Unit 1 Lossless Compression, Lossy Compression

1. NADAR SARASWATHI
COLLEGE OF ARTS
AND SCIENCE
SUBJECT: DATA COMPRESSION
TOPIC: LOSS LESS COMPRESSION,
LOSSY COMPRESSION
R. Girisakthi
II M.sc Computer
Science

2. LOSS LESS COMPRESSION
Lossless compression reduces file size by removing
unnecessary metadata without any discernible loss in picture
quality. The original data can be perfectly reconstructed after
decompression.
Advantages of Lossless Compression:
 No Quality Loss: Lossless compression maintains original
quality during compression and decompression.
 Suitable for Text and Archives: Ideal for text-based files,
software installations, and backups.
 Minor File Size Reduction: Reduces file size without
compromising quality significantly.

3. Disadvantages of Lossless Compression:
 Larger Compressed Files: Compared to lossy
formats they compressed larger files.
 Less Efficient for Multimedia: Not as effective for
multimedia files.

4. LOSSLESS COMPRESSION FILE
TYPES
There are various file types across image, audio and video
formats that use
lossless compression. Here are a few of the most common
examples:
 PNG - This is a pixel-based image format that offers high-
quality graphics. PNG files are a popular choice for
graphic designers as it supports transparent backgrounds,
which are ideal for online logos and illustrations.
 BMP - Another image file type used for storing and printing
high-quality digital photos. BMP files are now compatible
with most Mac and Android devices.

5.  RAW -These powerhouse files are one of the most common
camera image formats. RAW files capture a very high level of
detail and contain unprocessed image data — ready to edit,
export or compress into another file format.
 GIF - This popular web staple stands for Graphics
Interchange Format and is typically known for displaying
graphics, logos and (famously) GIF animations.
 ZIP -A common archive file format used to compress files
into another location on your computer, reducing their size.
This is handy for data storage and transferring files.
 WAV - A raw audio format that can store a large amount of
uncompressed audio data, ideal for capturing high-quality
and professional audio recordings.

6. LOSSY COMPRESSION
Lossy Compression reduces file size by permanently removing
some of the original data. It’s commonly used when a file can
afford to lose some data or if storage space needs to be
significantly freed up.
Advantages of Lossy Compression
 Smaller File Sizes: Lossy compression significantly reduces
file sizes, making it ideal for web use and faster loading times.
 Widely Supported: Many tools and software support lossy
formats (e.g., JPEG for images, MP3 for audio).
 Efficient for Multimedia: Effective for compressing
multimedia files without noticeable quality loss.

7. Disadvantages of Lossy Compression:
 Quality Degradation: Due to data removal, lossy files may
exhibit reduced quality.
 Not Suitable for Critical Data: Inappropriate for situations
where data integrity is crucial.
For lossy compression, we need to measure the quality of the
decompressed data as well as the compression effect. The word
fidelity is often used to describe the closeness between the
source and decompressed file. The difference between the two,
i.e. the source before compression and the file after
decompression, is called distortion. Often approximate
distortion is used in practice. We shall look at lossy compression
performance more closely later.

8. A compression algorithm can be evaluated in a
number of different ways. We could measure the relative
complexity of the algorithm, the memory required to
implement the algorithm, how fast the algorithm
performs on a given machine, the amount of
compression, and how closely the reconstruction
resembles the original.

9. Data Loss:
 Lossy compression deliberately removes some data during the
compression process. This data is often considered unnecessary
or less important for the intended purpose of the file, such as
an image or audio file.
Irreversible:
 Once data is lost during compression, it cannot be
regained. This is a key difference from lossless compression,
where the original data is preserved during compression and
decompression.

10. File Size Reduction:
 The main advantage of lossy compression is the significant reduction in
file size. This is achieved by removing redundant or less critical
information, making files easier to store, transmit, and manage.
Quality Degradation:
 While lossy compression is effective at reducing file size, it also
introduces a degree of quality degradation. The amount of quality loss
depends on the compression algorithm and the chosen compression
settings.
Common Use Cases:
 Lossy compression is commonly used for images (like JPEG), audio
(like MP3), and video files, where a slight loss in quality is often
acceptable for the sake of storage and bandwidth efficiency.

11. THANK YOU