1.3.1 (a) + (b)Compression

Lossy vs Lossless, RLE + Dictionary Based-Compression

What is compression?

the process used to reduce the file size (reduces storage space required to store the file)

Why is compression important when sharing files over networks/the internet?

larger files = longer to transfer

What is lossy compression?

the process of reducing file size while also removing unnecessary data

What is lossless compression?

the process of reducing file w/o losing any data

Where is lossy compression used?

• images - JPEG

• audio files - MP3

Where is lossless compression used?

• high resolution images - PNG

• text documents - ZIP

From what type of compression can the original file be recovered?

lossless compression

What is run length encoding (RLE)?

lossless compression - repeated data values with:

• a single value

• the number of occurrences

e.g.

OG data: AAARRRRRRWWWW

Compressed data: 3A6R4W

What are advantages of run length encoding (RLE)?

• simple & efficient - for data w/ repeated values

• lossless - og data can be reconstructed

• fast & easy to implement - algorithms easy to execute

What are disadvantages of run length encoding (RLE)?

• inefficient for data w/ few repeated values

• limited application - only effective for certain types of data (e.g. B&W images,simple graphic files)

What is Dictionary Based Compression?

replaces repeated patterns of data with shorter codes from a dynamically built dictionary

e.g. OG data: ABABACABAC

dictionary: AB=1; AC=2;

compressed data: 11212

What are advantages of Dictionary Based compression?

• efficient for larger data sets - effective compression

• scalable - better for complex data (than RLE) w/ varied repetitions

• widely used in formats like ZIP & PNG

What are disadvantages of Dictionary Based compression?

• requires more processing power - building & managing dictionary is more computationally intensive

• ineffective for very small files - dictionary may not reduce file size enough to offset dictionary’s own storage