Standard Codecs: Image Compression to Advanced Video Coding (IET Telecommunications Series)

1. 

In MPEG-1, with the group of picture structure of N = 12 and M = 3, the maximum motion speed is assumed to be 15.5 pixels/frame (half pixel precision), calculate the number of search operations required to estimate the motion in P-pictures with:

1. telescopic method

2. direct on the P-pictures

2. 

In an MPEG-1 encoder, for head-and-shoulders-type pictures, the maximum motion speed for P-pictures is set to 13 pixels and those of the forward and backward for the first B-picture in the subgroup are set to five pixels and nine pixels, respectively.

1. explain why the search range for the B-picture is smaller than that of the P-picture

2. what would be the forward and backward search ranges for the second B-picture in the subgroup?

3. calculate the number of search operations with half pixel precision for the P and B-pictures

3. 

An I-picture is coded at 50 kbits. If the quantiser step size is linearly distributed between 10 and 16, find the complexity index for this picture.

4. 

In coding of SIF-625 video at 1.2 Mbit/s, with a group of pictures (GOP) structure N = 12, M = 3, the ratios of complexity indices of I, P and B are 20: 10: 7, respectively. Calculate the target bit rate for coding of each frame in the next GOP.

5. 

If in problem 4 the allocated bits to B-pictures were reduced by a factor of 1.4, find the new complexity indices and the target bits to each picture type.

6. 

In problem 4 if due to scene change the average quantiser step size in the last P-picture of the GOP was doubled, but those of other pictures did not change significantly:

1. how do the complexity index ratios change?

2. what is the new target bit rate for each picture type?

7. 

If in problem 4 the complexity indices ratios were wrongly set to 1:1:1, but after coding the average quantiser step sizes for I, P and B were 60, 20 and 15 respectively, find:

1. the target bit rate for each picture type before coding

2. the target bit rate for each picture type of the next GOP.

1. 

1. each operation = (2 × l5 + 1)² + 8 = 969, total operations = 3 × 969 = 2907

2. ω = 3 × 15 = 45, total no of operations = (2 x 45 + 1)² + 8 = 8289

2. 

1. the first B-picture is closer to its forward prediction than its backward prediction picture.

2. for the second B-picture, FWD = 9 and BWD = 5

3. for P-picture (2 × 13 + 1)² + 8 = 737, and for each B-picture (2 × 5 + 1)² + 8 + (2 x 9 + 1)² + 8 = 498

3. 

Average and the complexity index is 50 × 1000 × 13 = 65 × 10⁴.

4. 

(8 × 7) + (3 × 10) + 20 = 106

for I-pictures:

for P = 54.3 kbits and for B = 38 kbits.

5. 

The new index ratio for B becomes 7/1.4 = 5

(8 × 5) + (3 × 10) + 20 = 90, and bits for I = 128 kbits, for P = 64 and for B = 32 kbits

6. 

20 + 10 + 10 + 20 + 8 × 7=116

for P, the average index of (10 + 10 + 20)/3 = 13.3 should be used, hence the target bit rates for I = 99.3 kbits, for P = 66.2 kbits and for B = 34.75 kbits.

7. 

1. all equal to 48 kbit/s

2. 60 + 3 × 20+8 × 15 = 240

   For for P = 48 kbits and for B = 36 kbits