Full color images (illustrations, photographs, or scans), require a considerable amount of memory to store as an uncompressed digital file. In order to reduce the file size, an image file can be saved in a variety of formats which allows it to be compressed. Each file format compresses the file differently, resulting in varying degrees of file size. The most common image formats are JPEG, and TIFF.
The JPEG file format uses a file compression that permanently removes information from the image it deems as “unneccessary”. This is known as a lossy file format. As a result of information being removed, a JPEG file will require a smaller amount of memory to store the file. The JPEG format is the most popular type of image file.
The TIFF file format uses a compression which results in no loss of information in the image. This is what is referred to an a lossless file format. Instead, information is reorganized and condensed in a more efficient way, resulting in a reduction in the file size.
For example, a printed image is made up of fine dots of varying colors. If an image contains 400 dots using the same blue color, an uncompressed file stores the information as “blue dot, blue dot, blue dot”, and so on (400 times in total). When the file is compressed, the information is stored simply as “blue dot x 400”. This is why images containing large areas of the same color will result in yet a smaller file size.