File formate and multimedia

Question 1

File formate

Answer 1

Text file - which contain readable text ex. word-format or XML-format

• can be edited and viewed on almost every computer
• difficult when different international character sets (ÅÄÖ, chinese etc.) -> the most important is ASCII
• HTML (most famous tagged language) - simplified for of SGML (standardized general mark-up language) ex. …. –> documentation purposes
• XML - more general form of HTML, central documentation platform
• PARSING - convert the text file into the internal data structure

Binary file - which is not reachable without any interpreting application
- some data structure (RGB colors) are difficult to be stored in a text file and for the compression reason

Question 2

Compression

Answer 2

• to optimizing the available memory
• compression rate should be very high (compressed data should be very good) and the decompressed data should be very good (good accurancy) + the complexity of the algorithm should be low to be fast and simple compress/decompress
• Types: lossy (reduction of irrelevance - source encoding) and loss-free (reduction of redundancy - entropy encoding = > amount of info in a set of characters), Hybrid compression (both lossy and loss-free), image compression (JPEG,MPEG)

Question 3

Lossy compression

Answer 3

• not reversible
• removes barely visible/contain little information
• some disavantage: noise, lack of definition, loss of color, changes in contrast, brightness, geometric distortions

LEMPEL-ZIV-WELCH (LZW)
- Buffert table

Question 4

Loss-free compression

Answer 4

• is reversible
• the original data is kept, removes repeated data (area with same color)

RUN-LENGTH ENCODING: does not exceed a compression with factor 3 –> plays a minor role in compression of videos.
- only suitable for computer-generated data (image data), written text changes frequently -> not containing a long sequence of identical symbols.
Ex 4A3B2C1A FOR AAAABBBCCA

HUFFMAN

• probability three and entropy, H
• lower H lower bites – better
• PREFIX FREE

Question 5

Audio data

Answer 5

• the sound pressure level and the sound frequency
• analog: directly recorded on magnetic tapes/discs
• digital: converted first into a binary signal by analog-digital converter. Benefit: lower noise and higher dynamic range, copies can be made without any losses
• DIGITALIZATION PROCRESS: 1. sampling –> 2.quantization (complete interval of the measurement value,y-axis is split up into certain amount of sub-intervals)–> 3.Encoding –> 4.PCM

Question 6

BMP

Answer 6

Bitmap Pictures - data length in bytes

• it can be output on any screen or printer
• but it is large files, because does not uses any compression (sometimes RLE)
• based on RGB-model

Question 7

GIF

Answer 7

• good compression without any losses

Question 8

MPEG

Answer 8

• DCT (discrete cosinus transformation): removes high frequency –> softer images