How does black/white encoding differ from RGB?
Each pixel is encoded with either 0 (white) or 1 (black).
How is the greyscale encoded?
- 8 bits can be used to represent 256 different shades of gray
- 0 (black) to 255 (white)
How are color images encoded?
16 colors (4 bits per pexl)… use a color palette
256 colors (8 bits per pixel)
RGB True Color (Red Value, Green Value, Blue Value)
- Typically 8 bits per color (total of 24 bits per pixel)
- 16.7 million different colors.
Define:
Vector Graphics
All components of the image are stored
Can be easily scaled without losing image quality
Common Vector Formats
- Adobe Illustrator
- CorelDRAW
- MathML
Define:
Data Compression Algorithms
Attempt to represent information in ways that preserve accuracy while using significanlty less space.
Define:
Compression Ratio
Measures how much compression schemes reduce storage requirements of data.
Define:
Run-length Encoding
Replaces a sequence of identical v1, v2,…,vn by a pair of values (v, n).
Define:
Variable Length Code Sets
- Often used to compress text
- More efficient
- Can also be used with other forms of data.
Define:
Lossless Compression Schemes
- No information is lost in the compression
- It is possible to exactly reproduce the original data.
Define:
Lossy Compression Schemes
- Do not gaurantee that all of the information in the original data can be fully and completely recreated
- Trade image quality for file size
Which are the common Raster Image File Formats?
JPEG (Joint Photographic Experts Group)
- 8 bit grayscale, 24 bit color
- Compression is lossy
TIFF (Tagged Image File Format)
- 8 bit or 16 bits per color
- Compression can be lossy or lossless
GIF (Graphics Interchange Format)
- 8 bit color palette
- LZW lossless compression
- Is now patent-free
BMP
- Uncompressed, large, lossless, simple structure
PNG (Portable Network Graphics)
- Free open-source alternative to GIF
- 8 bit color palette, 24-bit truecolor, 48-bit true color
- Compression is lossless
- Patent-free replacement for GIF
Why is binary representation reliable?
Computers use binary representation for reasons of reliability.
Building a base-10 “decimal computer”
- Requires finding a device with 10 distinct and stable energy states that can be used to represent the 10 unique digits (0,1,….,9) of the decimal system.
Bistable Environment
- Only two (rather than 10) stable states separated by a huge energy barrier.
What is the universal storage medium?
- No practical universal storage medium exists
- All forms of storage have drawbacks
- Computer systems contain several kinds of storage
Describe the storage hierarchy.
Primary
- Directly accesible to the CPU
- Relatively expensive
- RAM (volatile) … access time in nanoseconds
- ROM (non-volatile)
- Contains a small startup program (BIOS)
- Reads a larger program from non-volatile secondary storage to RAM and start to execute it.
Secondary
- Not direclty acessible by the CPU
- Relatively cheap
- Non-volatile
What are the types of secondary storage mediums?
Hard disk drives … access time in milliseconds
Rotating optical storage devices
- Longer access times than hard disk drives
- CD drive
- DVD drive
Flash Memory
- USB Flash drives
- SD cards
- Memory Stick (Sony)
Solid State Drives
Hybrid Drives
Describe virtual memory
- As primary memory fills up, the least-used data is moved to secondary storage devices (swap file)
- This data is retrieved when needed
- More retreivals mean overall system performance is degraded
Describe offline storage
- Storage that can be physically removed or disconnected
- Inreases general information security
- Useful for archiving data
What are the seven characteristics of storage?
- Volatility
- Mutability
- Accessibility
- Addressability
- Capacity
- Performance
- Energy Use
Define:
Non-volatile Memory
- Retain stored information without power
- Suitable for long-term storage
Define:
Volatile Memory
Requires constant power to maintain stored information
Types
- Dynamic Random-Access Memory (DRAM): requires stored information to be preriodically re-read and re-written (refresh) or it will be lost
- Static Random-Access Memory (SRAM): does not need to be refreshed as long as power is applied.
Define:
Mutable Storage
Read/Write Storage
- Allows information to be overwritten at any time
- Example: RAM, hard disk drives
Define:
Immutable Storage
Read Only Storage
- Retains information stored at the time of manufacture
Write Once Storage
- Allows information to be written only once at some point after manufacture
- Example: CD-R
Define:
Slow Write, Fast Read Storage (Mutability)
Allows information to be overwritten multiple times, but with the write operation being much slower than the read operation.
- Example: CD-RW and Flash Memory
Define:
Random Access
- Any location in storage can be accessed at any moment in approximately the same amount of time
- Most semiconductor memories and disk drives provide random access.
