Why Reduce File Size?
- The size of a file determines:
- How much space it will require for storage
- How long it will take to transmit from one device to another
- Often file sizes need to be reduced and will use a form of compression
- The two types of compression are:
- Lossy compression - Unnecessary data is removed and can significantly reduce file sizes. This is most often used for audio, video and image
- Lossless - Allows the original data to be perfectly reconstructed from the compressed version without any loss of information or quality. This is most often used for text and document and software compression
- E.g. if 10 images were to be displayed on a website and their original size was 18MB each, with an internet connection of 32 megabits per second the webpage would take around 45 seconds to load and require 180 Mb of storage space online to host the images
- Using lossy compression it is possible to compress the files down to around 10% of their original size meaning that the same internet connection would require just 4 seconds to load the images and the storage requirement for the files would be 18MB
How are Files Compressed?
There are many different technical ways that file sizes can be reduced however some simple methods and techniques for multimedia files are below:
- Images can be compressed by the following:
- Reducing the number of colours in the image (known as the bit depth)
- Reducing the resolution of the image (the total amount of pixels that make up the image)
- Videos can be compressed by the following:
- Reducing the video resolution
- Reducing the number of video frames per second
- Sound can be compressed by the following:
- Removing frequencies that are outside of the human hearing range
Worked example
An author is writing a new textbook about ICT. He has used a large number of images in the document and wishes to send the document as an email attachment to his publisher, but the file is currently too large.
Describe how he could reduce the size of the document without reducing the number of images. [4]
The author could reduce the size of the document by either reducing the image resolution [1]
changing the file formats of each of the individual images [1]
saving as a PDF [1]
or compressing /zip the folder with all the photos to a smaller size [1]