Soft test preparation multimedia system

1. Basic knowledge of multimedia

1. Classification of media

(1) Perception Medium
(2) Representation Medium
(3) Representation Medium (RPresentation Medium)
(4) Interchange Medium: Storage media and transmission media
multimedia technology refers to the use of computer technology Text, images, graphics, sound, animation, television and other media are integrated to establish a logical connection of a variety of information, and can obtain, compress, process, and store them, and integrate them into an interactive system.

2. Sound

1. The digitalization process of the sound signal
(1) Sampling: Obtaining the amplitude of the sound signal at certain specific moments is called sampling.
Sampling period: the time interval
of sampling. Frequency: the reciprocal of the time interval.
In order to be able to reconstruct all the frequency components in the original signal, the sampling frequency needs to be greater than twice the highest frequency of the sound signal.
(2) Quantization: A/D conversion (analog-to-digital conversion) is performed on the amplitude of the sample, and the quantization is expressed in binary.
Quantization accuracy (quantization resolution): The number of binary digits reflects the accuracy of measuring the amplitude of the sound waveform
(3) Coding: Data is encoded according to certain format requirements, and then the data is organized into files according to a certain format.
2. Sound representation (calculation formula)
data transmission rate (bps) = sampling frequency (Hz) * quantization bit (bit) * number of channels
sound signal data volume (Byte) = data transmission rate (bps) * duration ( s)/8

3. Graphics and images

1. The basic concept of
color. The three elements of color: hue, saturation and brightness.
Color model: RGB color model, CMY color model, YUV color model
2. Resolution and pixel depth
(1) Resolution
Display resolution: Can be displayed on the display The number of pixels displayed.
Image resolution: refers to the density of pixels that make up an image. The number of dots per inch represents the size of the digitized image.
(2) Pixel depth
The more the number of bits in a pixel color, the more colors or gray levels it can represent, and the deeper the pixel depth.
3. Image acquisition
Sampling-quantization-coding
4. Graphics and image conversion
1. Using rasterization (dot matrix) technology to convert graphics into images;
2. Using graphics tracking technology to convert images into graphics;
3. Graphics and images are stored in the computer memory in the form of files, and the conversion between file formats can also be realized through applications. 4. The conversion between graphics and images can be achieved.
5. Graphic compression coding and standards
. The calculation formula for the amount of image data:
total image pixels = horizontal pixels of the image * vertical pixels of the
image Image data volume = total pixels of the image * image depth/8 (B)
(1) Lossless compression
The data before compression and after decompression are exactly the same. Common technologies include: entropy coding technology, run length coding technology, lossless predictive coding technology, dictionary coding technology, etc.
(2) Lossy compression
In the compression process, there is unrecoverable information loss, but the compression coding of multimedia information allows a certain amount of information distortion.

4. Animation and video

1. Real-time animation and vector animation
Real-time animation uses a variety of algorithms to realize the motion control of moving objects;
vector animation is an animation form derived from vector graphics;
2. Two-dimensional animation and three-dimensional 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, screen overlays, and data generation, and graphics technology is used to generate automatic or semi-automatic intermediate images.
Three-dimensional animation:
3 forms to record the model of an object:
(1) Wire frame model: Use lines to describe a shape;
(2) Surface model: Use a combination of faces to describe the shape;
(3) Solid model: combine a complex The body of is broken down into several basic bodies;

2. Commonly used multimedia file format types

1. The format of the sound file

Sound file format	Description
Wave file (.wav)	Standard audio file format used in Windows system
Sound file (.snd)	NeXT Computer company launched, supports compression
Audio file (.au)	Sound file format used in UNIX system
AIFF file (.aif)	Standard audio file format in Apple's Mac OS
Voice file (.voc)	Composed of file header block and audio data block
.mp3 file	Popular sound file format with high compression rate
RealAudio file (.ra)	With strong compression and minimal distortion
MIDI file (.mid/.rmi)	Non-waveform sample point music format

2. Image file format

Image file format	Description
BMP file (.bmp)	Bitmap image file format adopted by Windows system
GIF file (.gif)	Use data blocks to store image related information
TIFF file (.tif)	A universal image file format developed for scanners and desktop publishing systems
PCX file (.pcx)	Using RLE run length encoding, the file body stores the compressed image data
PNG file (.png)	Alternative to GIF, support lossless data compression
JPEG file (.jpg)	Suitable for processing a large number of images, it is a lossy compressed static image file storage format
WMF file (.wmf)	Only used in Windows, it saves function call information

3. Video file format

Video file format	Description
Flic file (.fli/.flc)	Color animation file format used in 2D/3D animation production software
AVI file (.avi)	Digital audio and video file formats that comply with the RIFF file specification
Quick Time file (.mov/.qt)	Audio and video file formats developed by Apple
MPEG files (.mpeg/.mpg/.dat/mp4)	There is a unified standard format on the PC, with good compatibility
Real Video file (.rm/.rmvb)	A streaming video file format