Questions and Answers for Multimedia Computing Part Impu.edu.iq/images/forth_class_comp/multimedia-compressed.pdf · A Multimedia System is a system capable of processing multimedia

Questions and Answers for Multimedia Computing

Questions and Answers for

Multimedia Computing Part I

Department of Computer Techniques

Engineering

Level 4

Dr. Rasha Thabit

[email protected]

1 Dr. Rasha Thabit


Q: What is meant by the terms Multimedia and HyperMedia? Distinguish between these two concepts.

Multimedia ---- An Application which uses a collection of multiple media source e.g. text, graphics, images, sound/audio, animation and/or video. Hypermedia ---- An application which uses associative relationships among information contained within multiple media data for the purpose of facilitating access to, and manipulation of, the information encapsulated by the data. Hypermedia contrasts with the broader term multimedia, which may include non-interactive linear presentations as well as hypermedia. Q: Define HyperText and explain the traversal through hypertext. Hypertext is a text which contains links to other texts. The term was invented by Ted Nelson around 1965. Traversal through pages of hypertext is usually non-linear (as indicated below).

Q: Define HyperMedia and list 4 hypermedia applications. Hypermedia ---- An application which uses associative relationships among information contained within multiple media data for the purpose of facilitating access to, and manipulation of, the information encapsulated by the data.

• The World Wide Web (WWW). • Powerpoint. • Adobe Acrobat (or other PDF software). • Adobe Flash.

Q: What is meant by the terms static (or discrete) media and dynamic (or continuous) media? Give examples of each type of media. Static (or discrete) media: time independent media such as normal data, text, single images, and graphics. Dynamic (or continuous) media: time dependent media such as video, animation and audio. Q: Why is file or data compression necessary for Multimedia activities? Multimedia files are very large therefore for storage, file transfer etc. file sizes need to be reduced. Text and other files may also be encoded/compressed for email and other applications.

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Q: Give a definition of multimedia and multimedia system. Multimedia is the field concerned with the computer-controlled integration of text, graphics, drawings, still and moving images (Video), animation, audio, and any other media where every type of information can be represented, stored, transmitted and processed digitally. A Multimedia System is a system capable of processing multimedia data and applications. Q: What are the key distinctions between multimedia data and more conventional types of media?

• Multimedia systems deal with the generation, manipulation, storage, presentation, and communication of information in digital form.

• The data may be in a variety of formats: text, graphics, images, audio, and video. • A majority of this data is large and the different media may need synchronization -the data

may have temporal relationships as an integral property. • Some media is time independent or static or discrete media: normal data, text, single

images, graphics are examples. • Video, animation and audio are examples of continuous media which is time dependent

media. Q: What key issues or problems does a multimedia system have to deal with when handling multimedia data? The key issues multimedia systems need to deal with are:

• How to represent and store temporal information. • How to strictly maintain the temporal relationships on play back/retrieval • What processes are involved in the above? • Data has to be represented digitally – Analog/Digital Conversion, Sampling etc. • Large Data Requirements - bandwidth, storage, data compression is usually Mandatory.

Q: List the four basic characteristics of multimedia system? A Multimedia system has four basic characteristics:

• Multimedia systems must be computer controlled. • Multimedia systems are integrated. • The information they handle must be represented digitally. • The interface to the final presentation of media is usually interactive.

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Q: List some challenges that can face the multimedia systems. • Distributed Networks. • Temporal relationship between data. Render different data at same time - continuously. Sequencing within the media: playing frames in correct order/time frame in video. Synchronization: inter-media scheduling.

Q: List and explain 5 desirable features in multimedia systems. (5 points from the following are enough)

• Very High Processing Power - needed to deal with large data processing and real time delivery of media. Special hardware commonplace.

• Multimedia Capable File System - needed to deliver real-time media - e.g. Video/Audio Streaming.

• Special Hardware/Software needed - e.g. RAID technology. • Data Representations - File Formats that support multimedia should be easy to handle yet

allow for compression/ decompression in real-time. • Efficient and High I/O - input and output to the file subsystem needs to be efficient and

fast. • Special Operating System - to allow access to file system and process data efficiently and

quickly. Needs to support direct transfers to disk, real-time scheduling, fast interrupt processing, I/O streaming etc.

• Storage and Memory - large storage units and large memory. Large Caches also required and high speed buses for efficient management.

• Network Support - Client-server systems common as distributed systems. • Software Tools - user friendly tools needed to handle media, design and develop

applications, and deliver media. Q: What are the hardware and software components that are required in multimedia system? Or Q: List the components of a multimedia system.

• Capture devices: Video Camera, Video Recorder, Audio Microphone, Keyboards, mice, graphics tablets, 3D input devices, tactile sensors, VR devices. Digitizing Hardware.

• Storage Devices: Hard disks, CD-ROMs, DVD-ROM, etc. • Communication Networks: Local Networks, Intranets, Internet, Multimedia or other

special high speed networks. • Computer Systems: Multimedia Desktop machines, Workstations, MPEG/VIDEO/DSP

Hardware. • Display Devices: CD-quality speakers, HDTV, SVGA, Hi-Res monitors, Color printers

etc.

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Q: List and explain three main multimedia research topics.

• Multimedia processing and coding. This includes multimedia content analysis, content-based multimedia retrieval, multimedia security, audio / image / video processing, compression, and so on.

• Multimedia system support and networking. People look at such topics as network protocols, Internet, operating systems, servers and clients, quality of service (QoS), and databases.

• Multimedia tools, end systems, and applications. These include hypermedia systems, user interfaces, authoring systems, multimodal interaction, and integration, web-everywhere devices, multimedia education, including computer supported collaborative learning and design, and applications of virtual environments.

Q: What is the multimedia research topic that is related to the following projects?

1- Multimedia content analysis 2- Video compression 3- Network protocols 4- Authoring systems 5- Applications of virtual environments Sol.

Multimedia content analysis Multimedia processing and coding Video compression Multimedia processing and coding Network protocols Multimedia system support and networking Authoring systems Multimedia tools, end systems, and applications Applications of virtual environments Multimedia tools, end systems, and applications Q: What are the aims of the following multimedia projects?

1- Camera based object tracking 2- 3D motion capture 3- Digital fashion

Sol. Camera based object tracking: One aim is to develop control systems for industrial control,

gaming, and so on that rely on moving scale models (toys) around a real environment (a board game). Tracking the control objects (toys) provides user control of the process.

3D motion capture: used for multiple actor capture, so that multiple real actors in a virtual studio can be used to automatically produce realistic animated models with natural movement.

Digital fashion: aims to develop smart clothing that can communicate with other such enhanced clothing using wireless communication, so as to artificially enhance human interaction in a social setting.

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Q: Define Multimedia application and give 6 examples on multimedia applications. Multimedia application: is an application which uses a collection of multiple media sources e.g. text, graphics, images, sound/audio, animation and/or video. (6 examples from the following)

1- World Wide Web 2- Multimedia Authoring, e.g. Adobe/Macromedia Director 3- Hypermedia courseware 4- Video-on-demand 5- Interactive TV 6- Computer Games 7- Virtual reality 8- Digital video editing and production systems 9- Multimedia Database systems

Q: What are the main characteristics of the WWW which causes its popularity? The popularity of the WWW is due to:

• The amount of information available from web servers, • The capacity to post such information, • The ease of navigating such information with a web browser.

Q: Define the term W3C and list the three goals of WWW. W3C: World Wide Web Consortium which maintained and developed the WWW technology. The W3C has listed the following three goals for the WWW:

1- Universal access of web resources (by everyone everywhere), 2- Effectiveness of navigating available information, 3- Responsible of posted material.

Q: Define the following terms: WWW, W3C, SGML, HTML, HTTP, XML WWW: World Wide Web W3C: World Wide Web Consortium SGML: Standard Generalized Markup Language HTML: Hypertext Markup Language HTTP: Hypertext Transfer Protocol XML: Extensible Markup Language Q: What are the main processes that multimedia system has to deal with?

1- Generation of data, 2- Manipulation of data, 3- Storage of data, 4- Presentation of data, and 5- Communication of information/data

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Q: List 5 examples on multimedia data.

1- Text or static data 2- Graphics 3- Images 4- Audio 5- Video

Q: Define the hardware devices: ADC and DAC. Do you need ADC for a multimedia data that is already generated by the computer? Why? ADC: Analog-to-Digital converter which is a special hardware device that takes analog signals from analog sensor (e.g. microphone) and digitally sample data. DAC: Digital-to- Analog converter which is a special hardware device that takes digital signal, possible after modification, and outputs an analog signal that may be played by analog output device (e.g. loudspeaker, RGB monitor/display). The data that are generated directly in computer are in binary format and do not require digitizing therefore ADC is not required in this case. Q: Explain how to input the printed text, printed image, and handwritten text to your computer? Printed text can be scanned via optical character recognition Printed image can be scanned via scanner directly to image format Handwritten text can be digitized by electronic pen sensing Q: Define the following terms:

1) Image sampling 2) Image quantization 3) Digital Image

An image may be continuous with respect to the x- and y-coordinates, and also in amplitude • Image sampling is the process of digitizing the coordinate values of the continuous

image. • Image quantization is the process of digitizing the amplitude values of the continuous

image. • When the coordinate values and the amplitude values of the image are all finite, discrete

quantities, we call the image a digital image. Q: Explain the bit-map representation in computing and computer graphics.

• In computing, a bitmap is a mapping from some domain (for example, a range of integers) to bits, that is, values which are zero or one. It is also called a bit array or bitmap index.

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• In computer graphics, when the domain is a rectangle (indexed by two coordinates) a bitmap gives a way to store a binary image, that is, an image in which each pixel is either black or white.

Q: An image of size (640×480) pixels, how many KB are required to store this image in two cases:

1- Binary image

2- Grayscale image

Sol:

1- For binary image each pixel contains 1 bit (either 0 or 1), No. of bits in image = 640*480*1 bit = 307200 bits No. of Bytes = 307200/8=38400 Bytes No. of KB = 38400/1024 = 37.5 KB

2- For grayscale image each pixel contains 8 bits (1 byte) No. of Bytes in image = 307200 Bytes No. of KB = 307200/1024 = 300 KB

Q: Define dithering process and explain the reason behind obtaining a somewhat grainy color.

Dithering is the attempt by a computer program to approximate a color from a mixture of other colors when the required color is not available. The result may appear somewhat grainy since it's composed of different pixel intensities rather than a single intensity over the colored space. Q: Suppose we have available a 600 dot-per-inch (dpi) laser printer, explain how we can print 600 × 600 image using this printer? Such a device can usually only print a dot or not print it. However, a 600 × 600 image will be printed in a 1-inch space and will thus not be very pleasing. Therefore, dithering is used. For printing all a 1-bit printer, dithering is used to calculate larger patterns of dots, such that values from 0 to 255 correspond to pleasing patterns that correctly represent darker and brighter pixel values. The main strategy is to replace a pixel value by a larger pattern, such as 2 × 2 or 4 × 4. Q: Suppose we have a grayscale image and we want to print it, apply the dithering process to convert the following pixel values to larger patterns of dots: 10, 30, 50 Use the following dithering matrix:

8 Dr. Rasha Thabit


Sol: Step 1: re-map pixel values from 0 – 255 to a new range 0 – 16 by dividing the value by (256/17) (and rounding down). Re-map Pixel 1=10 / (256/17) = 0.66 round down 0 Re-map Pixel 2=30 / (256/17) = 1.99 round down 1 Re-map Pixel 3=50 / (256/17) = 3.32 round down 3 Step 2: Replace each pixel by a 4 × 4 dots (binary pixels).

Compare “Re-map Pixel 1” with the given dithering matrix

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0


1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0


1 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0

Q: Write the description for each of the following file formats: GIF, JPEG, TIFF, BMP, and PNG Sol: Format Name Description Recognized

Extensions GIF Graphics Interchange Format .gif JPEG Joint Photographic Experts Group .jpg, .jpeg TIFF Tagged Image File Format .tif, .tiff BMP Windows Bitmap .bmp PNG Portable Network Graphics .png

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Q:

Q:

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Q: What is a color look-up table and how is it used to represent color? Give an advantage and a disadvantage of this representation with respect to true color (24-bit) color. How do you convert from 24-bit color to an 8-bit color look up table representation?

Advantage: Use up significantly less memory than full 24-bit color. Disadvantage: Restricted number of colors available. LUT needs to be built when converting 24-bit color images to 8-bit: grouping similar colors (each group assigned a color entry) Q: GIF and JPEG are two commonly used image representations. Do they usually use lossless or lossy compression? State the major compression algorithm (if lossless) or the lossy steps of the algorithm (if lossy) for each representation.

Q: What is the YIQ color model? How is compression achieved with YIQ in Analog NTSC Video and Digital MPEG Video? NTSC (Analog) Compression Scheme:

• I is red-orange axis, Q is roughly orthogonal to I. • Eye is most sensitive to Y, next to I, next to Q. • Analog Video Compression Scheme:

4 MHz is allocated to Y, 1.5 MHz to I, 0.6 MHz to Q.

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Q:

Sol:

Q: Give three color models other than RGB/CMYK and explain the benefits of using the model by showing a practical application for each model.

Q: Convert the following RGB colors to YUV colors:

1) black RGB color (0,0,0) 2) White RGB color (1,1,1)

Sol:

12 Dr. Rasha Thabit


The conversion matrix is as follows:

1) For black RGB color (0,0,0)

Y=0, U=0, V=0 2) For White RGB color (1,1,1)

Y= 0.299×1 + 0.587×1 + 0.114×1 = 1 U= -0.299×1 - 0.587×1 + 0.886×1 = 0 V= 0.701×1 - 0.587×1 - 0.114×1 = 0

Q: What is the purpose of performing image addition? The result of adding two 8-bit images can range from 0 to 510, what are the methods that can be used to make the result in the acceptable range? Sol:

1) Image addition is used for the averaging of images to reduce noise. 2) To make the result in the acceptable range,

a) One possibility is to divide the result by 2, obtaining a resulting image that is scaled to the 0 to 255 range. A similar approach is applied in image averaging, in which the N images added together produce a total, which is then divided by N to rescale the data.

b) Another possibility is to find the largest and smallest actual values in the sum image and then dynamically rescale the result to this maximum and minimum, so that each pixel is assigned a new value.

Where range is the capacity of the image memory, typically 255.

Q: What is the purpose of performing image subtraction? The result of subtracting two 8-bit images can range from -255 to 255, what are the methods that can be used to make the result in the acceptable range?

1) Image subtraction is used to level images by removing background. There are several applications of subtraction, such as that employed in unsharp masking where the smoothed image is subtracted, pixel by pixel, from the original.

2) To make the result in the acceptable range, a) The data can be rescaled to fit into a single byte, replacing the original image, by dividing

by 2 and adding 128, b) Another possibility is to find the largest and smallest actual values in the subtract image

and then dynamically rescale the result to this maximum and minimum, so that each pixel is assigned a new value.

13 Dr. Rasha Thabit


Where range is the capacity of the image memory, typically 255.

Q: Draw the histogram of the following block from a grayscale image:

Sol:

156 157 159 160 161 162 163 164 165 166 167 170 173 3 2 1 2 3 2 2 5 1 1 1 1 1

Total no. of pixels = 3+2+1+2+3+2+2+5+1+1+1+1+1= 25

Q: What is the indication of the Peaks and Valleys in image histogram? What is the rationale behind performing histogram equalization?

Sol:

• Peaks in the histogram correspond to the more common brightness values, which may correspond to particular structures that are present. Valleys indicate brightness values that are less common in the image.

• The rationale behind histogram equalization is to spread out the displayed brightness levels in the peak areas, compressing them in the valleys so that the same number of pixels in the display show each of the possible brightness levels.

14 Dr. Rasha Thabit

Questions and Answers for Multimedia Computing Part Impu.edu.iq/images/forth_class_comp/multimedia-compressed.pdf · A Multimedia System is a system capable of processing multimedia

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