As the depth and breadth of use of digital images increases and technology advances then new file formats are created to meet additional needs. There is a third type of file formats called Metafiles. These are a class of files that accommodates both vector and bitmap information - either both together or separately. Compression Bitmap files can become large very quickly. A linear doubling of image size results in a file 4 times larger.
Compression is one way of reducing file sizes.
An important property of this type of compression is that when the file is decompressed the image is restored to exactly as it was prior to compression. Compression ratios are not very high, typically about a 2 times reduction in files size. The degree of image degradation depends on the image content and the amount of compression applied. Clearly compressed image file formats should not be used as an archival format but can be used to deliver small representations of images when browsing an archive online.