1. Image Formation and Digital Video
Making Pictures
Image Formation and Digital Video

3. Objectives Review how a digital image is created What is digital?
Compression

4.
What is digital?
Digital uses on/off values to create an image.
The on state is represented by a 1
The off state is represented by a 0
This is known as binary code
The Digital Process

5. Scanning
The 3 beams “read” the screen; from left to right and top to bottom
There are two types of scanning Interlaced & Progressive
Example of Interlace Scanning
Odd lines Even lines Final image
Odd Lines Even Lines = Frame

6. Scan types Interlaced scan
Odd and even lines displayed on alternate frames
When displaying interlaced video on a progressive scan display, can see “comb effect”

7. 2 fields (1 odd & 1 even) = 1 frame 30 frames = 1 second of video
Fields and Frames
2 fields (1 odd & 1 even) = 1 frame 30 frames = 1 second of video

8. Scan types - Progressive
Progressive scan
Display all lines on each frame
New “fixed-resolution” displays (such as LCD, LED) all use progressive scan

9. Let’s Do the Math!
1 minute, 34 seconds

10. Definitions Bit rate Information stored/transmitted per unit time
Usually measured in Mbps (Megabits per second)
Ranges from < 1 Mbps to > 40 Mbps
Resolution
Number of pixels per frame
Ranges from 160x120 to 1920x1080
FPS (frames per second)
Usually 24, 25, 30, or 60

11. Definitions Resolution Number of pixels per frame
Ranges from 160x120 to 1920x1080
The more lines of resolution, the better the image

12. HDTV vs. SDTV What is HDTV – High Definition Television
- Best broadcast quality image
- Superior color and resolution
-16x9 aspect ratio
What is SDTV – Standard Definition Television
- Older TV standard
- Only 525 lines of resolution
- 4x3 aspect ratio

13. Numbers
1920 x 1080
720 x 480
1280 x 720
1440 x 1080
4K TVs: 4000 lines of resolution
Pixels X number of lines of resolution

14. Which Would You Buy? 29 inch, 1080p $299 32 inch, 1080i $499

15. Analog vs. Digital
Analog is an electronic copy of the original. It is continuous and never skips any part of the signal.
Digital is discontinuous. It takes the signal and selects points at equal intervals to represent the original…..this is called sampling

16. Sampling Samples are taken of an analog signal at equal intervals
Larger samples in shorter time frames = lower sample rate
Larger samples in shorter time frames = higher
sample rate
Low Rate
High Rate

17. Compression
Once video is in digital format, it makes sense to compress it
Store video data as efficiently as possible
Maximize quality and minimize storage space and processing resources
CODECS are used to compress and decompress files.

18. Digital Compression
LOSSY vs. LOSSLESS

19. Digital Compression
2 Kinds of Compression: Lossless & Lossy Lossless: Rearranges information rather than getting rid of it Advantage – maintains original file Disadvantage – Makes large files, too large to transfer, stream or download

20. Compression
Lossy: Gets rid of unnecessary information Advantage – Makes file considerably smaller for use on a computer, uploading, streaming etc. Disadvantage – Reduces picture and sound quality What compression you use, depends on the final output of the project: DVD – Lossless Tape - Lossless iPod- Lossy Web- Lossy

21. Loss of Resolution
Original (63 kb)
Low (7kb)
Very Low (4 kb)

22. Downloading vs. Streaming media
Data must completely download before you can play the whole thing
Can watch at the information is being sent to your computer- like watching TV

23. Close-up details of different JPEG compression ratios
Half compression, blurring & halos around sharp edges
Max compression, 8-pixel blocks apparent, large distortion in high-frequency areas
Uncompressed image (roughness between pixels still visible)

24. Streaming media Common types include Flash, RealVideo, Quicktime
Video is played back in “real time”.
Video and audio are compressed to fit inside bandwith

25. Review
What is the difference between interlaced and progressive scanning?
Why do we compress files?
What are the two types of compression we use?
How many frames are there is 1 second of video?