1. Information Systems Design and Development Media Types Computing Science

2. Learning Outcomes Need for Compression lossy and lossless compression sound compression graphic compression video compression

3. Need for compression Sound, graphic and video files are very large The larger the file the longer it takes to download or stream over the Internet Large web pages take longer to load leading to users clicking away from page Storage capacity quickly filled by very large files

4. Possible effects of compression Reduced size of file Possible reduction in quality of files e.g. blurry pictures or less sharp sound Processor time taken up in compression and decompression

5. Lossy and lossless compression Lossy compression reduces file size by removing information from file and then compresses Lossless compression does not remove information before compression

6. Lossy and lossless compression In lossy compression once the file has been compressed you cannot reverse the process and return to the original file Lossless compression can be reversed to return to the original file

7. Lossy compression

8. Lossless compression

9. Sound compression Factors affecting size of sound files The length of the recording - the longer the recording the more information there is to be stored. The sampling depth - the number of bits used to store a sound sample. The sampling frequency - how many times per second that a sound is sampled

10. Sound compression Methods to reduce file size Reduce length of recording – part of file removed Reduce sampling depth – lowers quality Reduce sampling frequency – lowers quality

11. Sound compression Typical file type for uncompressed sound – wav Typical file type for compressed sound – mp3 ( lossy technique) Lossless techniques exist but reduce file sizes by much less than lossy for sound

12. Graphic compression Factors affecting the size of graphic files Size of image Colour depth resolution

13. Graphic compression Methods to reduce the size of graphic files without compression Crop image – remove part of image Reduce colour depth – number of colours available decreases Reduce resolution – number of pixels reduced

14. Graphic compression Different file types can apply compression Bitmap (bmp) – uncompressed but can reduce colour depth Gif – lossless compression using 8 bit colour depth JPEG – lossy compression using 24 bits (true colour) – amount of compression can be reduced

15. Graphic compression Different file types can apply compression PNG – lossless compression using 24 bit colour depth TIFF – lossless method where you can choose to have compression or not

16. Video compression Factors affecting video file size The resolution Length of film Frame rate Frame size (height and width)

17. Video compression Methods to reduce the size of video files without compression Reducing the resolution – decreasing the number of pixels used to display the image Reducing the length of film – removing sections of the film completely Reducing the frame rate – lowering the number of frames shown per second Reducing the frame size (height and width) – making the picture smaller

18. Video compression Uncompressed file types Avi Wmv Compressed file types Mp4