Soft test preparation multimedia system

One 、 Multimedia Basics

1、 The classification of media

（1） Feeling media （Perception Medium）
（2） Presentation media （Representation Medium）
（3） Performance media （RPresentation Medium）
（4） Exchange media （Interchange Medium）： Storage media and transmission media
Multimedia technology refers to the use of computer technology to transform text 、 Images 、 graphics 、 voice 、 Animation, television and other media are integrated , Make logical connection between various information , And they can be acquired 、 Compress 、 Processing 、 Storage , Integrated into an interactive system .

2、 voice

1、 The process of digitizing sound signals
（1） sampling ： Acquiring the amplitude of the sound signal at some specific time is called sampling .
Sampling period ： Sampling interval
Mining frequency ： The reciprocal of the time interval
In order to reconstruct the frequency components of all original signals , The sampling frequency needs to be greater than twice the highest frequency of the sound signal .
（2） quantitative ： Measure the amplitude of the sample A/D transformation （ A / D conversion ）, Quantized and expressed in binary .
Quantization accuracy （ Quantization resolution ）： The number of binary digits reflects the accuracy of measuring the amplitude of sound waveform
（3） code ： Data coding according to certain format requirements , Then organize the data into files according to a specified format .
2、 The expression of sound （ Calculation formula ）
Data transfer rate （bps）= sampling frequency （Hz）* Quantization Bits （bit）* Track number
The amount of sound signal data （Byte）= Data transfer rate （bps）* The duration of the （s）/8

3、 Graphics and images

1、 Basic concept of color
Three elements of color ： tonal 、 Saturation and brightness
Color model ：RGB Color model 、CMY Color model 、YUV Color models
2、 Resolution and pixel depth
（1） The resolution of the
Display resolution ： The number of pixels that can be displayed on the display
Image resolution ： Refers to the pixel density of an image , The size of the digitized image is expressed in dots per inch .
（2） Pixel depth
The more bits of a pixel color , The more colors or gray levels he can represent , The deeper the pixel depth .
3、 Image acquisition
sampling —— quantitative —— code
4、 Graphic image conversion
1、 Use rasterization （ Rasterize ） Technology can convert graphics into images ;
2、 Image can be transformed into graph by using graph tracking technology ;
3、 Graphics and images are stored in computer memory in the form of files , It can also be applied 4、 The software realizes the conversion between file formats , Achieve the conversion between graphics and images .
5、 Graphics compression coding and standards
Calculation formula of image data amount ：
Total image pixels = Horizontal pixels of the image * Vertical pixels of the image
Amount of image data = Total image pixels * Image depth /8（B）
（1） lossless compression
The data before compression and after decompression are completely consistent . Common techniques are ： Entropy coding technology 、 Travel coding technology 、 Lossless predictive coding technology 、 Dictionary coding technology, etc .
（2） Lossy compression
Unrecoverable information is lost during compression , However, the compression coding of multimedia information allows certain information distortion .

4、 Animation and video

1、 Real time animation and vector animation
Real time animation uses various algorithms to control the motion of moving objects ;
Vector animation is an animation form derived from vector graphics ;
2、 3D animation and 2D animation
Two dimensional animation is an improvement of traditional animation , The main technologies are image technology and graphics technology , Image technology is used to draw key frames 、 Picture overlay 、 The data generated , Graphic technology is used for automatic or semi-automatic intermediate picture generation .
three-dimensional animation ：
3 A form of recording a model of an object ：
（1） Wireframe model ： Use lines to describe a body ;
（2） Surface models ： Use the combination of faces to describe the shape ;
（3） entity model ： Decompose a complex shape into several basic shapes ;

Two 、 Common multimedia file format types

1、 Sound file format

Sound file format	explain
Wave file （.wav）	Windows Standard audio file formats used in the system
Sound file （.snd）	NeXT Computer The company to launch , Support compression
Audio file （.au）	be applied to UNIX Sound file format in the system
AIFF file （.aif）	Apple company Mac OS Standard audio file format in
Voice file （.voc）	It consists of file header block and audio data block
.mp3 file	Popular sound file formats , High compression ratio
RealAudio file （.ra）	It has strong compression and minimal distortion
MIDI file （.mid/.rmi）	Non waveform sampling point music format

2、 Image file format

Image file format	explain
BMP file （.bmp）	Windows Bitmap image file format adopted by the system
GIF file （.gif）	Storing image related information in data blocks
TIFF file （.tif）	A general image file format developed for scanners and desktop publishing systems
PCX file （.pcx）	use RLE Run length encoding , The file body stores the compressed image data
PNG file （.png）	GIF substitute , Support lossless data compression
JPEG file （.jpg）	It is suitable for processing a large number of images , Is a lossy compressed still image file storage format
WMF file （.wmf）	Use only in Windows in , Save the function call information

3、 Video file format

Video file format	explain
Flic file （.fli/.flc）	2D/3D Color animation file format used in animation software
AVI file （.avi）	accord with RIFF File specification for digital audio and video file formats
Quick Time file （.mov/.qt）	Apple Company developed audio 、 Video file format
MPEG file （.mpeg/.mpg/.dat/mp4）	stay PC There is a unified standard format on , Compatibility is good.
Real Video file （.rm/.rmvb）	A streaming video file format