Media Types

Standard file formats:
- Text: txt, rtf
- Audio: wav, mp3
- Graphics: jpeg, bmp, gif, png
- Video: mp4, avi
- Pdf
Factors affecting file size and quality, including resolution, colour depth, sampling rate
Calculation of file size for colour bitmap
Need for compression

Text:
- txt – Only stores text, no formating or fonts are stored. Very small file size
- rtf – Rich Text Format, formating information and graphics are stored as text.
Audio:
- wav – uncompressed audio file format
- mp3 – Compressed audio file format
Graphics:
- jpeg – lossy compression – used for photos, small file size
- bmp – Bitmap, uncompressed, large file size
- gif – Lossless compression, only 256 colours, used for animations and clip art, supports transparency
- png – Lossless compression, Millions of colours, supports partial transparency
Video:
- mp4 – Compressed file format
- avi – Uncompressed file format
Pdf: Portable Document Format – stores all formatting information and font details so that the document looks identical on all computers.

resolution – the number of pixels used to make up the picture.
colour depth – the number of possible colours used to make up a pixel. The more possible colours the greater the file size.
sampling rate – in sound files the number of recordings taken per second., the greater the sample rate the higher the quality and file size.

Formula

Number of pixels = image width x resolution x image height x resolution

Example 1

This is enlarged but is 1 inch by 1 inch at 22 Dots Per Inch. In that case there are 22 x 1 x 22 x 1 = 484 pixels

Example 2

Bitmap with a resolution of 600×600 pixels in 8 bit colour.

Storage requirements

600 x 600 x 1 bytes = 360000 
It is 1 byte as it is 8 bits per pixel 
360000/1024 = 351.6 kilobytes

Example 3

Calculate the number of pixels in 4 inch by 5 inch photograph scanned which has a resolution of 600 dots per inch.

Pixels = 4 x 600 x 5 x 600 = 7,200,000 pixels
1pixel = 1 bit 
7,200,000 / 8 = 90000 bytes 
90000 bytes / 1024 = 878.9 Kb

Compression reduces the file size so that the web page loads more quickly. Reducing bit depth has the same impact. Quality of the image is affected.