representative words contain n bits, then each pixel can have any
one of 2.sup.n colors corresponding to the 2.sup.n possible binary states
of the n-bit color word. By way of example, in the present embodiment, the
color representative words contain two bits. Accordingly, each graphics
pixel can have any one of four colors corresponding to the four possible
binary states (00, 01, 10, and 11) of the two-bit color word. The pixel
color information is organized in a component form in which for each color
word there is a unique group of component representative digital words.
The components are selected to be the same as the components used for the
transmission of video image information: namely, luminance (Y) and a pair
of color differences signal (U and V). The selection of the same
components for video images and graphics images simplifies the OSD
arrangement because it avoids the need for conversion from one set of
components to another. For example, in the present embodiment which
utilizes two-bit color words, the following relationship between the color
representative digital words and the groups of component representative
digital words exits:
______________________________________
color group of components
______________________________________
00 Y.sub.A, U.sub.A, V.sub.A
01 Y.sub.B, U.sub.B, V.sub.B
10 Y.sub.C, U.sub.C, V.sub.C
11 Y.sub.D, U.sub.D, V.sub.D
______________________________________
The actual color (represented by the subscripts A, B, C or D in the table)
of a graphics pixel depends on the value represented by component
representative digital words of the respective group. By way of example,
in the present embodiment, the graphic image component representative
words each contain four bits. Four-bit component representative words
provide 16 possible levels for each component. The four bits represent the
most significant bits of an eight-bit word which is eventually formed by
OSD display unit 1509-9, as will be described below.
The graphic image component representative words are transmitted to and
stored in OSD section 1513-3 of RAM 1513 from microprocessor 1523 in
component groups as is indicated in the table in the form of a header for
the bit map. In the present embodiment, in which each graphic image
component representative digital word contains four bits, each group
includes 12 bits. The colors of a graphics image may be changed by
changing the four bits of one of more component representing words of the
header, depending on the nature of the graphics image to be displayed.
OSD display unit 1509-9 causes the bit map to be read out from OSD section
1513-3 of RAM 1513, and converts the color representative word for each
pixel to the corresponding component representative group from the header.
For this purpose, OSD display unit 1509-9 requests data from OSD section
1513-3 via memory controller 1509-3 as required. Since, in the present
embodiment the graphic image component representative words contain only
four bits while the video image representative words contain eight bits,
OSD display unit 1509-9 converts the four-bit graphic image component
representative words to eight-bit words by simply adding four binary "0s"
as the least four significant bits to the four-bit words. The generation
of the graphic image component representative digital words by OSD display
unit 1509-9 is also synchronized with the field (V), line (H) and pixel
(PC) rate signals generated by television signal encoder 1515.
As earlier noted, the video image component representative groups generated
by video image display unit 1509-5 represent video image information in a
compressed form in which for every two pixels there are two respective
luminance representative words and one pair of color difference
representative words in a so-called 4:2:2 format. On the other hand, the
graphic image component representative groups stored in OSD section 1513-3
of RAM 1513 and generated by OSD display unit 1509-9 represent graphics
image information in an uncompressed form in which for every one pixel
there is one luminance representative word and one pair of color
difference representative words (or for every two pixels there are two
respective luminance representative words and two respective pairs of
color difference representative words). The latter uncompressed format has
become known as the "4:4:4" format in the digital video signal processing
field. The 4:4:4 graphics image sequence is desirable since it allows as
many colors as possible to be defined with a given number of bits because
it provides for a unique luminance component and two unique color
difference components for each pixel of graphics. However, the 4:4:4
graphic image sequence is not compatible with the 4:2:2 video image
sequence and cannot be readily multiplexed with it to so as to insert a
graphic image into a video image.
To solve this problem, video decoder 1509 includes an OSD converter 1509-11
for converting the 4:4:4 sequence used for the graphic image components to
the 4:2:2 sequence used for the video image components. As is pictorially
indicated in FIG. 2, for every two graphics pixels, converter 1509-11
selects the pair of color difference components for the first pixel and
deletes the pair for the second pixel. As shown in as shown in FIG. 3, OSD
converter 1509-11 may comprise a latch 1509-11-1 for storing two groups of
graphic image component representative words, and a multiplexer 1509-11-3
which selects the appropriate component representative words in sequence
from those stored in latch 1509-11-1 at the output rate. It is desirable
that the number of 4:4:4 groups of graphic image representative components
per line be an even number because two of the original 4:4:4 graphic image
groups are used to produce each new one of the 4:2:2 graphic image groups.
While the output sequence is shown as being, in the order named, a first
luminance (Y) component for a first pixel of two pixels, a first color
difference component (U) for each of the two pixels and a second color
difference component (V) for each of the two pixels, and a second
luminance component for the second of the two pixels, other output
sequences may be used. For example, the output sequence may be, in the
order named, a first color difference component (U) for each of the two
pixels, a first luminance (Y) component for a first pixel of two pixels, a
second color difference component (V) for each of the two pixels, and a
second luminance component for the second of the two pixels.
An output multiplexer 1509-13 selects either groups of video image
component representative words provided by video display unit 1509-5 or
groups of graphic image component representative words provided by OSD
converter 1509-11 under the control of OSD display unit 1509-9. In a video
image only mode of operation, output multiplexer 1509-13 selects only the
video image groups. In a graphic image only mode of operation, output
multiplexer 1509-13 selects only the graphic image groups. In a
"superimpose" mode of operation, in which the graphic image is inserted
within a video image, output multiplexer 1509-13 selects either the video
image groups or the graphic image groups on a pixel by pixel basis. The
4:2:2 output sequence of component representative words produced by output
multiplexer 1509-13 is coupled to television signal encoder 1515.
* * * * *
|
|
|
|
|
|
|
Description |
|
