Communication outline

Topics: Frame rate, NTSC, Camera Pages: 5 (744 words) Published: October 15, 2014
Com 261 Lesson 02

Video signal color
A video signal color is made up of Red, Green and Blue colors on the spectrum.

Scanning process
1. Interlaced scanning
2. Progressive scanning

Interlaced scanning
1. Frame=field 1+field 2
A field is an odd or even vertical line of video.
2. Refresh rate=the number of frames scanned each second , fps.(每秒钟扫过的frame数)

Progressive scanning
All vertical lines are shown with each scanning cycle.

Aspect ratio (画面长宽比)
1. Width to height of the tv screen
2. Standard TV: 4*3
3. HDTV: 16*9

All digital systems are based on the off/on principle of binary code. 1. On state=1
2. Off state=0

Sampling
1. A number of voltages are taken a different interval. Sampling is basically analyzing the analog video. 2. The higher number of instances at short intervals gives a high sample rate. 3. Higher sampling rate=better images.

4. 在同一个short interval中,sample越多,图像越逼真。 如同每秒16次sample比每秒8次更逼真

Compression 压缩
Compression is the temporary rearranging or eliminating of all data that is not necessary to maintain the quality of video or audio for transport or storage. 1. Lossless compression=dosen’t throw away any info, just rearrange it. 2. Lossy compression=eliminates any info that is redundant (can reduce image quality). 例子:MP4

3. Codecs=compression/decompression systems that change the ways files compressed.

Compression
1. Downloading
The info is packaged out of order and must take time to assemble before you can view or listen to it. 2. Streaming
The info is in order and therefore you can view/listen to the first part of the file while the rest is still being delivered.

Frame rates
1. =the number of frames scanned per second
2. can be changed in digital video
3. Film: 24 fps (realness小)
4. Video: 30fps (realness大)
5. Some cameras can shoot a variety of frame rates.

Flat panel displays
1. LCD Screen (Liquid crystal display)
Uses a thin layer of liquid with crystal molecules that change when a video beam hits them. 2. Plasma Screen (等离子电视)
Uses a thin layer of gas that changes when video beam hits it. RGB pixels arranged much like a standard TV
3. LED Screen (Liquid-emitting diodes 液体发光二极管) A cluster of red, green and blue diodes that are together to form a whole pixel.

Basic camera functions
1. Lens
2. Imaging device (光学信号转换为电子信号)
3. Viewfinder (画面检测器)

Lens 焦距小,视野宽,照片容纳范围广。
1. Focal lens =a technical measure of distance from the iris inside the lens to the plane where the projected image is in focus. (光聚集点到成像面的距离) 2. Wide angle lens=广角镜,呈像范围广,focal length短 Narrow angle lens=窄角镜,

Zoom lens=change from short fl to longer fl (zoom in/out)
3. Zoom range/ratio=how close a view you can get when zooming from the widest angle to the most telephoto angle Digital zoom magnifies the image to give a perceived zoom (实际上pixel数量相同,只是放大原图一部分) 4. Lens iris

Iris controls the amount of light transmitted through the lens 5. Aperture光圈=the hole that the light passes through
F-stop
=how much light is transmitted through the lens
=Focal length焦距/effective aperture diameter有效光圈直径 6. Lens speed
Fast lens=lower f-stop例子:f/1.2或f/1.4
Slow lens=higher f-stop例子:f /4.5
Fast lens can produce better pictures in low light?

Image device or sensor
1. CCD (Charged coupled device)=an imaging device that translates optical images into electrical energy (RGB). 将光学图像解读为电子能量 2. Resolution=the sharpness of the picture, affected by the number of pixels on the CCD

Signal processing
1. Luminance channel (Y)亮度=the black and white parts of the video, responsible for picture sharpness? 2. Chrominance channel (RGB)色度=color parts
3. NTSC= National Television System Committee

Viewfinder
Viewfinder is essentially a small monitor attached to the camera. It combines the Y and C channels and reconverts video signal to video picture.

Types of cameras
1. Camcorder=portable camera and recorder in 1 unit.
2. ENG/ENP camera=portable camera that does not have a recorder built...
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