Video Compression - Essay Example

of Faculty of Video Compression Prepared By: 2008 Contents I. Introduction 3 2. Video Compression Definition: 4 3. The Need for Video Compression 5 4. Video Compression Standards and Techniques 6 5. Problems with Digital Video 11 6. Conclusion and Future Directions 13 Bibliography 15 I. Introduction With the evolution of consumer electronic products, everything became digital audio, telephone, video, photography, newspapers..etc. So, the question -as mentioned by Alain Bouffioux (2006)- is not if a selected product will become a digital one; the question is when this product going to be digital' And how' New products already combine the three domains consumer/computer/communication (e.g. New GSM devices - Television on mobile). And the main challenge is that the lifetime of products became shorter than ever before. Due to this progressive convergence in consumer/computer/communication domains and the increasing demand to incorporate video data into telecommunications services, the corporate environment, the entertainment industry, and even at home; Digital Video Technology now became a necessity. But, the challenge for this technology is how to reduce image and digital video data rates. This concise report gives an overview on the main features of video compression and different techniques used in this technology. And due to the rapid changes in this technology, online resources were the best choice for the content of this report. The report starts with video compression definitions, the report justifies the need for video compression. Then, gives a quick overview of the main standards used in video compression and a comparison of techniques used in this technology followed by factors to choose from different techniques. And in order to realize the fact of video today the report listed some of the problems with digital video. Finally, the report gives a conclusion and presents some future directions for the video compression technology. 2. Video Compression Definition: Jim Duber once said, "The best description of compression is the one that said "Compression" is like making orange juice concentrate. Fresh oranges go in one end and concentrate comes out the other. The concentrated orange juice takes up less space, is easier to distribute, and so forth. There are different brands and types of concentrate to meet the consumers' needs or desires. Likewise, video compression takes a large file and makes it smaller. The smaller files require less hard disk space, less memory to run, and less bandwidth to play over networks or the Internet. Many compression schemes exist and have their specific strengths and weaknesses. According to Video/Imaging DesignLine "Video compression algorithms" ("codecs") manipulate video signals to dramatically reduce the storage and bandwidth required while maximizing perceived video quality. Understanding the operation of video codecs is essential for developers of embedded systems, processors, and tools targeting video applications. For example, understanding video codecs' processing and memory demands is key to processor selection and software optimization. There are other definitions for video compression. For example, TechEncyclopedia refers to "Video Compression" as "encoding digital video to take up less storage space and transmission bandwidth.". And Encyclopedian mentioned that Video compression "deals with the compression of visual video data. Video compression is necessary for efficient coding of video data in video file formats and streaming video formats." The majority of online computing dictionaries define video compression as "Compression of sequences of images. Video compression algorithms use the fact that there are usually only small changes from one "frame" to the next so they only need to encode the starting frame and a sequence of differences between frames. This is known as "inter-frame coding" or "3D coding". 3. The Need for Video Compression Video takes up a lot of space. So, Compression is needed to simply reduce the amount of space that video would otherwise take to store. Digital video compression techniques (L. Hanzo, P. J. Cherriman & J. Streit, 2007) have played an important role in the world of wireless telecommunication and multimedia systems, where bandwidth is a valuable commodity. Hence, the employment of video compression techniques is of prime importance in order to reduce the amount of information that has to be transmitted to adequately represent a picture sequence without impairing its subjective quality, as judged by human viewers. In order to understand the need for video compression more, we have a look on the advantages of video compression. The advantages of video and image compression for conservation of network bandwidth are well known. One of the big advantages of digital video is that it can be compressed for reduced bandwidth applications including transmission over satellite, cable TV and Internet-based networks. Compressed video is particularly useful for reducing storage requirements, especially in the broadcast and government markets. (Larry Maki, SBS Technologies) Compared to traditional analogue video, digital video provides advantages (Shanawaz A. Basith, Stephen R. Done, 1996) such as: no copy from copy loss, picture does not get fuzzy. signal-to-Noise ratio goes down slowly, and retrieval of editing, storage and is simpler, quicker and cheaper. 4. Video Compression Standards and Techniques 4.1 Video Compression Standards Overview During the '80s and '90s, new compression algorithms and international standards were developed to alleviate storage and bandwidth limitations imposed by digital still image and motion video applications. Today there are three standards that are widely used and accepted worldwide: JPEG (Joint Photographic Experts Group), H.261 (Video codec for audiovisual services), and 'MPEG (Motion Picture Experts Group). Each of these standards is suited for particular applications: JPEG for still image compression, H.261 for video conferencing, and MPEG for high-quality, multimedia systems (Array Microsystems, Inc. 1997). One thing they all have in common is that they are all International Standards set by the ISO (International Organization for Standardization) and IEC (International Electrotechnical Commission) - with contributors from the US, Europe and Japan among others. They are also recommendations proposed by the ITU (International Telecommunication Union). (Axis White Paper, 2002) 4.2 Video Compression Techniques This section provides a comparison for the most known techniques or standards of video compression based on detailed explanation made by Larry Maki (2005) and Axis White Paper (2002). Table (1)*: Video Compression Techniques Comparison No. Standard/Technique Definition Advantages Disadvantages 1. JPEG The most widespread picture compression format of today. Offers the flexibility to either select high picture quality with fairly high compression ratio or to get a very high compression ratio. Low complexity of the technique Lower picture quality 2. Motion JPEG A digital video sequence can be represented as a series of JPEG pictures. Flexibility both in terms of quality and compression ratio. Only uses a series of still pictures it makes no use of video compression techniques. A slightly lower compression ratio for video sequences compared to "real" video compression techniques. 3. JPEG 2000 Recently, the successor to the successful JPEG compression standard has seen the light of day. The basis was to Incorporate new advances in picture compression research into an international standard. Blockiness of JPEG is removed, but replaced with a more overall fuzzy picture. Higher compression ratio than JPEG Produces pictures typically about 25% the size of JPEG at equal picture quality. image can be stored more efficiently than pixel blocks using wavelet compression. Low latency compared to MPEG streams. For DVR applications, every image is self-contained and complete; there is no need to reconstitute frames. More complex compression technique and requires more computing power for decoding Only the most important information is used to convey the essentials of the image and much of the detail is lost, lowering the dynamic range of an image. Lower compression ratios than MPEG algorithms. 4. Motion JPEG 2000 Can also be used to represent a video sequence. Advantages are equal to JPEG 2000, i.e., a slightly better compression ratio compared to JPEG. More complexity than JPEG 2000 It doesn't take any advantages of the video sequence compression. Lower compression ration compared to real video compression techniques. 5. H.261/H.263 The H.261 and H.263 are not International Standards but only Recommendations of the ITU. Both based on the same technique as the MPEG standards (simplified versions of MPEG video compression). Originally designed for video-conferencing over telephone lines. Low bandwidth. Lack some of the more advanced MPEG techniques to really provide efficient bandwidth use. H.261/H.263 are not suitable for usage in general digital video coding. 6. MPEG-1 The first public lossy standard of the MPEG committee was the MPEG-1, ISO/IEC 11172 Based upon the same technique that is used in JPEG. Only new parts of the video sequence are included together with information of the moving parts. Still in use today for CD-ROM video compression and as part of early Windows Media players. Includes techniques for efficient coding of a video sequence. The focus is on compression ratio rather than picture quality. It can be considered as traditional VCR quality but digital instead 7. MPEG-2 MPEG-2, ISO/IEC 13818 Extends the compression technique of MPEG-1 to cover larger pictures and higher quality at the expense of a lower compression ratio and therefore also higher bandwidth usage. DVD movies are compressed using the techniques of MPEG-2. Provides more advanced techniques to enhance the video quality at the same bit-rate. The need for far more complex equipment. Are not suitable for use in real-time surveillance applications. 8. MPEG-4 MPEG-4, ISO/IEC 14496, the third generation of MPEG having the same technique. The making of studio movies is one such an example. Support of lower bandwidth consuming applications, e.g. mobile units, and on the other hand applications with extremely high quality and almost unlimited bandwidth. Most of the differences between MPEG-2 and MPEG-4 are features not related to video coding and therefore not related to surveillance applications. * Based on detailed explanation made by Larry Maki (2005) and Axis White Paper (2002). 4.3 Factors of choosing compression techniques: Listed below many factors to be considered when choosing a compression technique presented by Shanawaz A. Basith and Stephen R. Done. Real-Time / Non-Real-Time: To have sufficient frame rate (frames per second) to make sure that there is no jerky motion. Symmetrical / Asymmetrical: Symmetrical implies capturing, storing, and playback at the same rate. Asymmetrical uses more time to compress and hence may have an advantage for playback speed. Compression Ratio: Generally the higher the compression ratio the poorer the video quality. Lossless / Lossy: The loss factor determines whether there is a loss of quality between the original image and the image after it has been compressed and played back (decompressed). Inter-frame / Intra-frame: Inter-frame compresses each frame of the sequence as a discrete picture. Intra-frame is a more powerful method, which uses a predictive technique. 5. Problems with Digital Video These problems, which include distortions that get added to a video signal during digital encoding, are known as artifacts. Shanawaz A. Basith and Stephen R. Done presented several types of artifact. This section of the report will present some of the various artifacts, may caused by general problem, by compression, or during implementation. Aliasing: Aliasing occurs when a signal being sampled contains frequencies that are too high to be successfully digitised at a given sampling frequency. Quantisation Noise: This form of distortion occurs. It is the coarseness of these levels that causes quantisation noise. Overload: Like quantisation noise, If a signal is digitised that is too high in amplitude, then the picture will appear bleached. Digital Signal Degradation: Due to the compression techniques used, a single bit error in the data stream could for example cause a large block of pixels to be displayed in a completely different colour to that intended. The Gibbs Effect: This is most noticeable around artificial objects (plain coloured, large text and geometric). It shows up as a blurring or haze around the object, where the sudden transition is made from the artificial object to the background. Blockiness: Another artifact that affects JPEG and MPEG is blockiness. When video footage involving high speed motion is digitised, the individual 8x8 blocks that make up the picture become more pronounced. Lossy Compression: Due to higher compression ratios produced by a lossy compression method some of the information contained in the signal, may be removed. Implementation problems: Both encoding and decoding of video information requires a significant amount of processing power. In general though, the encoding is far more demanding. 6. Conclusion and Future Directions The world as we see it through video is about to change. Digital video technology has become a necessity due to the increasing demand to include video data for personal use as well as in the entertainment industry, the corporate world, the government and defense. Video compression is gaining popularity due to evolution in consumer electronic products and since storage requirements and bandwidth requirements are reduced with compression. Due to its simplicity, Motion JPEG is a good choice for use in many applications. It ensures inexpensive equipment at the cost of slightly higher bandwidth consumption. For more efficient bandwidth usage, some of the true motion picture compression standards are preferred. MPEG-1 can be more effective than MJPEG. However, at a slightly higher cost, MPEG-2 offers some advantages that provide better image quality -- comprising of frame rate and resolution -- but requires more network bandwidth consumption. It is also a more complex technique. MPEG-4 is developed to offer a compression technique for applications demanding less image quality and bandwidth. It is also able to deliver video compression similar to MPEG-1 and MPEG-2, with higher image quality and higher bandwidth consumption. Since the H.261/H.263 recommendations are neither international standards nor offers any compression enhancements compared to MPEG, they are not of any real interest. (Axis, 2002) The MPEG committee for example continues to add video and graphics standards, such as MPEG-7 and MPEG-21, to their standards efforts. So, over time, compression rates and the quality of data will continue to improve, providing more efficient use of bandwidth, storage and computing resources. Nicholas Carlson (2006) mentioned some future direction such as: Video Conferences call and on-demand video on mobiles: Mobile phones have screens, speakers and microphones. They can take pictures and record video. And they can connect to the Internet. So why can't a video conference call be made from a mobile phone' For the same reason on-demand video doesn't really work on mobile devices. And for the same reason you can only watch eight HDTV channels at home. Closing the Distance of Bandwidth: Most mobile devices connect to the Internet at about 10KB per second. Video requires a bandwidth of at least 50KB per second. That's where video-compression technology currently stands, according to Deepak Turaga, video-compression researcher at IBM's T.J. Watson Research Center. The distance between 10KB and 50KB is far, but it's a distance that could be closed. Object Versus Blocks (integration of object-based compression): To achieve this, block-based video compression has to be overcome. Block-based compression works by segmenting the video into rows and columns that form blocks, which are the large pixels in streaming video over the Internet. The trouble with object-based compression is that it requires modeling all the objects that might appear in the video. Bibliography 1. Axis communications 2002. Compression Techniques. http://www.axis.com/documentation/whitepaper/video/videocompression.pdf 2. Berkeley Design Technology, Inc 2006. Introduction to video compression http://www.videsignline.com/howto/showArticle.jhtml'articleID=185301351 3. Bouffioux, Alain 2006. Audio/Video compression: An introduction http://www.montefiore.ulg.ac.be/services/acous/STSI/file/1.%20AV%20compression%20-%20Introduction%20-%20Dec06.ppt 4. Carlson, Nicholas 2006. Video Compression And The Future. Internews.com http://www.internetnews.com/infra/article.php/3599551 5. Dave Marshall 2001. Video Compression, Cardiff University http://www.cs.cf.ac.uk/Dave/Multimedia/node245.html 6. Duber, Jim. FireWire and Creating Web-Based Video Content, University of California http://www-writing.berkeley.edu/tesl-ej/ej14/int.html 7. Maki, Larry. Video Compression Standards, Cotsjournalonline, June 2005 http://www.cotsjournalonline.com/home/article.php'id=100349 8. L. Hanzo, P. J. Cherriman & J. Streit 2007. Video Compression and Communications: From Basics to H.261, H.263, H.264, MPEG2, MPEG4 for DVB and HSDPA-Style Adaptive Turbo-Transceivers, Second Edition, John Wiley & Sons, Ltd. P.1 http://eprints.ecs.soton.ac.uk/14583/1/video-book-2e-sample-chaps.pdf 9. Shanawaz A. Basith & Stephen R Done 1996 Digital Video, MPEG and Associated Artifacts Departments of Computing & Electrical Engineering Imperial College London http://www.doc.ic.ac.uk/'nd/surprise_96/journal/vol4/sab/report.html Online Dictionaries: TechEncyclopedia. http://www.techweb.com/encyclopedia/defineterm.jhtml;jsessionid=Z3X1BES5050T4QSNDLPSKHSCJUNN2JVN'term=video+compression Encyclopedian http://www.encyclopedian.com/vi/Video-compression.html Free online dictionary of computing. http://onlinedictionary.datasegment.com/word/video%20compression Best Online Dictionary http://www.bestonlinedictionary.com/computer-terms-dictionary/computer-dictionary-v/definition-video+compression.htm Define the net http://www.definethat.com/define/7120.htm 10. Video Compression. Array Microsystems, Inc., 1997 http://www.dip.ee.uct.ac.za/'nicolls/lectures/eee401f/projects/compres.pdf Read More