Despite Kodak not releasing the specifications for the Photo CD format, it has been reverse engineered, so allowing images to be converted to more modern formats. The original reverse engineering work was performed by Hadmut Danisch of the University of Karlsruhe, who deciphered the format by studying hex dumps of Photo CD files, and subsequently wrote hpcdtoppm, which converts Photo CD Images to PPM format, in the early 1990s. During the early 1990s, hpcdtoppm was extensively distributed as part of various Linux distributions, but has since been almost entirely abandoned due to concerns about hpcdtoppm's restrictive license conditions and lack of color management. However, Hadmut Danisch's reverse engineering work has been used to create a number of other open source implementations of Photo CD decoders such as ImageMagick. In 2009, pcdtojpeg was created under the GPL open source licence. Also acknowledged by the author to be based on Hadmut Danisch's reverse engineering work, pcdtojpeg allows Photo CD metadata to be decoded, is color managed, and can decode all known variants of Photo CD files. Currently hpcdtoppm and pcdtojpeg together form the core of information available in the public domain on the technical details of the Photo CD format.