Multimedia Technology,
Chapter 5, Digital and Analog Video
Topics Covered
- Video
- Analog Video
- Video Signals
- NTSC,
- PAL,
- SECAM,
- Digital Video
- Analog to Digital Conversion
- Sampling and Quantization
- HD Video
- Compression,
- Chroma Sampling
- Creating and Shooting Video
VIDEO
Video uses Red-Green-Blue color space, Pixel resolution (width x height), number of bits per pixel, and frame rate are factors in quality, But there’s much more to it.
A video can be decomposed into a well-defined structure consisting of five levels
1. Video shot is an unbroken sequence of frames recorded from a single camera. It is the building block of a video.
2. Key frame is the frame, which can represent the salient content of a shot.
3. Video scene is defined as a collection of shots related to the video content, and the temporally adjacent ones. It depicts and conveys the concept or story of a video.
4. Video group is an intermediate entity between the physical shots and the video scenes. The shots in a video group are visually similar and temporally close to each other.
5. Video is at the root level and it contains all the components defined above.
Multimedia Technology - Chapter 5_ Video
A video can be decomposed into a well-defined structure consisting of five levels
1. Video shot is an unbroken sequence of frames recorded from a single camera. It is the building block of a video.
2. Key frame is the frame, which can represent the salient content of a shot.
3. Video scene is defined as a collection of shots related to the video content, and the temporally adjacent ones. It depicts and conveys the concept or story of a video.
4. Video group is an intermediate entity between the physical shots and the video scenes. The shots in a video group are visually similar and temporally close to each other.
5. Video is at the root level and it contains all the components defined above.
TYPES OF VIDEO SIGNALS
- Component video
- Composite Video
- S-video
COMPONENT VIDEO SIGNLS
Component video: Higher-end video systems make use of three separate video signals for the red, green, and blue image planes. Each color channel is sent as a separate video signal.
Most computer systems use Component Video, with separate signals for R, G, and B signals.
For any color separation scheme, Component Video gives the best color reproduction since there is no “crosstalk” between the three channels.
This is not the case for S-Video or Composite Video, discussed next. Component video, however, requires more bandwidth and good synchronization of the three components.
Makes use of three separate video signals for Red, Green and Blue.
COMPOSITE VIDEO | 1 SIGNAL
Composite video: color (\chrominance") and intensity (\luminance") signals are mixed into a single carrier wave. Chrominance is a composition of two color components (I and Q, or U and V).
- Used by broadcast TV, In NTSC TV, e.g., I and Q are combined into a chroma signal, and a color subcarrier is then employed to put the chroma signal at the high-frequency end of the signal shared with the luminance signal.
- The chrominance and luminance components can be separated at the receiver end and then the two color components can be further recovered.
- When connecting to TVs or VCRs, Composite Video uses only one wire and video color signals are mixed, not sent separately. The audio and sync signals are additions to this one signal.
- Since color and intensity are wrapped into the same signal, some interference between the luminance and chrominance signals is inevitable.
S-VIDEO | 2 SIGNALS
S-Video: as a compromise, (Separated video, or Super-video, e.g., in S-VHS) 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.
- In fact, humans are able to differentiate spatial resolution in grayscale images with a much higher acuity than for the color part of color images.
- As a result, we can send less accurate color information than must be sent for intensity information | we can only see fairly large blobs of color, so it makes sense to send less color detail.
ANALOG VIDEO
An analog signal f(t) samples a time-varying image. So called “progressive” scanning traces through a complete picture (a frame) row-wise for each time interval.
In TV, and in some monitors and multimedia standards as well, another system, called \interlaced" scanning is used:
a) The odd-numbered lines are traced first, and then the even numbered lines are traced. This results in “odd” and “even” fields --- two fields make up one frame.
b) In fact, the odd lines (starting from 1) end up at the middle of a line at the end of the odd field, and the even scan starts at a half-way point.
Salam Alikum Dr.Zeeshan. It is very perfect work. Thanks
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