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- 1. SEMINAR on MULTIMEDIA & APPLICATIONS – MCA 0422 Digital Video & Image Compression By, T.S.V. ARUNPRASAD 15 MCA 12
- 2. Digital Video: ***************** Digital video is a representation of moving visual images in the form of encoded digital data. Digital video refers to the capturing, manipulation and storage of moving images that can be displaced on computer screens. This requires that the moving images be digitally handled by the computer. Digital video was first introduced commercially in 1986 with the Sony D1 format.
- 3. IMAGE: ********* A digital image is a numeric representation of a two-dimensional image. Depending on whether the image resolution is fixed, it may be of vector or raster type. By itself, the term "digital image" usually refers to raster images or bitmapped images. Digital images are made of picture elements called pixels.
- 4. How much Compression? Compression performance is often specified by giving the ratio of input data to output data for the compression process. This measure is a dangerous one unless you are careful to specify the input data format in a way that is truly comparable to the output data format. A much better way to specify the amount of compression is to determine the number of bits per displayed pixel needed in the compressed bit stream.
- 5. How Good Is The Picture? In talking about picture quality performance of a compression system, it is helpful to divide the world of compression into two parts – lossless compression and lossy compression. Lossless compression means that the reproduced image is not changed in any way by the compression or decompression process. We do not have to worry about the picture quality for a lossless system. On the other hand, lossy compression systems by definition do make some change to the image – something is different. Lossy compression systems may introduce any of the digital video artifacts, or they may even create some unique artifacts of their own.
- 6. DATA COMPRESSION: ************************* Data compression is defined as the process of encoding data using a representation that reduces the overall size of data. This reduction is possible when the original dataset contains some type of redundancy. Digital image compression is a field that studies methods for reducing the total number of bits required to represent an image. This can be achieved by eliminating various types of redundancy that exist in the pixel values.
- 7. Lossy Compression Method: ********************************* Original Image Transform Quantization Entropy Coding De - Quantization Inverse Transform Restored Image Entropy Decoding Channel Compressor Decompressor
- 8. Quantization: ***************** Quantization is a many-to-one mapping that replaces a set of values with only one representative value. Scalar and vector quantization are two basic types of quantization. SQ (scalar quantization) performs many-to-one mapping on each value. VQ (vector quantization) replaces each block of input pixels with the index of a vector in the codebook, which is close to the input vector by using some closeness measurements.
- 10. Entropy Coding: ******************* Entropy represents the minimum size of dataset necessary to convey a particular amount of information. Huffman coding, LZ (Lempel-Ziv) coding and arithmetic coding are the commonly used entropy coding schemes.
- 11. Why Compressed? The reason is that the correlation between one pixel and its neighbor pixels is very high, or we can say that the values of one pixel and its adjacent pixels are very similar. This is called the intraframe correlation in video compression because it is the correlation in a single frame. Once the correlation between the pixels is reduced, we can reduce the storage quantity. The image compression method is also applied to compression video.
- 12. Video Compression Technique: ************************************* Simple Compression Techniques: A good example of simple compression is truncation – reducing data through arbitrary lowering of the bits per pixel. If we go too far with truncation, we will begin to see contouring and our image will start looking like a cartoon. Another simple compression scheme, which creates a different kind of artifact, is the color lookup table (CLUT) approach. A third simple technique is run – length (RL) coding. In this technique, blocks of repeated pixels are replaced with a single value and a count of how many times to repeat that value.
- 13. Transform Coding Technique: A transform is a process that converts a bundle of data into an alternate form which is more convenient for some particular purpose. Transforms are ordinarily designed to be reversible – that is, there exists an inverse transform which can restore the original data. In video compression, a “bundle of data” is a group of pixels – usually a two-dimensional array of pixels from an alternate from an image, for example, 8 x 8 pixels. Transformation is done to create an alternate form which can be transmitted or stored using less data. At decompression time, the inverse transform is run on the data to reproduce the original pixel information.
- 14. References: *************** Websites: http://www.edb.utexas.edu/minliu/multimedia/Digital%20Video.pdf https://books.google.co.in/books?id=7uKvi3Oyqs0C&pg=PA57&lpg=PA57&dq=multimedia+systems+by+john+f.+koegel +buford+chapter+6&source=bl&ots=hEP97zqQIY&sig=eE77SVIUtIvcQi3jqhBC64kZSsw&hl=en&sa=X&ved=0ahUKEwjn7Zi gzqPSAhXCtpQKHfLvDkkQ6AEIHzAB#v=onepage&q=multimedia%20systems%20by%20john%20f.%20koegel%20buford%20 chapter%206&f=false https://en.wikipedia.org/wiki/Digital_video https://en.wikipedia.org/wiki/Digital_image http://digital.cs.usu.edu/~xqi/Proposal/Chapter2.pdf http://disp.ee.ntu.edu.tw/meeting/%E7%B6%AD%E6%AF%85/Digital%20Video%20Compression%20Fundamentals%20an d%20Standards/Digital%20Video%20Compression%20Fundamentals%20and%20Standards.pdf Book: Multimedia Systems - John F. Koegel Buford.