What is appropriate for display on a computer screen is not always the best quality for printing. If network access is a concern, determining which is likely to be the preferred viewing format may be important. Larger numbers of colours or grays increase the size of the image. Resolution is usually measured in a unit of picture elements called a pixel . The size of image files can be reduced by a variety of methods.
Compression is important in managing the size of image collections.
Methods which remove information from an image are called lossy compressions . Lossless compression of an image will provide an identical image when decompressed as existed before compression. Being digital does not mean being accessible. There are national and international standards for image-file formats and compression methods. These exist to ensure that data will be interchangeable among systems.