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Slide 1
Image Formation and Digital Video Making Pictures
Slide 2
Slide 3
Objectives Review how a digital image is created What is
digital? Compression
Slide 4
0101010000111100011110001 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
Slide 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 = 1 Frame
Slide 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
Slide 7
Fields and Frames 2 fields (1 odd & 1 even) = 1 frame 30
frames = 1 second of video
Slide 8
Scan types - Progressive Progressive scan Display all lines on
each frame New fixed-resolution displays (such as LCD, LED) all use
progressive scan
Slide 9
Lets Do the Math! 1 minute, 34 seconds
Slide 10
Definitions Bit rate Information stored/transmitted per unit
time Usually measured in Mbps (Megabits per second) Ranges from 40
Mbps Resolution Number of pixels per frame Ranges from 160x120 to
1920x1080 FPS (frames per second) Usually 24, 25, 30, or 60
Slide 11
Definitions Resolution Number of pixels per frame Ranges from
160x120 to 1920x1080 The more lines of resolution, the better the
image
Slide 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
Slide 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
Slide 14
Which Would You Buy? 50 inch, 720p $399 32 inch, 1080i $499 29
inch, 1080p $299
Slide 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
Slide 16
Sampling Samples are taken of an analog signal at equal
intervals Larger samples in shorter time frames = higher sample
rate Larger samples in shorter time frames = lower sample rate High
Rate Low Rate
Slide 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.
Slide 18
Digital Compression LOSSY vs. LOSSLESS
Slide 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
Slide 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
Slide 21
Loss of Resolution Original (63 kb) Low (7kb) Very Low (4
kb)
Slide 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
Slide 23
Close-up details of different JPEG compression ratios
Uncompressed image (roughness between pixels still visible) Half
compression, blurring & halos around sharp edges Max
compression, 8-pixel blocks apparent, large distortion in
high-frequency areas
Slide 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
Slide 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?