File Compression | IGCSE Information and Communication Technology Preparation - Year 11 PDF Download

Why Reduce File Size?

• The file size impacts:
  • The amount of storage space needed.
  • The duration it takes to transmit from one device to another.
  • Compression is often employed to reduce file sizes.
• Two compression types are:
  • Lossy compression: Eliminates unnecessary data, notably shrinking file sizes. Typically used for audio, video, and images.
  • Lossless compression: Permits the original data to be perfectly reconstructed without any loss of information or quality. Commonly used for text, documents, and software.
• For instance, suppose 10 images, each originally 18MB, are to be displayed on a website with a 32 megabits per second internet connection. Loading the webpage would take approximately 45 seconds, requiring 180MB of online storage for the images. However, utilizing lossy compression could shrink the files to around 10% of their original size. With this compression, the same internet connection would only need 4 seconds to load the images, and the storage requirement would be reduced to 18MB.

How are Files Compressed?

Various technical methods exist for reducing file sizes, but some straightforward techniques for multimedia files are:

• Images compression:
  • Decreasing the number of colors in the image (bit depth).
  • Lowering the image resolution (total pixel count).
• Video compression:
  • Reducing the video resolution.
  • Decreasing the number of video frames per second.
• Sound compression:
  • Eliminating frequencies beyond the human hearing range.

How to Compress a File

• An uncompressed document containing both text and images
  
• A document can be compressed by converting it to a PDF file
  
• By converting the document to a pdf, the file size reduction is more than half
  

Compressing Multiple Images Together

• Hold Ctrl and select all the images you would like to compress, right click and choose ‘Compress to Zip file’
  
• Using the Zip file compression technique has reduced the file size considerably
  • Total for all files before compression: 8477KB
  • Total for all files after compression: 727KB

The same can be done using WinRar

• Hold Ctrl and select all the images you would like to compress, right click and choose ‘WinRAR followed by Add to Archive’
• Give the archive a title and click OK
• The compressed file is now in the directory

Note: At times, file sizes may not compress further when using WinZip or WinRar, particularly for file types like JPEG images, which are already compressed. Additionally, the effectiveness of compression algorithms can differ among compression software, influenced by the types of files being compressed.