- Data compression involves encoding information using fewer bits that the original representation
- Two types of compression
- Lossless
- Reduces bits by identifying and eliminating statistical redundancy
- Lossy
- Reduces bits by identifying marginally important information and removing it
- Formally known as source-coding
- Helps reduce resource usage (ex. Data storage space, transmission capacity)
- Theoretical background
- Lossless – Information Theory
- Lossy – rate-distortion theory
"Data Compression Basics"
- Part 1: Lossless Data Compression
- Fundamental idea behind data compression is to take a given representation of information and replace it with a different representation that takes up less space, from which the original data can later be recovered
- If the recovered information is guaranteed to be exactly identical to the original, then the compression method is described as “lossless”
- A simple lossless compression algorithm is “run-length encoding” (RLE)
- Replaces long runs of characters with a single character and the length of the run
- Lempel-Ziv compressor family
- Entropy coding
- Assigns codes to blocks of data in a way that the length of the code is inversely proportional to the statistical probability of the block of data
- Prediction and error coding
- Part 2: Lossy Compression of Stills and Audio
- important to distinguish data from information
- fundamental idea behind lossy compression is preserving meaning rather than preserving data
- by allowing for some deviation from the source data when encoding patterns, lossy compression greatly reduces the amount of data required to describe the “meaning” of the source media
- lossy compression is ideally applied to information that is meant to be interpreted by a reasonably sophisticated “meaning processor”(human, image recognition software, etc.) that looks at a representation or rendering of the data rather than the data itself
Edward A. Galloway. “Imaging Pittsburgh: Creating a Shared
Gateway to Digital Image Collections of the Pittsburgh Region.”
- The main focus of the project was to create a single Web gateway for the public to access thousands of visual images held in the collections of the Pitt Archives Service Center, CMOA, and the Historical Society of Western PA
- The content partners were responsible for selections of collections/images, describing/cataloging images, digitization, and delivering images/metadata to DRL
- DRL was responsible for providing access to the image collections via DLXS middleware
- Characteristics of the Web gateway
- Conduct keyword searches across all image collections
- Browse images
- Read about the collections and their contents
- Explore images by time/place/theme
- Order image reproductions
- Communication challenges
- Selection challenges
- Metadata challenges
- Project-wide vs local needs
- Workflow challenges
- Website development challenges
I was not able to access "Youtube and Libraries: It Could be a Beautiful Relationship" by Paula L. Webb.
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