Since there has been some discussion about the validity of the private NKI compression (see topic Conquest and Ultrasound), here are my views.
NKI compression is an old and well tested feature of the Conquest DICOM server. We use it to store TB's of information. The compression ratio and speed are quite OK.
It is totally transparant for clients accessing conquest over the network, guaranteed error free, and safe to use.
Also (when set in acrnema.map) it can set as transfer syntax to transfer data from one server to another. This is OK for Conquest to Conquest transfers but should NEVER be done for transfers from Conquest to non-Conquest clients.
The compressed data is saved in a private TAG if possible. If not, the images are not compressed and remain valid.
Files stored by Conquest under NKI compression are NOT DICOM COMPLIANT and are unreadible for other software. Originally, it was not possible to store NKI compressed images with the .dcm extension (set with FileNameSyntax), but only with the .v2 extension (raw VR dump). That the combination of .dcm and NKI compression is now possible can actually be considered a bug - .dcm files must be DICOM compliant. Since version 1.4.12b, the nki compression is disabled for .dcm files.
If you store data with NKI compression, you will need to keep the a version of the Conquest software running indefinitively to be able to read the data (or reuse our code in nkiqrsop.cxx).
As David Clunie mentioned, a better way to implement NKI compression is a private transfer syntax. We will consider this change, but it has a lot of implications for the code.