Transcript Document

Video Processing
Lecturer
Dr. Aree Ali Mohammed
2012-2013
4th Stage
[email protected]
18-Jul-15
School of Science \ Computer
Science Dept.
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Overview
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Video Frames
Frame Rates
Analogue Video
Type of Analogue Video Signal File Size and Formats
Progressive and Interlaced Scan
Video File Size Calculation
Video Quality Estimation
Video Processing
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Video Frames
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Video streams are made up of a series of still images (frames)
played one after another at high speed
This fools the eye into believing that it is observing a continuous
stream
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Video (real-world pictures)
Animation (Computer generated)
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Frame Rate
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This is the number of frames per second that are
displayed
PAL (Phase Alternating Line) in Hong Kong produces
25fps.
When producing video for the web we can save data
by using lower frame rates
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e.g. 20fps, 15fps etc
Below 15fps playback becomes noticeably jerky
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Analogue video
• Composite analogue video has all the
components:
brightness,
colour
synchronization.Then,
combined
into
signal for delivery
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video
and
one
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Analogue video
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Component video sends the signals separately
(e.g. S-video, RGB)
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Advantages: Good video quality.
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Disadvantages:
(i) Higher bandwidth compared with
Composite video.
(ii) Synchronization problem between
different colour components.
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Representations
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Composite
 NTSC - 6MHz (4.2MHz video), 29.97 frames/second
 PAL - 6-8MHz (4.2-6MHz video), 50 frames/second
Component
 Separation video (luma, chroma) - svhs, Hi8mm
 RGB, YUV, YIQ,, …
 YCRCB - used for most compressed representations
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S-Video
 As a compromise, (Separated video, or Super-video)
uses two wires, one for luminance and another for a
composite chrominance signal.
 As a result, there is less crosstalk between the color
information and the crucial gray-scale information.
The reason for placing luminance into its own part of
the signal is that black-and-white information is most
crucial for visual perception.
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Analog Video Representations
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NTSC
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Y = 0.299R + 0.587G + 0.114B
I = 0.596R - 0.275G - 0.321B
Q = 0.212R - 0.523G + 0.311B
composite = Y + Icos(Fsc t) + Qsin(Fsc t)
PAL
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Y = 0.299R + 0.587G + 0.114B
U = 0.492(B-Y)
Q = 0.877(R-Y)
composite = Y + Usin(Fsc t) + Vcos(Fsc t)
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Type of TV Video Signal
• There are four analog video formats
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PAL
NTSC
SECAM
HDTV (may be mixed analogue/digital)
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Type of Analogue Video Signal
PAL (Phase Alternate Line)
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Standard television format used in Hong Kong,
China, Europe, UK, Australia and South Africa
Consists of 625 scan lines drawn every 1/25
second with a 4:3 aspect ratio *
PAL is interlaced at 50 cycles per second
PAL uses the YUV color model
* Aspect ratio is the comparison of width to
height for a viewing area. Two common ratios 4:3 and 16:9.
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Type of Analogue Video Signal
NTSC (National Television Standards Committee)
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The American and Japanese standard
Consists of 525 scan lines drawn every 1/30
second
(To be precise, the frame rate of NTSC is 29.97)
Has a 4:3 aspect ratio
NSTC uses the YIQ colour model
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Type of Analogue Video Signal
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SECAM ( Sequential Color with Memory )
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Format in France.
Used 625 scan lines and is interlaced at 50
cycles per second.
HDTV ( High Definition Television)
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based on 720 scan lines or higher, progressive
scan with 16:9 aspect ratio
many standards
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Type of Analogue Video Signal
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Progressive Scan
 Used in normal computer monitor.
 As shown in Figure 1(a), the electronic or optic beam of an
analog video camera continuously scans the imaged
region from the top to bottom and then back to the top.
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Interlaced Scan
 A refresh rate of at least 50 Hz or 50 fps is required in
order for us to perceive the smooth movement of a
video.
 However, it is not feasible to display 50 fps in our
analog TV. Thus, interlaced scan was introduced to
solve this problem.
 In interlaced scan, each frame is scanned in two
fields and each field contains half the number of lines
in a frame.
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Interlaced Scan
 Field containing the first line and following
alternating lines in a frame is called top field. Field
containing the second line and following
alternating lines is called bottom field.
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Interlaced scan produces two fields for each frame.
(a) The video frame, (b) Field 1, (c) Field 2, (d) Difference of fields
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Interlaced Scan
Odd field
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Even field
Interlace scan
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Aspect Ratio/Refresh Rate
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Aspect ratio
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Conventional TV is 4:3 (1.33)
HDTV is 16:9 (2.11)
Cinema uses 1.85:1 or 2.35:1
Refresh Rate
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NTSC is 60Hz (actually 59.94Hz)
PAL/SECAM is 50Hz
Cinema is 48Hz
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Basic Digital Video Concepts
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Movie length (long time Srtreaming)
Frame size (320x240)
Frame rate (30 fps for TV and 15 fps for web)
Quality (control by compression)
Color bit depth (24 bit)
Data rate (bit rate)
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It can be calculated by dividing the size of the file (in K) by
the movie length (in seconds).
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E.g. the video file size is 1.9MB  1900K
Play 40 seconds long, Data rate = 47.5K/sec
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Calculate space requirements of Video
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NTSC video (640 x 480 and 29.97 fps)
 Frame size = ([Pixel width x pixel height x bit
depth]/8)/1024
 E.g. 200KB/Frame : 6.0 MB/sec
 200KB x 30 fps = 6000KB/s, 6 MB/sec
PAL video (768 x 576 and 25 fps)
 E.g. 200KB/Frame : 5.0 MB/sec
 200KB x 25 fps = 5000KB/s, 5 MB/sec
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Frame Difference
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Science
23 Dept.
CSC1720 – Introduction
to Internet
All copyrights
reserved by C.C. Cheung 2003.
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Flash & Shockwave
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Advantages:
 File sizes are small
 Image quality is high
 It uses streaming technology
 It uses high-quality streaming audio
 It is scriptable
Disadvantages:
 A plug-in player is required
 Expensive authoring software
 Problems on printing their content
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Video Quality Evaluation
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PSNR (Peak Signal to Noise Ratio)
MSE (Mean Square Error)
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Video Processing
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Video Frame Extraction
Video Histogram
Video Filtering
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Low pass
High pass
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Group Discussion
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