The internal structure of the files isn't changed. Only the compressed data is modified.
| -z, --recompress FILES... |
| Recompress the specified files. If the -1, -2, -3, -4 options are specified it's used the smallest file choice from the previous compressed data and the new compression. If the -0 option is specified the file is always rewritten without any compression. |
| -0, --shrink-store |
| Disable the compression. The file is only stored and not compressed. The file is always rewritten also if it's bigger. |
| -1, --shrink-fast |
| Set the compression level to "fast". |
| -2, --shrink-normal |
| Set the compression level to "normal". This is the default level of compression. |
| -3, --shrink-extra |
| Set the compression level to "extra". |
| -4, --shrink-insane |
| Set the compression level to "insane". It's VERY SLOW. |
| -f, --force |
| Force the use of the new file also if it's bigger. |