simple video compression

MULTIMEDIA PRESENTATION

VIDEO COMPRESSION

PROJECT MEMBERS

LALIT DUBEY

VIDEO

Refers to recording, manipulating, and displaying moving images, especially in a format that can be presented on a television.

Refers to displaying images and text on a computer monitor. The video adapter, for example, is responsible for sending signals to the display device.

MORE ABOUT VIDEO

• Video is a stream of data composed of discrete frames,containing both audio and pictures• Continuous motion produced at a frame rate of 15 fps orhigher• Traditional movies run at 24 fps

• TV standard in USA (NTSC) uses ≈ 30 fps

With digital video, four factors have to be kept in mind.

# Frame rate

# Colour Resolution

# Spatial Resolution

# Image Quality

Frame RateThe standard for displaying any type of non-film video is 30 frames per second (film is 24 frames

per second). Additionally these frames are split in half (odd lines and even lines), to form what

are called fields.

When a television set displays its analogue video signal, it displays the odd lines (the odd field)

first. Then is displays the even lines (the even field).

Each pair forms a frame and there are 60 of these fields displayed every second (or 30 frames

per second). This is referred to as interlaced video.

Fragment of the "matrix" sequence (2

frames)

After processing the fragment on the left by the FRC filter the

frame rate increased 4 times

Colour Resolution

This second factor is a bit more complex. Colour resolution refers to the number of colours displayed on the screen at one time. Computers deal with colour in an RGB (red-green-blue) format, while video uses a variety of formats. One of the most common video formats is called YUV.

This test table was used to estimate the color

resolution. First we determine the border

when one of the colors on the resolution chart

disappears, and color sharpness is found on

the scale on the right.

Spatial ResolutionThe third factor is spatial resolution - or in other words, "How big is the picture?".

Since PC and Macintosh computers generally have resolutions in excess of 640 by

480,

The National Television Standards Committee ( NTSC) standard used in North

America and Japanese Television uses a 768 by 484 display.

The Phase Alternative system (PAL) standard for European television is slightly

larger at 768 by 576.

Spatial resolution is a parameter that

shows how many pixels are used to

represent a real object in digital form. Fig.

2 shows the same color image represented

by different spatial resolution. Left flower

have a much better resolution that right

one

Image qualityThe final objective is video that looks acceptable for your application.

For some this may be 1/4 screen, 15 frames per second (fps), at 8 bits per pixel.

Other require a full screen (768 by 484), full frame rate video, at 24 bits per pixel (16.7 million colours).

MORE DEFINTION OF VIDEO

.

• VIDEOS OR MOVIES ARE COMBINATION OF SOUND AND IMAGES, INSTEAD OF SINGLE PICTURE MOVIES ARE COMPOSED OF SEREIS OF PICTURES WHICH ARE SHOWED ONE AFTER ANOTHER AT A CERTAIN SPEED WITH SOUND PLAYED IN BACKGROUN.

• A FAMOUS PHRASE “ A MOVIE OR VIDEO MUST BE WORTH A MILLION WORDS”.

??????

AS DEFINITIONS INDICATES A VIDEO IS SEQUENCE OF FRAME OF IMAGES

AND A NORMAL SINGLE IMAGE OCCUPY 2MB OF MEMORY SPACE IN MEMORIES THEN A VIDEO CONTAIN

HOW MUCH????

Storage of normal elements

• 2 MBAPPROXA SINGLE IMAGE OCCUPY ABOUT

• 10-15 MBAPPROXA 1 MINUTE AUDIO OCCUPY ABOUT

• 2 GBAPPROXA 1 MINUTE VIDEO

OCCUPY ABOUT

Problem

FILES LIKE IMAGE, AUDIO AND VIDEO TAKE LOT OF DISK SPACE, WITH MULTIPLE SUCH MEDIA FILES INCREASE COST.

SUCH FILES REQUIRE A LARGE DATA TRANSFER RATE THAT MAY BE BEYOND THE CAPABILITES OF BOTH THE PROCESSOR AND DISK.

solution

DUE TO THIS FACT IT IS EXPECTED TO FUCUS THE MEDIA FILES TO A PROCESS CALLED

COMPRESSION.

What is compression???

Compression is the process used to reduce the file sizes using mathematical algorithms after which it become much easier to manipulate these files.

More about compression

The amount of compression which can be achieve depends both on the original media data as well as the compression technique applied.

Different compression methods

MPEG COMPRESSION:MPEG

MPEG 2

MPEG 3

MPEG 4

MPEG 7

H.261 (Px64)

H.263 Standard

MPEG Compression

• Compression through

–Spatial

–Temporal

Spatial Redundancy

• Take advantage of similarity among most neighboring pixels

Spatial Redundancy Reduction• RGB to YUV

– less information required for YUV (humans less sensitive to chrominance)

• Macro Blocks– Take groups of pixels (16x16)

• Discrete Cosine Transformation (DCT)– Based on Fourier analysis where represent signal as sum of sine's

and cosine’s– Concentrates on higher-frequency values– Represent pixels in blocks with fewer numbers

• Quantization– Reduce data required for co-efficients

• Entropy coding– Compress

Loss of Resolution

Original (63 kb)

Low (7kb)

Very Low (4 kb)

Temporal Redundancy

• Take advantage of similarity between successive frames

950 951 952

Temporal Activity

“Talking Head”

Temporal Redundancy Reduction

Temporal Redundancy Reduction

• I frames are independently encoded

• P frames are based on previous I, P frames

– Can send motion vector plus changes

• B frames are based on previous and following I and P frames

– In case something is uncovered

Typical MPEG Parameters

MPEG (Moving Picture Expert Group)

MPEG was set standard for Audio and Video compression and transmission

MPEG-1 is a standard for lossy compression of video and audio. It is designed to

compress VHS-quality raw digital video and CD audio down to 1.5 Mbit/s (26:1

and 6:1 compression ratios respectively) without excessive quality loss, making

Video CDs, digital cable/satellite TV and digital audio broadcasting (DAB) possible.

MPEG-1 has become the most widely compatible lossy audio/video format in the

world, and is used in a large number of products and technologies.

The best-known part of the MPEG-1 standard is the MP3 audio format .

The standard consists of the following five Parts:

1. Systems (storage and synchronization of video, audio, and other data together)

2. Video (compressed video content)

3. Audio (compressed audio content)

4. Conformance testing & 5. reference software

MPEG-2•was designed for coding interlaced images at transmission rates

above 4 million bits per second.

•MPEG 2 can be used on HD-DVD and blue ray disc.

•handles 5 audio channels,

•Covers wider range of frame sizes (HDTV).

•Provides resolution 720*480 and 1280*720 at 60 fps with full CD

quality audio used by DVD-ROM.

•MPEG-2 can compress 2 hours video into a few GHz.

•MPEG-2 is used for digital TV broadcast and DVD.

• An MPEG-2 is designed to offer higher quality than MPEG-1, at a

higher bandwidth (between 4 and 10 Mbit/s).

•The scheme is very similar to MPEG-1, and scalable.

MPEG-3

Designed to handle HDTV signal in range 20 to 40 Mbits/sec.

HDTV-resolution is 1920* 1080*30 Hz

But MPEG-2 was fully capable of handling HDTV so MPEG -3 is no longer mentioned.

MPEG-4MPEG-4 is a collection of methods defining compression of audio and

visual (AV) digital data.

MPEG-4 absorbs many of the features of MPEG-1 and MPEG-2 and

other related standards, Wavelength band MPEG-4 files are smaller

than JPEG. so they transmit video and images over narrower

bandwidth and can mix video with text graphics and 2D and 3D

animation layers.

MPEG-4 provides a series of technolgies for developers for various

service providers and end users.

SP use for data transparency

Helps end users with wide range of interaction with animated objects.

MPEG-4 multiplexes and synchronizes data .

Interaction with audio visual scene.

MPEG-7MPEG-7 is a content representation standard for information search.

It is also titled Multimedia Content Description Interface.

It will define the manner in which audiovisual materials can be coded and classified

so the materials can be easily located using search engines just as search engines are

used to locate text-based information

. Music, art, line drawings, photos, and videos are examples of the kinds of materials

that will become searchable based on descriptive language defined by MPEG-7.

* Provide a fast and efficient searching, filtering and content identification

method.

* Describe main issues about the content (low-level characteristics, structure,

models, collections, etc.).

* Index a big range of applications.

* Audiovisual information that MPEG-7 deals is : Audio, voice, video, images,

graphs and 3D models

* Inform about how objects are combined in a scene.

* Independence between description and the information itself.

MPEG-7 applications

* Digital library: Image/video catalogue, musical

dictionary.

* Multimedia directory services: e.g. yellow pages.

* Broadcast media selection: Radio channel, TV channel.

* Multimedia editing: Personalized electronic news service,

media authoring.

* Security services: Traffic control, production chains...

* E-business: Searching process of products.

* Cultural services: Art-galleries, museums...

* Educational applications.

* Biomedical applications.

Still Image Compression - JPEG

• Defined by Joint Photographic Experts Group• Released as an ISO standard for still color and gray-scaleimages• Provides four modes of operation:— Sequential (each pixel is traversed only once)— progressive (image gets progressively sharper)— Hierarchical (image compressed to multipleresolutions)— lossless (full detail at selected resolution)

Definitions in the JPEG StandardThree levels of definition:• Baseline system (every codec must implement it)• Extended system (methods to extend the baseline system)• Special lossless function (ensures lossless compression/decompression)

H.261 (Px64)

• H.261 was designed for datarates which are multiples of64Kbit/s, and is sometimes called p x 64Kbit/s (p is in therange 1-30).•These datarates suit ISDN lines, for which this video codecwas designed for• Intended for videophone and video conferencing systems

H.263 Standard

•The development of modems allowing transmission in therange of 28-33 kbps paved the way for the development of animproved version of H.261• It was designed for low bitrate communication , however thislimitationhas now been removed• It is expected that H.263 will replace H.261

ADVANTAGES

- Occupies less disk space.

- Reading and writing is faster.

- File transferring is faster.

- The order of bytes is independent.

DISADVANTAGES

- Compilation need to be done again for compression.

- Errors may occur while transmitting data.

- The byte / pixel relationship is unknown

- Has to decompress the previous data.

THANKS FOR WATHCHING…