ECE-C 490 Image Processing Architectures

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ECE
-
C 490 Image Processing Architectures


Practice Final


Winter 2002
-
3



Do any

(6, VI, 20
3
) problems

All problems have the same weight

Please keep your answers short and to the point.


Problem 1
. A source has three symbols:
a, b, c,
with probabilitie
s
p
(
a
) = 0.95,
p
(
b
) = 0.025,
p
(
c
)
= 0.025

(a) Estimate the average number of bits required to code each of the symbols with an optimal
code.

(b) Assume that we encode a sequence of 100 symbols from this source with an arithmetic
code. Estimate the number o
f code bits required.

Problem 2
. A source produces symbols (integers) over the range
-
128 to 127. All values have
equal probability.

(a) How many bits are needed to code symbols from the source? Use a lossless code.

(b) We are allowed to use a maximum of

3 bits per symbol. Describe a lossy coding method
that achieves this goal.

(c) Estimate the RMS error produced by the method in part (b).

Problem 3.
Assume we have a subroutine that performs
n
-
point DCT transforms. We measure
its speed and find that for
n

= 8 the computation time is 8 microseconds, and for
n

= 16 the time
is 18 microseconds.

(a)

Find the time for computing 8x8 and 16x16 2D DCTs.

(b)

Will 16x16 point DCT processing of an image be faster or slower than 8x8 processing?
By what percentage?

Problem 4
.


(a) In an MPEG
-
1 picture, luminance and chrominance are processed differently. How many
luminance pixels are coded in a SIF? How many chrominance pixels?

(b) What is the main difference between MPEG
-
2 4:2:0 and 4:2:2 profiles? What is the
intended applic
ation of each?

Problem 5
.

(a)

Compare MPEG
-
1 and H.261 standards. What are the intended applications of these
standards? Describe some similarities and differences.

(b)

Is H.263 more similar to MPEG
-
2 or to MPEG
-
4? Explain your answer.

Problem 6
. A video is coded

with an IPBBPBBPBBPBBP picture sequence. The average
compression is 8 for I pictures, 25 for P pictures, and 100 for B pictures.

(a) What is the average compression?

(b) Is the second P picture in the group based on the I picture, the first P picture, or
one of the
B pictures? Explain.

Problem 7
. According to Table 8.1, DCT processing for H.261 (CIF at 30 fps) requires 60
MOPS.

(a) Estimate the computational requirements for DCT processing at QCIF and sub
-
QCIF
picture format. State your assumptions.

(b)
The H.261 CIF picture format is very similar to the MPEG SIF format. Do you expect
that, at the same RMS noise level, the compression for H.261 will be the same as for
MPEG
-
1? Explain.

Problem 8
.

(a) Teleconferencing standards (H.261 and H.263) use only
I and P pictures (no B pictures).
Why?

(b) Which of the two standards is designed to operate at lower bitrates? Name at least one
feature that was used to make this possible.

Problem 9
.

(a) Estimate the storage requirement, in megabytes, for a 120 minute

film with (1) MPEG
-
1,
and (2) MPEG
-
2 at Main level and Main profile.

(c)

According to Table 8.1, motion estimation for H.261 (CIF at 30 fps) requires 608 MOPS.
Assume that the same software subroutines are used for motion estimation in MPEG
-
1.
Estimate the p
rocessing requirements. Explain your calculation.