If more space is needed, temporary files will be used. Enable debug printout. More -v 's give more output. Also, version information is printed at startup. Same as -verbose .
Several options are available that trade off image quality to gain speed.
If this environment variable is set, its value is the default memory limit. The value is specified as described for the -maxmemory switch. To avoid the Unisys LZW patent, djpeg produces uncompressed GIF files. These are larger than they should be, but are readable by standard GIF decoders. Still not as fast as we'd like.