Modern University For Technology & Information Faculty of Computer Science CS 371 Multimedia Prof. Dr. \ Alaa Abd El-Rahim 2018 Fall CS 371Multimedia Final Review Sheet Question Discuss the different image formats: TIF, JPG, PNG, and EXIF. - - BMP, Bit Map - Developed by Microsoft. A bit-map representation stores the graphic/image data in the same manner that the computer monitor contents are stored in video memory (Video Card). JPEG (JPG), Joint Photographic Experts Group - A standard with several different image representations. The transform-based lossless compression method can create very small files. GIF, Graphic Interchange Format - Originally, developed by CompuServe, GIF uses indexed color and LZW (Lempel-Ziv Welch compression algorithm). TIFF (TIF), Tagged Image File Format - A standard with lossless compression. PNG, Portable Network Graphics - Developed as non-proprietary alternative for GIF EXIF Exchange Image File: is an image format for digital cameras. Question Explain how the dithering technique is used with the binary image to increase the gray levels. Dithering is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images. Dither is routinely used in processing of both digital audio and digital video data, and is often one of the last stages of audio production to compact disc Dithering is used for displaying monochrome images Also, For printing on a 1-bit printer, dithering is used to calculate larger patterns of dots, such that values from 0 to 255 corresponding to pleasing patterns that correctly represent darker and brighter pixel. The main strategy is to replace a pixel value by a larger pattern, say 2 x 2 or 4 x 4 , such that the number of printed dots approximates the varying sized disks of ink used in halftone printing. Half-tone printing is an analog process uses smaller or larger filled circles of black ink to represent shading, for newspaper printing say. Question Explain the multimedia authoring and describe briefly the most common three metaphors. Multimedia Authoring Multimedia authoring is the creation of multimedia productions, sometimes called “movies” or “presentations”. An Authoring System is a program which has pre-programmed elements for the development of interactive multimedia software titles. Authoring systems vary widely in orientation, capabilities, and learning curve. There is no such thing (at this time) as a completely point-and-click automated authoring system; some knowledge of heuristic thinking and algorithm design is necessary. Iconic/Flow Control: - This tends to be the speediest (in development time) authoring style; it is best suited for rapid prototyping and short-development time projects. Many of these tools are also optimized for developing Computer-Based Training (CBT). The core of the paradigm is the Icon Palette, containing the possible functions/interactions of a program, and the Flow Line, which shows the actual links between the icons. Frame: The Frame paradigm is similar to the Iconic/Flow Control paradigm in that it usually incorporates an icon palette; however, the links drawn between icons are conceptual and do not always represent the actual flow of the program. Card/Scripting: The Card/Scripting paradigm provides a great deal of power (via the incorporated scripting language) but suffers from the index-card structure. It is excellently suited for Hypertext applications, and supremely suited for navigation intensive (a la Cyan's "MYST" game) applications. Question Explain the Color Look-Up Tables (LUTs) algorithm used with the GIF image. Answer Question Calculate the image storage required for image resolution 640 X 480 for the following image types: Binary Image, True Gray-Level Image, GIF Color Image, BMP Color Image. The Binary image each pixel store in one bit, so the image resolution 640 X 480 required Storage size = 640 X 480 = 307200 Bits = 640 X 480 / 8 = 38400 Bytes = 640 X 480 / (8 * 1024) = 37.5 KB The True Gray image each pixel store in one byte, so the image resolution 640 X 480 required Storage size = 640 X 480 = 307200 Bytes = 640 X 480 / (1024) = 300 KB The GIF Color image each pixel store in one byte, so the image resolution 640 X 480 required Storage size = 640 X 480 = 307200 Bytes = 640 X 480 / (1024) = 300 KB The BMP Color image each pixel store in 3 bytes(24 Bits), ( pixel R G B ) , so the image resolution 640 X 480 required Storage size = 640 X 480 X 3 = 921600 Bytes = 640 X 480 / ( 1024) = 900 KB Question Discuss what is meant by the terms static media and dynamic media. Give some examples of static media and dynamic media. Static Media – does not change over time, e.g. text, graphics Dynamic Media --- Time dependent (Temporal), e.g. Video, sound, animation. Question What is meant by MIDI? How is a basic MIDI message structured? MIDI is a protocol that enables computers, synthesizers, keyboards, and other musical devices to communicate with each other. It is a set of instructions how a computer should play musical instruments. MIDI Message structure: MIDI message includes a status byte and up to two data bytes. Status byte The most significant bit of status byte is set to 1. The 4 low-order bits identify which channel it belongs to (four bits produce 16 possible channels). The 3 remaining bits identify the message. The most significant bit of data byte is set to 0. Question Explain how can MIDI be used effectively in multimedia musical applications? Multimedia Application: -Low Bandwidth/(Low Quality?) Music on Web, Quicktime etc supports Midi musical instrument set -Sound Effects --- Low Bandwidth alternative to audio samples, Sound Set part of GM sound set Control of external devices --- e.g Synchronization of Video and Audio (SMPTE), Midi System Exclusive, AUDIO RECORDERS, SAMPLERS Control of synthesis --- envelope control etc -MPEG 4 Compression control --Digital Audio Question What is the purpose of using "Chroma" sub-sampling with the digital video? Why is it feasible? Human vision has less acuity in colour vision than it has in black and white—one can distinguish close black lines more easily than colour lines, which soon are perceived just a mass without texture as the lines move close to each other. Therefore, it is acceptable perceptually to remove a good deal of colour information. In analog, this is accomplished in broadcast TV by simply assigning a smaller frequency bandwidth to colour than to black and white information. In digital, we “decimate” the colour signal by subsampling (typically, averaging nearby pixels). The purpose is to have less information to transmit or store. Question How many signals are used in S-Video? And what are the signals used in S-Video? - S-Video is used 4 signals The signals used in S-Video are : Luminance Chrominance Audio Sync Question What are the advantages of using digital video? The advantages of using digital video are: i) Video can be stored on digital devices or in memory, ready to be processed (noise removal, cut and paste, etc.), and integrated to various multimedia applications; ii) Direct access is possible, which makes nonlinear video editing achievable as a simple, rather than a complex, task; iii) Repeated recording does not degrade image quality; iv) Ease of encryption and better tolerance to channel noise. Q Discuss the audio quality versus the audio data rate. Quality Sample Rate(KHz) Telephone 8 AM Radio FM Radio 11.025 22.050 CD 44.1 DAT 48 DVD Audio 192 Bits Data Rate Mono / Frequency per (if Stereo Band Sample Uncompressed) 200-3,400 8 Mono 8 KBytes/sec Hz 8 Mono 11.0 KBytes/sec 16 Stereo 88.2 KBytes/sec 176.4 20-20,000 16 Stereo KBytes/sec Hz 192.0 20-20,000 16 Stereo KBytes/sec Hz 1,152.0 20-20,000 24 Stereo KBytes/sec Hz Question Calculate the space required for recording sound with duration of 15 minutes for the telephone conversation. The Telephone sample rate is 8 KHZ and Bits per sample is 8 Bits 8 x 103 x 8 x (15 x 60) / (8 * 2^20) = MB Question Calculate the space required for recording sound with duration of 15 minutes for the CD mono and the CD stereo. The CD sample rate is 44.1 KHz and Bits per sample is 16 Bits Mono 44.1 x 103 x 16 x (15 x 60) / (8 * 2^20) = MB Stereo (left/right) channels, the amount of Mono is doubled: x 2 = MB Question Calculate the space required for recording sound with duration of 15 minutes for The DVD mono and the DVD stereo. The DVD sample rate is 192 KHZ and Bits per sample is 24 Bits Mono 192 x 103 x 24 x (15 x 60) / (8 * 2^20) = MB Stereo (left/right) channel, the amount is doubled: x 2 = MB Question Calculate the space required for recording sound with duration of 15 minutes for the Radio FM. The Radio FM sample rate is 22.050 KHZ and Bits per sample is 16 Bits Radio FM is Stero 22.050 x 103 x 16 x (15 x 60) /(8 * 2^20) = MB Question Calculate the space required for recording sound with duration of 15 minutes for the Radio AM. Radio AM is Mono only The Radio AM sample rate is 11.025 KHZ and Bits per sample is 8 Bits 11.025 x 103 x 8 x (15 x 60) / 8 (bits) * 2^20 = MB Question Discuss the distinction between lossless and lossy compression algorithms. Lossless Compression -- where data is compressed and can be reconstituted (uncompressed) without loss of detail or information. These are referred to as bit-preserving or reversible compression systems also. Lossy Compression -- where the aim is to obtain the best possible fidelity for a given bit-rate or minimizing the bit-rate to achieve a given fidelity measure. Video and audio compression techniques are most suited to this form of compression. Question Briefly explain, the entropy coding and transform coding techniques. Illustrate your answer with a simple example of each type. ENTROPY METHODS: The entropy of an information source S is defined as: H(S) = SUMI (PI Log2 (1/PI) Where PI is the probability that symbol SI in S will occur. Log2 (1/PI) indicates the amount of information contained in SI, i.e., The number of bits needed to code SI. Question Suppose the dynamic range of speech in telephony implies ratio Vmax/Vmin of about 256. Using uniform quantization, how many bits should we use to encode speech to make the quantization noise at least an order of magnitude less than the smallest detectable telephonic sound? The Telephone sample store in 8 Bits -- 8 ^ 2 = 256 So Sound range will be 0 .. 256, We will use something like the Median Cut Algorithm but on gray scale level, as picking a value between 0 and half of the range. Pick the intensity level of gray scale most near to the rate. Q Explain how to handling the stored sampled audio (Synthetic Sounds Q Discuss the main steps in JPEG image compression. JPEG is a lossy image compression method. The effectiveness of the DCT transform coding method in JPEG relies on three major observations: Observation 1. Useful image contents change relatively slowly across the image— that is, it is unusual for intensity values to vary widely several times in a small area—for example, in an 8 × 8 image block. Spatial frequency indicates how many times pixel values change across an image block. The DCT formalizes this notion with a measure of how much the image contents change in relation to the number of cycles of a cosine wave per block. Observation 2. Psychophysical experiments suggest that humans are much less likely to notice the loss of very high-spatial frequency components than lower frequency components. JPEG’s approach to the use of DCT is basically to reduce high-frequency contents and then efficiently code the result into a bitstring Observation 3. Visual acuity (accuracy in distinguishing closely spaced lines) is much greater for gray (“black and white”) than for color. We simply cannot see much change in color if it occurs in close proximity— think of the blobby ink used in comic books. This works simply because our eye sees the black lines best, and our brain just pushes the color into place. In fact, ordinary broadcast TV makes use of this phenomenon to transmit much less color information than gray information. When the JPEG image is needed for viewing, the three compressed component images can be decoded independently and eventually combined.