Question 1

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.

Accepted Answer

The answer of In Adaptive Huffman coding using a special...

Question 2

Another name for zig-zag coding is "zonal coding". Suppose you invent a new zonal coding scheme for JPEG that simply discards anti-diagonals above the first few - i.e., we discard the higher frequency ones. Suppose we keep the first six zig-zag lines.
(a) How many coefficients are we keeping?
(b) How will we do, compared to keeping all the zig-zags (still using run-length encoding). Comment on both compression capability and image quality.

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The answer of Another name for zig-zag coding is "zonal...

Question 3

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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The answer of Suppose that in MPEG our program detects...

Question 4

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?

Accepted Answer

The answer of What is the advantage of interlaced video?...

Question 5

In many Computer Graphics applications, $\gamma$-correction is performed only in a color LUT (look-up table).
Give pseudocode for how to make such a lookup table, for an 8-bit CLUT, if it is meant for use in $\gamma$-correction.
Show the first 5 entries of the color LUT.

Accepted Answer

The answer of In many Computer Graphics applications, $\gamma$-correction is...

Question 6

Assume an analog halftoning process uses a screen size of 200 "dots" (disks) per inch, with any size available. Suppose we wish to approximate this digitally, with about 100 intensity levels, not by using an ordered dither but by using an $n \times n$ pattern for each pixel.
How many bilevel dots per inch must our printer be capable of producing?

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The answer of Assume an analog halftoning process uses a...

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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The answer of We have spent time looking at the...

Question 8

Suppose a square image has $N^{2}$ pixels. We would like to approximately know how many pixels there are in total in a $(P+1)$-level image pyramid consisting of the original image plus $P$ smaller images, each of which is $1 / 4$ the size. As a first approximation, let's just count all possible levels, down to a size 1x1 image.
(a) First, suppose $N$ is a power of 2 .
What is an expression for the exact count of pixels in this case, if $N=2^{M}$ ?
What is the exact count of pixels in this case, if $N=16$ ? Write the total as a binary and as a decimal number.
(b) Suppose $N$ is not a power of 2 .
Just give an upper bound for the number of pixels, assuming there are an infinite number of pyramid levels and we can use floats for numbers of pixels. What is this upper bound if $N=16$ ?
Hint: for $x<1$ the Taylor series expansion of $1 /(1-x)$ is $1+x+x^{2}+x^{3}+\ldots$. What does this mean if $x=1 / 4$ ?

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The answer of Suppose a square image has $N^{2}$ pixels....

Question 9

State Shannon-Fano Algorithm.
(b) Complete the following table using the Shannon-Fano Algorithm
  (c) What is the entropy of this source, and in what units? Compare to the above result.

Accepted Answer

The answer of State Shannon-Fano Algorithm.
(b) Complete the following table...

Question 10

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.

Accepted Answer

The answer of Given the Lempel-Ziv-Welch (LZW) Decompression Algorithm,
read a...

Question 11

In JPEG, each nonzero AC coefficient is described by a composite 8-bit value I='nnnnssss', where 'nnnn' codes the runlength and 'ssss' codes the category. Every DCT coefficient has a category $k$, where values are in the range $\left[2^{k-1}, 2^{k}-1\right]$ or $\left[-2^{k}+1,-2^{k-1}\right]$, with $1 \leq k \leq 10$ for the baseline system. For category $k$, it is necessary to send $k$ bits to specify the sign and the magnitude of the actual DCT coefficient itself.
The 4 bits 'nnnn' give the position of the current coefficient relative to the previous nonzero coefficient, i.e., the runlength of zero coefficients from the previous nonzero coefficient. The runlengths specified by 'nnnn' may range from 0 to 15 , and a separate symbol, $I=' 11110000$ ' $=240$ represents a runlength of 16 zero coefficients. If the runlength $>16$ zero coefficients, it is coded by using multiple symbols. A special symbol, $\mathrm{I}=0$, is used to code the end of block (EOB), signaling all remaining coefficients in the block are zero.
The composite symbols for each block are then Huffman coded, followed by additional bits for the sign and magnitude of the actual DCT coefficient itself.
Question: How many elements are there in the total symbol set for Huffman coding, encompassing categories, runlengths, and additional symbols? (we're not concerned with the sign and magnitude bits, here.)

Accepted Answer

The answer of In JPEG, each nonzero AC coefficient is...

Question 12

In MPEG, what are all the different kinds of frames?
(b) What are they used for?
(c) Is the method that is used for motion compensation in MPEG based on x, y translation the most complicated method for motion compensation in use now in any standard? If so, explain why; if not, explain what other method is used.
(d) Does MPEG video compression require a higher bitrate for video clips that have more action in them? Explain.

Accepted Answer

The answer of In MPEG, what are all the different...

Question 13

Compare and contrast the
(a) bandwidth (i.e., bitrate), and
(b) playback requirements of uncompressed digital audio and video.

Accepted Answer

The answer of Compare and contrast the
(a) bandwidth (i.e., bitrate),...

Question 14

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.

Accepted Answer

The answer of What is Signal to Quantization Noise Ratio...

Question 15

Dissolve: Suppose we have video1 dissolving into video2, over a time $t$ from 0 to $t_{\max }$ (video1 gradually disappears, and video2 gradually appears).
There are 2 ways that this task is commonly carried out: "Ordinary Dissolve" and "Dither Dissolve". In Ordinary Dissolve, every pixel value is changed, over time, so that it contains partly the contents of video1 and partly the contents of video2, summed additively. In Dither Dissolve, pixels are either all-video1 or all-video2, not a mix; the decision of which video to take pixel values from is based on a random number generator.
Write pseudocode solutions for accomplishing these two kinds of gradual video transition. For each type, just show the algorithm for filling up R (Red) values - Green and Blue will be similar.

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The answer of Dissolve: Suppose we have video1 dissolving into...

Question 16

In MIDI, for Channel Messages, how many different "opcodes" can there be in the Status Byte? Why?

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The answer of In MIDI, for Channel Messages, how many...

Question 17

In many Computer Graphics applications, $\gamma$- correction is performed only in a color LUT (look-up table). Show the first 5 entries of the color LUT if it is meant for use in $\gamma$-correction.

Accepted Answer

The answer of In many Computer Graphics applications, $\gamma$- correction...

Question 18

To makes matters simpler for eventual printing, we buy a camera equipped with CMY sensors, as opposed to RGB sensors (CMY cameras are in fact available).
(a) Draw spectral curves roughly depicting what such a camera's sensitivity to wavelength might look like.
(b) Could the output of a CMY camera be used to produce ordinary RGB pictures? How?

Accepted Answer

The answer of To makes matters simpler for eventual printing,...

Question 19

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?

Accepted Answer

The answer of What is the meaning of the "horseshoe"...

Question 20

Suppose you wish to transmit a stereo audio signal through a 1 mega-bit/s connection in real time. Consider the following scenarios:
i) You are using a sampling frequency of $44.1 \mathrm{kHz}$. What is the maximum average number of bits can you use to represent an audio sample?
ii) You want to use $16 \mathrm{bit} / \mathrm{sample} / \mathrm{channel}$ representation. What is the maximum sampling frequency? What will you need to do in order to avoid aliasing?
iii) You want to use a sampling frequency of $44.1 \mathrm{KHz}$, and also want use $16 \mathrm{bit} / \mathrm{sample} / \mathrm{channel}$ representation. What is the minimum compression ratio you need in order to transmit the audio signal?

Accepted Answer

The answer of Suppose you wish to transmit a stereo...

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

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.

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:

In many Computer Graphics applications, $\gamma$ -correction is performed only in a color LUT (look-up table). Give pseudocode for how to make such a lookup table, for an 8-bit CLUT, if it is meant for use in $\gamma$ -correction. Show the first 5 entries of the color LUT.

State Shannon-Fano Algorithm. (b) Complete the following table using the Shannon-Fano Algorithm (c) What is the entropy of this source, and in what units? Compare to the above result.

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.

Compare and contrast the (a) bandwidth (i.e., bitrate), and (b) playback requirements of uncompressed digital audio and video.

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 MIDI, for Channel Messages, how many different "opcodes" can there be in the Status Byte? Why?

In many Computer Graphics applications, $\gamma$ - correction is performed only in a color LUT (look-up table). Show the first 5 entries of the color LUT if it is meant for use in $\gamma$ -correction.

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?

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

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.

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:

In many Computer Graphics applications, γ\gammaγ -correction is performed only in a color LUT (look-up table). Give pseudocode for how to make such a lookup table, for an 8-bit CLUT, if it is meant for use in γ\gammaγ -correction. Show the first 5 entries of the color LUT.

State Shannon-Fano Algorithm. (b) Complete the following table using the Shannon-Fano Algorithm (c) What is the entropy of this source, and in what units? Compare to the above result.

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.

Compare and contrast the (a) bandwidth (i.e., bitrate), and (b) playback requirements of uncompressed digital audio and video.

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 MIDI, for Channel Messages, how many different "opcodes" can there be in the Status Byte? Why?

In many Computer Graphics applications, γ\gammaγ - correction is performed only in a color LUT (look-up table). Show the first 5 entries of the color LUT if it is meant for use in γ\gammaγ -correction.

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?

In many Computer Graphics applications, $\gamma$ -correction is performed only in a color LUT (look-up table). Give pseudocode for how to make such a lookup table, for an 8-bit CLUT, if it is meant for use in $\gamma$ -correction. Show the first 5 entries of the color LUT.

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.

In many Computer Graphics applications, $\gamma$ - correction is performed only in a color LUT (look-up table). Show the first 5 entries of the color LUT if it is meant for use in $\gamma$ -correction.