I'm making a minor change to a very large file image file (just a few pixels difference) which takes a long time to transfer over the network. Is there a way for rsync to identify the difference in the file and only send the small diff over the network?
Can rsync update a large file that has only changed partially without full retransmission?
rsync;diff
rsync delta-transfer algorithm does this by default. Quoting rsync manpage:DESCRIPTIONRsync is a fast and extraordinarily versatile file copying tool. It  can copy locally, to/from another host over any remote shell, or  to/from a remote rsync daemon. It offers a large number of options  that control every aspect of its behavior and permit very flexible  specification of the set of files to be copied. It is famous for its  delta-transfer algorithm, which reduces the amount of data sent over  the network by sending only the differences between the source files  and the existing files in the destination. Rsync is widely used for  backups and mirroring and as an improved copy command for everyday  use.If you want to disable it, you will have to use the -W or --whole-file option. -W, --whole-file This option disables rsync's delta-transfer algorithm, which causes all transferred files to be sent whole. The  transfer may be faster if this option is used when the bandwidth  between the source and destination machines is higher than the  bandwidth to disk (especially when the disk is actually a networked  filesystem). This is the default when both the source and destination  are specified as local paths, but only if no batch-writing option is  in effect.If you really know how much your file have changed doing, you could even optimize this delta transfer behavior by tunning your delta block size:-B, --block-size=BLOCKSIZEThis forces the block size used in rsync's delta-transfer algorithm to a fixed value. It is normally selected  based on the size of each file being updated. See the technical report  for details.And if you want more information about the algorithm itself, you can find it here: The Rsync algorithm