To reduce their size, images are compressed using Lempel–Ziv–Welch compression. Lempel-Ziv-Welch, or LZW, is a lossless compression. No information is lost when compressing or uncompressing. There were some problems with the patent of the LZW compression. That patent was not held by CompuServe, but by Unisys. These issues led to the development of another format, called PNG. This is no longer a problem, because the patents have expired.