Compression

The Need for Compression

Compression is used to reduce the size of files, making them easier to store and transfer.
Large files, such as images, videos, and software, can take up significant storage and require a long time to upload/download.
Compression is necessary to improve transfer speed, save storage space, and make file sharing more efficient.

Lossy compression permanently removes some data from the file to reduce its size.
It is commonly used for media files like images, audio, and video (e.g., JPEG, MP3, MP4).

Advantages:

Significantly reduces file size, making it ideal for online streaming and storage. Disadvantages:
Some data and quality are lost, meaning the original cannot be perfectly restored.
Quality reduction may be noticeable, such as in blurry images or reduced audio clarity.

Effect on file: The file becomes much smaller, but the quality decreases depending on the compression level.

Lossless compression reduces file size without losing any data.
Used for files where it is essential to maintain original quality, such as text files, ZIP files, and some image formats (e.g., PNG).

Advantages:

No loss of data, so the file can be restored to its original state.
Ideal for compressing important documents and high-quality images. Disadvantages:
Less reduction in file size compared to lossy compression.

Effect on file: The file size is reduced, but quality is preserved.

Media files: Images, videos, and music are compressed to reduce file size and speed up sharing over the internet.
Documents: Text and data files (e.g., ZIP archives) are compressed using lossless compression to save space without losing information.
Websites: Images and files on websites are often compressed to help them load faster, improving the user's experience.

Bitmap images are made up of tiny squares called pixels. Each pixel stores a specific colour using a binary code.
The colour depth of an image refers to how many bits are used to store each pixel's colour. More bits = more possible colours:
- 1 bit can store 2 colours.
- 2 bits can store 4 colours.
- 3 bits can store 8 colours.
- 4 bits can store 16 colours.
Resolution refers to the number of pixels in an image. Higher resolution = more detail but a larger file size.

Pixel: The smallest unit of an image, representing one colour. Each pixel is stored as a binary value.
Colour Depth: The number of bits used to represent the colour of a pixel. More bits allow more colours but increase file size (e.g., 4 bits = 16 colours, 8 bits = 256 colours).
Resolution: The density of pixels in an image, usually measured in dots per inch (DPI). Higher DPI = more pixels, higher quality, and larger file size.
Metadata: Extra information stored with an image, such as its resolution, colour depth, file format, and camera settings (e.g., exposure, ISO, aperture).

Larger colour depth and higher resolution result in better image quality, but also larger file sizes.
Smaller colour depth and lower resolution create smaller file sizes, but the image quality decreases.

File size formula: Multiply the image's resolution by its colour depth (in bits).
To convert bits to bytes, divide by 8. For example, a 100x100 pixel image with 8-bit colour depth would have a size of:
- Size = 100 x 100 x 8 bits = 80,000 bits
- Divide by 8 to get 10,000 bytes (or 10 KB).

infoNote

Compression reduces file size to save storage and improve transfer speeds.
Lossy compression removes some data permanently, reducing quality but saving significant space (e.g., JPEG, MP3).
Lossless compression reduces size without losing data, preserving quality (e.g., ZIP, PNG).
Bitmap images use pixels, and their file size depends on colour depth (bits per pixel) and resolution (pixel density).
Higher colour depth and resolution improve quality but increase file size.