JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
ELECTRONICS AND COMMUNICATION ENGINEERING
DIGITAL REVOLUSION -MOTION PICTURE
COMPRESSION TECHNIQUES
1Charmy
Patel, 2Dr.G.R.Kulkarni
1Research
scholar Department of Electronics & Communication Engineering, Singhania
university,junjuhnu,jaipur-Rajsthan,India
Gujarat, India
2Principal of Shri C.U.Shah College of engineering and Technology Vadhvan city Gujarat, India
charmychangela@gmail.com
ABSTRACT: Digital television broadcasting is present and future of television. With the advent of digital
technology, digital audio and video compression and other advanced signal processing, it is possible to
transmit and receive broadband data over co-axial cable and through satellite and terrestrial. Digital television
is a telecommunication system for broadcasting and receiving moving picture and sound by means of digital
signals, in contrast to analogue signals in analogue (traditional) Television. It uses digital modulation data,
which is digitally compressed and requires decoding by a specially designed television set or a standard
receiver with a set-top box. For all delivery mechanism a digital set-top box is needed at the customer’s
premises. It receives the digital transmission and decodes video, audio programs to display on normal
Television Receiver. Digital television is practically and economically not feasible without motion picture
compression technique. The main goal of any conditional access system is to control viewer’s access to digital
television pay services and secure the service providers revenue streams.
Keywords – digital video, spectral coding, spatial coding, MPEG, predictive picture
I INTRODUCTION TO DIGITAL TELEVISION
Digital Television is completely new way of
broadcasting and is the future of television. It is a
medium that requires new thinking and new revenuegenerating business models. Digital Television is the
successor to analog Television and eventually all
broadcasting will be done in digital format. Around
the globe, Satellite, Cable and Terrestrial operators
are moving to a digital environment. The digital age
will improve the consumer viewing experience
through cinema-quality pictures, CD –quality sound,
hundreds of new channels. Digital television also
opens up a new world of opportunities for companies
who want to develop content and applications for the
new paradigm. This includes the creative
communities within the Television and film industry,
internet content providers and software development
houses. Finally, the new medium will allow viewers
from the comfort of their homes to use a simple
remote control to electronically purchase goods and
service offered by various content providers. In
existing Television system the input signal at the
camera and the output to the picture tube are analog.
If digital technique is to be used for Television
system the composite video signal must be digitized
i.e. a binary sequence of 0’s and 1’s must be used.
Digital television uses the same language as
computers- a long stream of binary digits, each of
which is either 0 or 1. With digital television the
signal is compressed and only the updated data
transmitted. As a result, it is possible to squeeze 6 or
8 channels into frequency range that was previously
occupied by only one analog Television channel.
Digitization of the composite video signal involves
high speed analog to digital converters and very high
bit rates for transmission. The problem of high speed
conversion and high bit rate for transmission has been
solved with the emergence of Broadband- Integrated
Services Digital Network (B-ISDN). In 1982 CCIR
has unanimously adopted the ‘Recommendation 601’
for encoding parameter of digital Television for
Studios. An arrangement has been made on a digital
code compatible with both 525/60 and 625/50
standards.
II TECHNICAL BACKGROUND OF
TELEVISION
The analog video format is based on the PAL/NTSC
composite video signals, the standards used in Europe
and the USA respectively. Black and white video
consisted of a single luminance Y signal, which
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indicated the brightness of pixels on the screen. This
signal had a bandwidth of about MHz.
When colour television was introduced, the video
developers needed to maintain backwards
compatibility, with the Black and White system. For
this reason, the Y signal was maintained and the
colour information was added in via the
chrominance (C) signal. The C signal was positioned
within the same spectrum as the Y signal at about
4.3MHz (PAL). The C signal is further composed of
two colour difference signals, U and V, which are
Quadrature Amplitude Modulated to form the C
signal. This gives the U V Y format for the colour
composite video signal.
At the television receiver the U V Y format is
converted in to RGB format, which informs the CRT
what proportion of Red, Green and Blue light to shine
on each pixel on the screen. The U V Y format is
therefore a compressed way of transmitting the
sequence of RGB frames, which make up the video
signal.
For digital transmission, the video must be digitized
first using and A/D converter. The video is
converted in to samples with, for example, 8bits per
sample. The data is now simply a bit stream, which
can be manipulated by computer.
II.1 video signal after digitization
Chrominance (Y): 13.5MHz
Chrominance (Cr): 6.75MHz
Chrominance (Cr): 6.75MHz
Quantization : 8bit/sample
Total bits per second:
(13.5 + 6.75 +6.75)*8= 216M bits
Total BW required : 108 MHz
II.2 Digital Television with compression
MPEG (Moving Picture Expert Group)
The acronym MPEG stands for moving picture expert
group, which workd to generate the spccifications
under ISO, the International Organization for
Standardization and IEC, the International
Electrotechnical Commission.
What is commonly referred to as ‘MPEG Video”
actually consists at the present time of two finalized
standards, MPEg-1 and MPEG-2 with a third
standard, MPEG-4, was finalized in 1998 for very
low bit rate audio-visual coding. The MPEG-1 and
MPEG-2 standards are similar in basic concepts.
They both are based on motion compensated block
based transform coding techniques, while MPEG-4
deviates from these more traditional approaches in its
usage of software image construct descriptors, for
target bit-rate in the very low range.
Because MEPG-1 and MPEG-2 are finalized
standards and are both presently being utilized in a
large number of applications this report concentrates
on compression techniques relating only to these two
standards.
Note that there is now reference to MPEG-3.This is
so because it was originally anticipated that this
standard would refer to HDTV application, but it was
found that minor extensions to MPEG-2 standard
would suffice for this higher bit-rate, higher
resolution application, so work on a separate MPEG3 standard was abandoned.
To understand the concept of motion picture
compression technique we can compare it with
orange juice analogy as shown in fig. 1
Fig:1 comparision of compresion with orange juice
analogy
 Filtering the video signal to remove the noice
etc. otherwise it may corrupt the video
signals.like washing of oranges.
 Removing unwanted information from the
video signals like removing peel, seed, skin
from oranges.
 By digitization process converting analog
video into digital video like crusing process
converting orange from orange juice.
 Asignificant amount of informationcontent in
the video signal is redundant. An expensive
encoder is used to remove the information
from digirized video signal without
destroying its quality like water content in
orange juice is redundant. An expensive
plant is used to remove the redundant water
content from the orange juice without
destroying its quality.
 Output of the encoder is digital video whose
no of bits are much less than the bits of the
digitize video fed to the encoder like the
output of the plant is pulp whose physical
quantity is less than the orange juice quantity
fed to the plant.
 The bits of compressed digital video are
convered into small packets. Hearder of each
packet contains necessary information such
as name, number of bits, and direction for
decoding to convert it into almost like
original video signal like the orange pulp is
packed in small tins. Necessary information
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



such as name of company, details of
ingredients, weight, directions for handling
and converting pulp into almost like fresh
orange juice.
Packets of bits are multiplexed to form group
of pictures. These are now ready for storage
in hard disc or transmission by modulating
on carrier, like small sealed orange tins are
packed
into
big
cartons
for
storage/transportation. These tins in the
carton are transported by some carriers.
The decoder on receiving the packets converts
the compressed bits into almost like original
video signal as per the information given in
the header, like consumer followes the
instructions written on each tin to prepare
almost like fresh orange juice from the pulp.
For this he is required to add correct
quantity of water and ice etc.
The decoding process of converting
compressed bits in to video signal is much
simpler than encoding process. Therefore
decoders are cheaper and less complicated
than encoder, like the process of making
orange juice from the pulp is very simple as
compared to the process of converting
orange juice into pulp.
Encoder is like a black box. The
manufacturer does not specify, How coding
is done. It is their trade secret .only bit
stream and decoding format is described,
like manufacturer does not specify how
exactly pulp is prepared. It is trade secret.
They only specify its ingredients and
instruction about how to prepare orange
juice from the pulp.
II.3 types of redundancy in video signal
 Spectrum redundancy
 Spatial redundancy
 Temporal redundancy
 Entropy redundancy
 Psycho-visual redundancy
II.4 coding techniques for compression
Spectral coding
Spatial coding
Temporal coding
II.4.1 Spectral coding
The RGB signals form video cameras are highly
correlated and take on large bandwidth
To decrease the amount of video sample data based
on human perception, the RGB color space is
converted to Y Cr Cb color space.
The y has the full bandwidth as it is very sensitive to
human perception. The Cr and Cb components have
a narrower bandwidth because these are less
discernible by human eye. The chrominance
components are usually decimated by two, both
horizontally and vertically resulting in a reduced
number of samples.
II.4.2 Spatial coding
Video signal exists in four dimensions
i. The magnitude of the sample
ii. The horizontal spatial axis
iii. The vertical spatial axis
iv. The time axis
Since spatial coding is confined only to individual
frame therefore it works in three dimensions only is
on the horizontal and vertical spatial axis and on the
sample values.
In a picture, where there is a high spatial frequency
content due to detailed areas of the picture, there is a
relative small amount of energy at such frequency.
Also picture may contain sizeable areas in which the
same or similar picture values exist. This give rise to
low spatial frequency contents e.g. areas of sky or
grassland. The average brightness of the picture
results in a substantial zero frequency (DC)
components.
Simply omitting the high frequency components is
unacceptable as this causes an obvious softening of
the picture. Human eye’s sensitivity to noise in high
spatial frequencies is less. This is used for the coding
gain. Coding gain is obtained b taking advantage of
the fact that the amplitude of the spatial components
falls with frequency. if the spatial spectrum is divided
into frequency bands the high frequency bands can be
described by fewer bits not only because their
amplitudes are smaller but also because more noise
can be tolerated.
Fig: 2 block diagram of spatial coding process
II.4.3Temporal coding
Temporal coding or inter coding takes advantage of
the similarities between successive pictures in real
material. Instead of sending information for each
picture separately, inter coders will send the
difference between the previous picture and the
current picture in a form of differential coding. A
picture store is required at the coder to allow
comparison to be made between successive pictures
and a similar store is required at the decoder to make
the previous picture available.
The difference data may be treated as a picture it self
and subjected to some form of transform based
compression.
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Motion compensation is a process which effectively
measures motion of objects from one picture to the
next so that it can allow for that motion when looking
for redundancy between pictures.
correction. A coding error in this picture does not
propagate and the quantization step size is controlled
to be relatively larger. B picture requires one quarter
the data of an I picture.
Temporal coding is achieved by creating three types
of pictures.
 I(Intra) Picture
 P(predictive) Picture
 B(Bi-directionally predictive) Picture
I (Intra) Picture
This type of picture is intra frame coded that need no
additional information for decoding
They require a lot of data compared to other pictures
types, and therefore they are not transmitted more
frequently than necessary. They consist primarily of
transform co-efficient and have no vectors.
The I pictures are inserted periodically for the
purpose of blocking propagation of errors caused by
inter frame coding and for the purpose of realizing
random access in broadcasting or storage media
environments. The I picture affects the total image
quality substantially.
P (predictive) Picture
This type of pictures are forward predicted from an
earlier picture which could be an I picture or P
picture. Picture data consists of vectors describing
where, in the previous picture each macro block
should be taken form and transform coefficients
which describe the correction in difference data
which must be added to that macroblock. The picture
propagates coding errors to the following P and B
pictures so it need to be quantized more finally than B
pictures.
B (Bi-directionally predictive) Picture
B pictures are bi-directionally predicted from earlier
or later I or P pictures.
B data consist of vectors describing where in earlier
or later pictures data should be taken from. It also
contains the transform coefficients that provide the
II.5 MPEG video compression Algorithms
MPEG-2 video compression algorithm is composed
of ME/MC. DCT scaler quantization. RLC and
Huffman coding functions.
It is a hybrid algorithm that combines the intra frame
and inter frame coding schemes.
The MPEG-2 video syntax has a hierarchical
structure comprising the sequence layer, groups of
picture (GOP) layer, picture layer, slice layer inacro
block layer, and block layer.
Among these the GDP layer is designed for random
access and recovery from transmission errors. The
slice layer is for resynchronization at the decoder in
the case of transmission errors.
When a slice is lost at the decoder due to transmission
errors in the channel. The next slice can be received
after resynchronization at the start of the slice. When
the decoder is turned on during the transmission of
the bit stream or when a channel change occurs in the
broadcasting environment. The pictures are
reconstructed and presented from the next I picture.
II.5.1 MPEG-1
It was finalized in 1991, and was originally optimized
to work at video resolutions of 352 x 240 pixels at
30 frames/sec for NTSC and 352 x 288 pixels at 25
frames/sec for PAL, commonly referred to as source
input format video. It is often mistakenly thought that
the MPEG-1 resolutions is limited to the above seize,
but it in fact may go as high as 4095 x 4095 at 60
frames/sec.. The bit rate is optimized for applications
of around 1.5Mb/sec, but again can be used at higher
rate if required.
MPEG-1 is defined for progressive frames only,
and has no direct provision for interlaced video
applications, such as in broadcast television
application.
II.5.2 MPEG-2
It was finalized in 1994, and addressed issues directly
related to digital television broadcasting such as the
efficient coding of field- interlaced video and
scalability. Also the target Bit rate was raised
between 4 and 9 Mb/sec, resulting in potentially very
high quality video.
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MPEG-2 consists of profiles and level. The profile
defines the bit stream scalability and the colour space
resolution, while the level defines the image
resolution and maximum bit-rate per profile. Probably
the most common descriptor in use currently is Main
Profile, Main Level (MP@ML)which refers to 720 x
480 resolution video at 30 frames/sec, at bit-rate up to
15Mb/sec for NTSC video. Another example is
HDTV resolution of 1920 x 1080 pixels at 30
frame/sec at a bit rate up to 80 Mb/sec. This is an
example of the Main Profile, High level (MP@HL)
descriptor.
MPEG
compression
dramatically
decreases the amount storage space required to record
motion picture sequences by eliminating redundant
and non essential image information from the stored
data. Less total bits means that motion pictures can be
transferred more rapidly, so rapidly in fact, that slow,
but inexpensive, communication line and storage
devices have entirely new moving picture
applications.
The human eye is forgiving of approximation and
outright elimination of the finest details in images.
This is fortunate because there is proportionally a lot
more fine detail than coarse detail in images. MPEG
compression approximates the intensity of fine detail
with just a few shades (and progressively more shades
for coarser detail) saving many bits over full
representation. The eye also sees less colour change
per inch then it does brightness variation. MPEG
compression exploits this reduction by elimination
non-essential colour detail that the human eye tends
to gloss over anyway.
II.4.4 Precaution with compression techniques
The transmission systems using compressed data must
incorporate more powerful error correction strategies
and avoid compression techniques which are
notoriously sensitive.
If not necessary compression should not be used. If
compression is to used, the degree of compression
should be as small as possible. In other words highest
practical bit rate should be used.
Low bit rate coders should only be used for the final
delivery of post produced signal to the end user.
Compression quality should only be assessed
subjectively. Compression quality varies widely with
source material. One should be careful about
demonstration which may use selected material to
achieve low bit rates. While assessing the
performance of a codec one should not hesitate in
criticizing artifacts. Eyes and ears are good to assess
the quality of the output of the codec.
Use still frames to distinguish special artifacts from
temporal artifacts, while assessing the performance.
Digital television has several advantages over
traditional TV, the most significant being use of a
smaller channel bandwidth. This frees up space for
more digital channels, other non-television services
such as pay-multimedia services and the generation of
revenue from the sales of frequency spectrum taken
by analog TV. Using Motion Picture compression
technique like MPEG, the difference picture is
produced by subtracting every pixel in one picture
from the same pixel in the next picture. MPEG-1 and
MPEG-2 standards are similar in basic concepts.
They both are based on motion compensated block
based transform coding techniques, while MPEG-4
deviates from these more traditional approaches in its
usage of software image construct descriptors, for
target bit-rate in the very low range
IV REFERENCES
[1]. Digital Audio Visual Council
http://www.davic.org/
[2]. Basic Television & Video System By Grob
and Herndon, McGraw hill publication
[3]. Real-Time Video Compression techniques
and algorithms by Raymond Westwater
Borko Furht,
[4]. Kluwer Academic Publishers
[5]. Phil tudor “Progressive transmission of
interlaced picture ”BBC research and
development
[6]. J o Drewary “Interlaced and MPEG can
motion compensation help?” British
broadcasting communication, U .K.
[7]. KEESMAN, G. et al., 1996. Trans coding of
MPEG bit streams. Image Communication
vol. 8, September, pp. 481-500. TUDOR, P.
and WERNER, O., 1997. Real-time trans
coding of MPEG-2 video bit streams.
International Broadcasting Convention,
Amsterdam, September, pp. 226-301.
[8]. THOMAS, G. and DANCER, S., 1995.
Improved motion estimation for MPEG
coding within the RACE 'COUGAR' project.
IBC, Amsterdam, September, pp. 238-243.
[9]. KNEE, M., BRIGHTWELL, P., TUDOR, P.
and WELLS, N., 1997. MPEG-2 Main
Profile coding – towards the quality limits.
International Broadcasting Convention,
Amsterdam, September.
[10]. STOREY, R., ALVES, A. et al., 1997. The
ATLANTIC News Studio: reference model
and field trial. Paper published at ECMAST,
Milan, 21-23 May.
[11]. SARGINSON,
P.,
1997.
Dynamic
multiplexing of MPEG-2 bit streams.
International Broadcasting Convention,
Amsterdam, September, pp. 566-571.
III CONCLUSIONS
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