Web Design and Development Design Standard File Formats
Web Design and Development Design – Standard File Formats
Learning Intention • I will learn about standard file formats for audio and image files.
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
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
Artefacts – flaws due to compression
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.
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
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
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
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)
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 0000 to 1111
Graphics File Formats - Summary JPEG GIF PNG Compression lossy lossless Animation no yes no one colour partial transparency 24 -bit 16, 777, 216 Transparency no Colour Depth 24 -bit 8 -bit 16, 777, 216 256 colours
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
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 = bigger file size
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. 1 KHz = 44, 100 time per second
Factors Affecting Sound File Size • Sampling rate • higher sampling rate = better quality = bigger file size
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
Audio Files – MP 3 • Created by Motion Pictures Expert Group • MP 3 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
Success Criteria • I can compare standard audio and video file formats. • I can describe the factors affecting file size and quality.
- Slides: 20