lecturer notes

1. Video Compression

2. • When colors need to be used in digital
media like cameras and laptops, colors need
to be presented in numbers. because digital
media can only understand numbers. :).
• Therefore color space is a set of rules that
allows describing colors with numbers.
What is a color space?

3. • RGB is a color space. RGB color space uses Red- Green-Blue
component of the color and use those component to display
the color.
• Using these three components, any color can be displayed.
Following figure may give you a better understanding.
What is RGB ? An easy example for a color space.

4.  YCbCr is also same like RGB. Another color space.
• Y is the luma component of the color. Luma component is
the brightness of the color. That means the light intensity of
the color. The human eye is more sensitive to this
component.
 Cb and Cr is the blue component and red component related to
the chroma component. That means “Cb is the blue
component relative to the green component. Cr is the red
component relative to the green component.” These
components are less sensitive to the human eyes.
 Since the Y component is more sensitive to the human eye, it
needs to be more correct and Cb and Cr is less sensitive to the
human eye.
What is YCbCr ?

6. some basic principles of video
compression:
 Earlier H.261 and MPEG 1 and 2 standards. with a
brief introduction of ideas used in new standards
such as H.264 (MPEG-4 Advanced Video Coding).
 Image, video, and audio compression standards have
been specied and released by two main groups since
1985:
 ISO International Standards Organisation: JPEG,
MPEG.
 ITU International Telecommunications
Union:H.261- 264.

7. Compression Standards

8. How to Compress Video?

9. MPEG
• Stands for Moving Picture Experts Group (ISO-
IEC)
• Started in 1988
• Had to come up with a draft of the standard
by 1990
• Received MPEG Proposal from mostly
commercial companies

10. MPEG (cont’d)
• MPEG-Video
• MPEG-Audio
• MPEG-System
– Synchronization of audio and video

11. Requirements
• A Generic Standard
• Random Access
• Fast Forward/Reverse Searches
• Reverse Playback
• Audio Visual Synchronization
• Robustness to Errors

12. Requirements (cont’d)
• Coding/Decoding Delay
• Editability
• Format Flexibility
• Cost Tradeoffs

13. MPEG-VIDEO Compression
• Spacial Redundancy
– Intraframe compression
– DCT compression
• Temporal Redundancy (i.e. motion
compression)
– Interframe compression

14. Discrete Cosine Transform (DCT)
12
0
10
8
90
7
5
6
9
7
3
8
2
89
12
7
11
5
97
8
1
7
5
7
9
8
8
95
13
4
12
2
10
5
8
9
8
3
8
7
9
6
10
3
13
7
12
5
10
7
9
2
8
6
9
0
9
9
10
6
13
1
11
9
10
1
8
6
8
0
8
3
9
3
10
0
11
7
10
5
87
7
2
6
5
6
9
7
8
85
10
0
88 70
5
5
4
9
5
3
6
2
69
89 77 59
4
4
3
8
4
2
5
1
58
0 – black
255 – white

15. DCT (cont’d)
• The 64 (8 x 8) DCT
basis functions
• Superimpose
multiples of these
functions to
simulate the
original picture

16. DCT (cont’d)
0 – black
255 – white
700 90 100 0 0 0 0 0
90 0 0 0 0 0 0 0
-89 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0

17. DCT (cont’d)
700 90 90 -89 0 100 0 0 0 .... 0
700 90 100 0 0 0 0 0
90 0 0 0 0 0 0 0
-89 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0

18. Motion Compensation
• I-Frame
– Independently
reconstructed
• P-Frame
– Forward predicted
from the last I-
Frame or P-Frame
• B-Frame
– forward predicted
and backward
predicted from the
last/next I-frame or
P-frame
Transmitted as - I P B B B P B B B

19. Motion Prediction

20. Motion Estimation

21. Motion Estimation (cont’d)

22. https://www.mathworks.com/help/images/ref
/rgb2ycbcr.html