1. Web Design and Development
Design – Standard File Formats

2. Learning Intention
I will learn about standard file formats for audio and image files.

3. Compression
File compression is the process of reducing the size of a file.
Why is compression needed?
to reduce space taken on backing storage
to shorten time to send a file between two computer systems

4. Types of Compression
Lossless (no loss) compression does not affect the quality of the file
Lossy compression:-
results in a file of poorer quality than the original
results in smaller files than lossless compression
can result in artefacts (flaws) appearing in JPEGs

5. Artefacts – flaws due to compression

6. Standard File Formats
Standard File Formats are used to store files so that the files can be used in a different application package from the one which created it.

7. Graphics Files – GIF Graphics Interchange Format
Compressed using lossless compression
GIF files may be interlaced – low quality version can be shown while rest of file downloads

8. Graphics Files – GIF (cont)
Supports animation - multiple images in one GIF file
Supports one transparent (see through) colour
Colour depth of 8-bit (256 colours)
Good for cartoon like images

10. Graphics Files – PNG Portable Network Graphics
Includes all the advantages of GIFs but without the limitations
No animation
Uses lossless compression
24 bit colour depth
Allows partial transparency

11. Graphics Files - JPEG Joint Photographic Expert Group
Lossy compression – amount of compression is adjustable – allows higher quality but takes more storage
good for natural real life images (photos)
Does not support transparency or animation
Supports up to 16.7 million colours (24-bit colour depth)

12. Bitmap Graphics GIF, PNG and JPEG are all bitmap graphic formats.
Each pixel in the image is stored as a set of bits representing the colour.
E.g. 256 colour = 8 bits per pixel (28=256) so each pixel colour stored as a binary digit from to

13. Graphics File Formats - Summary
JPEG
GIF
PNG
Compression
lossy
lossless
Animation no
yes
Transparency no
one colour
partial transparency
Colour Depth
24-bit
16,777,216
8-bit
256 colours

14. Graphics Files – SVG Scalable Vector Graphics
Stores objects (line, rectangle, polygon, ellipse) as a list of attributes e.g. fill colour, line colour, co-ordinates
No compression
Does not lose quality when scaled
Supports layers

15. Factors Affecting Graphic File Size & Quality
resolution (no. of pixels)
higher resolution = better quality
= bigger file size
colour-depth (no. of bits per pixel)
higher colour depth = better quality

16. Audio Sound is analogue
Computer changes it to digital by sampling (measuring the sound wave and storing the measurement as a digital number)
The sampling rate is the number of times per second that the sound wave is measured
CD quality sound is sampled at 44.1KHz = 44,100 time per second

17. Factors Affecting Sound File Size
Sampling rate
higher sampling rate = better quality
= bigger file size

18. Audio Files - WAV WAVeform audio file format
WAV is the standard format for storing sound files on Windows systems.
Uncompressed, therefore large file size
Used for high quality sound

19. Audio Files – MP3 Created by Motion Pictures Expert Group
MP3 is a file format for compressing sounds
CD quality sound
Uses lossless compression
removes sound human ears cannot hear
removes quiet sounds when a loud sound happens at the same time
file size reduced to 10% of original size

20. Success Criteria
I can compare standard audio and video file formats.
I can describe the factors affecting file size and quality.