CSI_Chapter3:Data Representation
课程学习 CSI 所有文稿
书都积尘了，我的天
要把Markdown编辑算进娱乐时间还是学习时间呢……
0.Goals
- analog and digital data
- data compression ratios
- binary formats for numeric values
- ACSII and Unicode
- text compression
- sound representation
- RBG colors
- raster and vector graphics
- temporal and spatial video compression
1.Data and Computer
Analog and Digital Data
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2.Numeric Data Representation
Signed-Magnitude Representation
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3.Text Representation
1.ASCII Character Set
ASCII American Standard Code for Information Interchange.
- History 7 bits to represent data ( allow for 128 unique characters ) while eighth bit used as a check bit -->8 bits to represent, formlly called the Latin-1 Extended ASCII character set ( allow for 256 characters )
2.Unicode Character Set
It has a much stronger international influence for the limitation of ACSII, which only supports English.
- international
- 16 bits
- superset of ASCII
3.Text Compression
1. Keyword encoding
Keyword encoding Replacing a frequently used word with a single character
Example :
| Word |
Symbol |
| as |
^ |
| the |
~ |
| and |
+ |
2. Run-length encoding
Run-length encoding Replacing a long series of a repeated character with a count of the repetition
Example :
AAAAAAA would be encoded as *A7 , used ' * ' as flag .
3. Huffman encoding
Huffman encoding Using a variable-length binary string to represent a character so that frequently used character have short codes.
- How to create a Huffman tree
the character or node has the least time to become brother of current node , while only leaf node can represent a character
4.Audio Data Representation
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5.Images and Graphics Representation
1. RBG colors
- form a three-dimensional color space
Color depth the amount of data used to represent a color (number of bits)
- HiColor
- 16-bit color depth , 5 bits used for each RGB value , 1 bit to represent transparency
透明度.
- TrueColor
- 24-bit color depth , each value with 8 bits gives the range of 0 to 255 , resulting in the ability to represent more than 16.7 million colors.
2.Raster graphics
Raster graphics Storing image information pixel by pixel
Resolution The number of pixels used to represent a picture
- Formats of raster graphics
- bitmap file ( BMP )
- GIF ( Graphics Interchange Format ) : each GIF image can be made up of a different set of ( only ) 256 colors , called indexed color
- JPEG : a greater compression than GIFs
- PNG : a greater compression than GIFs
3.Vector graphics
Vector graphics Representation of an image in terms of lines and shapes
- The file sizes of the images , such as the number of items in the picture , determines the file size .
- not good for representing real-world images (JEPG)
- Formats of vector graphics
- Flash : most popular format used on the Web
- SVG ( Scalable Vector Graphics ) : under development , expressed in plain text
6.Videos Representation
Video codec 视频编解码器 Methods used to shrink the size of a movie
1.Temporal video compression
Temporal video compression Movie compression technique based on differences between consecutive frames 连续帧
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2.Apatial video compression
Spatial video compression based on the same compression technique used for still images
待填坑
写完之后发现，基本无法预知可读性啊 ——2019.1.11
