Notes about the XJTGZ file extension:
Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The XJTGZ file type is primarily associated with 'Compressed GIMP Image with Properties of GIMP'. XJT uses JPEG compression for each layer or channel and TAR to collect all layers in one file. (Layers with alphachannels are split into 2 JPEG files). Additional property information about offsets, opacity, layer names etc. are stored in the readable textfile called "PRP" (Properties). The resulting tar-file is optionally compressed a 2nd time using GZIP or BZIP2 (filename ends in "gz" or "bz2" accordingly).