Exam 7: Multimedia Network Communications and Applications, Wireless Networks and Content-Based Retrieval in Digital Libraries

What is the meaning of the "horseshoe" shape in the chromaticity diagram? (b) Where does that curve come from? - i.e., how is it calculated?

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Question 1

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a) Human vision can see colors only within that boundary.
b) We have measured the $\bar{x}(\lambda), \bar{y}(\lambda), \bar{z}(\lambda)$ curves from human color-matching experiments. The boundary, in 3D XYZ color space, of these curves is the boundary of all the colors that a person can see. If we make chromaticity out of the curves themselves, $\{x, y\}=\{\bar{x}(\lambda), \bar{y}(\lambda)\} /(\bar{x}(\lambda)+\bar{y}(\lambda)+\bar{z}(\lambda))$ then we end up with the horseshoe shape.

Explain the following terms: (a) Image Resolution (b) Bitmap

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(a) Size in pixels, usually width $\mathrm{x}$ height
(b) A representation consisting of rows and columns of pixels of an image in computer memory. The value of each storage location is one or more bits. The more bits used to represent a pixel, the more colors or shades of gray that can be represented.

$etc. Notes: ' x ' in status byte hex value stands for a channel number. (a) 1) Is the Pitch Bend MIDI message a Channel Message? 2) The Pitch Bend opcode in MIDI is followed by two data bytes specifying how the control is to be altered. How many bits of accuracy does this amount of data correspond to? Why? 3) The MIDI communications standard specifies 31250 bps (bits per sec); how many Pitch Bend messages could be sent in 3 seconds if the message stream consisted only of Pitch Bend messages? (b) The note A above Middle C (with frequency 440 \mathrm{~Hz} is note 69 in General MIDI. What MIDI bytes (in hex) should be sent to play a note twice the frequency of (i.e., one octave above) A above Middle C at maximum volume on channel 1? (Don't include start/stop bits.) Information: An octave is 12 steps on a piano, i.e., 12 notes up.$ etc. Notes: ' $x$ ' in status byte hex value stands for a channel number. (a) 1) Is the Pitch Bend MIDI message a Channel Message? 2) The Pitch Bend opcode in MIDI is followed by two data bytes specifying how the control is to be altered. How many bits of accuracy does this amount of data correspond to? Why? 3) The MIDI communications standard specifies 31250 bps (bits per sec); how many Pitch Bend messages could be sent in 3 seconds if the message stream consisted only of Pitch Bend messages? (b) The note "A above Middle C" (with frequency $440 \mathrm{~Hz}$ is note 69 in General MIDI. What MIDI bytes (in hex) should be sent to play a note twice the frequency of (i.e., one octave above) "A above Middle C" at maximum volume on channel 1? (Don't include start/stop bits.) Information: An octave is 12 steps on a piano, i.e., 12 notes up.

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Question 3

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a) 1) Yes, since must specify which instrument to bend.
2) 14, since each data byte starts with a leading 0 (and the 0 start and stop bits in 10-bit MIDI bytes should not be counted).
3) 3 sec $=3 * 31250$ bits, each byte of length 10 (incl. 1 start and 1 stop bit), 3 bytes per message $3^{*} 31250 / 10 / 3=3125$ messages.
b) $a) 1) Yes, since must specify which instrument to bend. 2) 14, since each data byte starts with a leading 0 (and the 0 start and stop bits in 10-bit MIDI bytes should not be counted). 3) 3 sec =3 * 31250 bits, each byte of length 10 (incl. 1 start and 1 stop bit), 3 bytes per message 3^{*} 31250 / 10 / 3=3125 messages. b)$

What is Signal to Quantization Noise Ratio (SQNR)? (b) How does an additional 2 bits affect the SQNR? (c) Explain why the worst SQNR occurs when the sample equals half of the interval.

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Question 4

Thinking about my large collection of . jpg images, I decide to unify them and make them more accessible by simply combining them into a big . mpg file by simply treating them as frames in a video: my reasoning is that I can simply use a viewer to step through the file, thus making a cohesive whole out of my collection. Comment on the utility of this idea, in terms of the compression ratio achievable for the set of images.

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Question 5

Suppose we have a small 8-bit grayscale image, with all pixels equal to the same pixel value, say 113. Consider the performance of an LZW compression scheme. First initialize codes in the dictionary with pixel values, $0 . .255$ . Use 9-bit codes. For a $4 \times 4$ uniform image made of pixel values which are all 113, how many bits will LZW (i.e., PKZIP, WINZIP, etc.) use for a compressed version of the image? Explain in detail, using an LZW table. What is the compression ratio? Hint: recall that the LZW coding algorithm is $Suppose we have a small 8-bit grayscale image, with all pixels equal to the same pixel value, say 113. Consider the performance of an LZW compression scheme. First initialize codes in the dictionary with pixel values, 0 . .255 . Use 9-bit codes. For a 4 \times 4 uniform image made of pixel values which are all 113, how many bits will LZW (i.e., PKZIP, WINZIP, etc.) use for a compressed version of the image? Explain in detail, using an LZW table. What is the compression ratio? Hint: recall that the LZW coding algorithm is Answer:$ Answer:

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Question 6

An original $8 \times 8$ color "checkerboard" $\mathrm{CMY}$ image is shown below in which the two colors are $\mathrm{C} 1:(\mathrm{C}=255, \mathrm{M}=155$ , $\mathrm{Y}=255)$ and $\mathrm{C} 2:(\mathrm{C}=\mathrm{M}=\mathrm{Y}=100)$ , where $[0 . .255]$ is the range for the three color components. You are asked to convert the color CMY image to YIQ images using 4:1:1 chroma subsampling. (In subsampling, you should use an averaging method so you are not selectively throwing away information from certain pixels.) $An original 8 \times 8 color checkerboard \mathrm{CMY} image is shown below in which the two colors are \mathrm{C} 1:(\mathrm{C}=255, \mathrm{M}=155 , \mathrm{Y}=255) and \mathrm{C} 2:(\mathrm{C}=\mathrm{M}=\mathrm{Y}=100) , where [0 . .255] is the range for the three color components. You are asked to convert the color CMY image to YIQ images using 4:1:1 chroma subsampling. (In subsampling, you should use an averaging method so you are not selectively throwing away information from certain pixels.) (a) Show all pixel values of each of the YIQ images generated from the given CMY color image. (b) Besides their low resolution, do the chrominance images maintain enough information in this case? What does this tell? Note: The relationship between RGB and YIQ is approximately: \left[\begin{array}{l} Y \\ I \\ Q \end{array}\right]=\left[\begin{array}{rrr} 0.3 & 0.6 & 0.1 \\ 0.6 & -0.3 & -0.3 \\ 0.2 & -0.5 & 0.3 \end{array}\right]\left[\begin{array}{l} R \\ G \\ B \end{array}\right]$ (a) Show all pixel values of each of the YIQ images generated from the given CMY color image. (b) Besides their low resolution, do the chrominance images maintain enough information in this case? What does this tell? Note: The relationship between RGB and YIQ is approximately: $\left[\begin{array}{l}Y \\I \\Q\end{array}\right]=\left[\begin{array}{rrr}0.3 & 0.6 & 0.1 \\0.6 & -0.3 & -0.3 \\0.2 & -0.5 & 0.3\end{array}\right]\left[\begin{array}{l}R \\G \\B\end{array}\right]$

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Question 7

We have spent time looking at the question of how to minimize the entropy. Suppose now we find a mechanism for maximizing the entropy instead. In terms of a grayscale image, this mechanism would re-map the pixel values to new ones. Roughly, what would be the result of such a re-mapping; i.e., what would the resulting image look like? Answer:

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Question 8

Suppose an alphabet consists of 6 symbols, and the probability for each of the symbols is $1 / 6$ . (Note, $\log _{2}(3)=1.585$ ) (a) What is the entropy for this set? (b) Draw the Shannon-Fano tree for this set. What is the average bitrate? (c) Draw the Huffman tree for this set. What is the average bitrate? (d) How many bits would we need without compression, assuming fixed-length codewords? What is the compression ratio, compared to the Huffman tree?

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Question 9

The "hue" is the colour, independent of brightness and how much pure white has been added to it. We can make a simple definition of hue as the set of ratios R:G:B. Suppose a colour (i.e., an RGB) is divided by 2.0, so that the RGB triple now has values 0.5 times its former values. Explain using numerical values: (a) If gamma-correction is applied after the division by 2.0 and before the colour is stored, does the darker RGB have the same hue as the original in the sense of having the same ratios R:G:B of light emanating from the CRT display device? (we're not discussing any psychophysical effects that change our perception - here we're just worried about the machine itself). (b) If gamma-correction is not applied, does the second RGB have the same hue as the first RGB, when displayed? (c) For what colour triples is the hue always unchanged?

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Question 10

It is known that a loss of audio output at both ends of the audible frequency range is inevitable due to the frequency response function of audio amplifier and medium (e.g., tape). (a) If the output was 1 volt for frequencies at mid-range, after a loss of $\quad-3 \mathrm{~dB}$ at $18 \mathrm{kHz}$ what is the output voltage at this frequency? [Hint: Assume $\log _{10} 2=0.3$ .] (b) To compensate the loss, a listener can adjust the gain (and hence the output) at different frequencies from an equalizer. If the loss remains $-3 \mathrm{~dB}$ and a gain through the equalizer is $6 \mathrm{~dB}$ at $18 \mathrm{kHz}$ , what is the output voltage now?

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Question 11

In Adaptive Huffman coding using a special NYT code and a 5-bit set of initial codes for an input source consisting of 26 characters, which takes more CPU time, encoding or decoding? Briefly explain.

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Question 12

Given the Lempel-Ziv-Welch (LZW) Decompression Algorithm, read a character $k$ ; output $k$ ; show how the algorithm will decode the following (using the table like that below). THERE_A<259>_<256><259><260><256>INGS! ! Note: Assume that new multi-character entries start at index 256.

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Question 13

When we view video on a computer, the analog video is digitized and stored in the frame buffer of the video "frame grabber" card. Suppose that a video is digitized at (integer) NTSC frame rate, has size $640 \times 480$ pixels, and is stored with a bit depth of 24 bits. We're interested in displaying the captured video. (a) What must be the minimal bandwidth of the system bus in Mbps when data is moved from the video frame grabber to the memory for video display? (b) How much storage capacity (in GBytes) is required to store 1 minute of this video? (c) Explain why you don't see a flicker effect on your workstation screen when displaying this video at NTSC frame rate?

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Question 14

Suppose you have a dedicated channel with fixed bandwidth, and you would like to provide channel surfing capabilities which restrict you from using more than one second delay in video decoding.

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Question 15

The note "A above Middle C" (with frequency $440 \mathrm{~Hz}$ ) is note 69 in General MIDI. What MIDI bytes (in hex) should be sent to play a note twice the frequency of (i.e., one octave above) "A above Middle C" at maximum volume on "Channel 1"? (Don't include start/stop bits.) Information: An octave is 12 steps on a piano, i.e., 12 notes up. $The note A above Middle C (with frequency 440 \mathrm{~Hz} ) is note 69 in General MIDI. What MIDI bytes (in hex) should be sent to play a note twice the frequency of (i.e., one octave above) A above Middle C at maximum volume on Channel 1? (Don't include start/stop bits.) Information: An octave is 12 steps on a piano, i.e., 12 notes up. (b) What bytes should be sent immediately after that?$ (b) What bytes should be sent immediately after that?

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Question 16

Suppose that in MPEG our program detects errors in transmission (over wireless, say), and we know that, for some macroblock, we have correctly received the motion vector, but the DCT coefficient information is damaged. What should we do to promote error concealment? Answer:

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Question 17

List three QoS parameters for multimedia transmission and explain for some specific applications how the values of these parameters are affected by the application data.

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Question 18

In the simplest version of the median-cut algorithm, does it make any difference whether we assign bits in the order RGBRGBRG, or GBRGBRGB, etc. Explain. (b) Suppose we decide to quantize an 8-bit grayscale image down to just 2 bits of accuracy. What is the simplest way to do so? What ranges of byte values in the original image are mapped to what quantized values?

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Question 19

What is the advantage of interlaced video? What are some of its problems? (b) NTSC video has 525 lines per frame and $63.5 \mu$ sec per line, with 20 lines per field of vertical retrace and $10 \mu$ sec horizontal retrace. 1) Where does the $63.5 \mu \mathrm{sec}$ come from? 2) Which takes more time, horizontal retrace or vertical retrace? How much more time?

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Question 20

Showing 1 - 20 of 52

What is the meaning of the "horseshoe" shape in the chromaticity diagram? (b) Where does that curve come from? - i.e., how is it calculated?

Explain the following terms: (a) Image Resolution (b) Bitmap

What is Signal to Quantization Noise Ratio (SQNR)? (b) How does an additional 2 bits affect the SQNR? (c) Explain why the worst SQNR occurs when the sample equals half of the interval.

In Adaptive Huffman coding using a special NYT code and a 5-bit set of initial codes for an input source consisting of 26 characters, which takes more CPU time, encoding or decoding? Briefly explain.

Given the Lempel-Ziv-Welch (LZW) Decompression Algorithm, read a character $k$ ; output $k$ ; show how the algorithm will decode the following (using the table like that below). THERE_A<259>_<256><259><260><256>INGS! ! Note: Assume that new multi-character entries start at index 256.

Suppose you have a dedicated channel with fixed bandwidth, and you would like to provide channel surfing capabilities which restrict you from using more than one second delay in video decoding.

Suppose that in MPEG our program detects errors in transmission (over wireless, say), and we know that, for some macroblock, we have correctly received the motion vector, but the DCT coefficient information is damaged. What should we do to promote error concealment? Answer:

List three QoS parameters for multimedia transmission and explain for some specific applications how the values of these parameters are affected by the application data.

Multimedia Authoring, Tools, Graphics and Image Data Representations

Color in Image and Video

Fundamental Concepts in Video and Basics of Digital Audio

Lossless Compression Algorithms

Lossy Compression Algorithms, Image Compression Standards and Basic Video Compression Techniques

Mpeg Video Coding I -- Mpeg-1 and 2, Basic Audio Compression Techniques, Mpeg Audio Compression, Computer and Multimedia Networks

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Exam 7: Multimedia Network Communications and Applications, Wireless Networks and Content-Based Retrieval in Digital Libraries

What is the meaning of the "horseshoe" shape in the chromaticity diagram? (b) Where does that curve come from? - i.e., how is it calculated?

Explain the following terms: (a) Image Resolution (b) Bitmap

What is Signal to Quantization Noise Ratio (SQNR)? (b) How does an additional 2 bits affect the SQNR? (c) Explain why the worst SQNR occurs when the sample equals half of the interval.

In Adaptive Huffman coding using a special NYT code and a 5-bit set of initial codes for an input source consisting of 26 characters, which takes more CPU time, encoding or decoding? Briefly explain.

Given the Lempel-Ziv-Welch (LZW) Decompression Algorithm, read a character kkk ; output kkk ; show how the algorithm will decode the following (using the table like that below). THERE_A<259>_<256><259><260><256>INGS! ! Note: Assume that new multi-character entries start at index 256.

Suppose you have a dedicated channel with fixed bandwidth, and you would like to provide channel surfing capabilities which restrict you from using more than one second delay in video decoding.

Suppose that in MPEG our program detects errors in transmission (over wireless, say), and we know that, for some macroblock, we have correctly received the motion vector, but the DCT coefficient information is damaged. What should we do to promote error concealment? Answer:

List three QoS parameters for multimedia transmission and explain for some specific applications how the values of these parameters are affected by the application data.

Multimedia Authoring, Tools, Graphics and Image Data Representations

Color in Image and Video

Fundamental Concepts in Video and Basics of Digital Audio

Lossless Compression Algorithms

Lossy Compression Algorithms, Image Compression Standards and Basic Video Compression Techniques

Mpeg Video Coding I -- Mpeg-1 and 2, Basic Audio Compression Techniques, Mpeg Audio Compression, Computer and Multimedia Networks

Filters

Given the Lempel-Ziv-Welch (LZW) Decompression Algorithm, read a character $k$ ; output $k$ ; show how the algorithm will decode the following (using the table like that below). THERE_A<259>_<256><259><260><256>INGS! ! Note: Assume that new multi-character entries start at index 256.