/ 
Image-Synchronize-2.001
River stage zero No dependents
/ imsync

NAME

imsync - Synchronize image files' file system modification timestamps

SYNOPSIS

# report but don't modify
imsync
imsync --cameraid IMG_1234.JPG=MyCamera    # camera ID adjustment
imsync --time IMG_1234.JPG=+10m6s          # camera offset adjustment
imsync --time IMG_1234.JPG=14:22:46        # time adjustment
imsync --location IMG_1234.JPG=52.54,-11.7 # location adjustment

# modify as needed, and report
imsync --modify

# get help
imsync --help
imsync --man

SUMMARY

imsync [options] [path_patterns]

This application can synchronize filesystem modification times of images and movies created by one or more cameras, based on information embedded in the files and on adjustments provided by the user. It can also synchronize times of related files based on information from the image files that they are related to and on information provided by the user. Additionally, it can geotag images and movies, based on information extracted from GPX files.

Start by calling it without any arguments in the directory holding the images of interest. By default it reports what its inspection of the files yielded but does not modify any files (except for writing to log file imsync.log).

OPTIONS

--cameraid FILE=ID  Specify the camera ID for a file.  Can also be
                 written as --camera-id.
--clearlog       Clear the progress log before writing to it.
--exportgpx [FILE]  Export image geographical locations to this file.
                 If no file is specified, then uses export.gpx.
                 Can also be written as --export-gpx.
--fastscan N     Sets the speed of information extraction from
                 files, from 0 through 2.  Higher numbers mean
                 faster processing, but may miss some relevant
                 information.  Defaults to 1.  Is passed on to the
                 Image::ExifTool backend.  Can also be written as
                 --fast-scan.
--follow FILE    Be as verbose as possible for the indicated file.
--force          Inject missing tags also when modification time is
                 already correct.
--help, -?       Briefly explains how to use this application.
                 See also --man.
--location TGT=LOC  Copy the GPS location LOC to target TGT.
--logfile FILE   File to log to.  Can also be written as --log-file.
--man            Like --help but with more information.
--modify         Modify files as needed.  The opposite (and default)
                 is --no-modify, which reports but does not modify.
--norecurse      Do not process subdirectories.  The opposite (and
                 default) is to recursively process subdirectories,
                 too.  Can also be written as --no-recurse.
--offsetspath FILE  File to read camera timezone offsets from and
                 write updated ones to.  Defaults to
                 .imsync-cameraoffsets.yaml in the current or home
                 directories.  Can be written as --offsets-path.
--recurse        Process subdirectories, too.  This is the default.
                 Use --no-recurse to not process subdirectories.
--relativefiletime  Set file modification timestamps to the same
                 local clock times as in the (far-away) time zone
                 where the images were recorded, instead of setting
                 file modification timestamps to the same absolute
                 times.
--removebackups  Remove backup files.  Can also be written
                 as --remove-backups.
--removeourtags  Remove embedded tags that were added by this
                 application.  Can be written as --remove-our-tags.
--reportlevel N  Sets the level of detail of the final report.
                 Can also be written as --report-level.
--restoreoriginals  Restore original files from backups.  Can also
                 be written as --restore-originals.
--summertime FILE  The FILE's camera switched from Standard to
                 Daylight Savings Time just before that FILE.
--time FILE=TIME  Specify the target time or offset for a file.
                 Can be specified multiple times.
--unsafe         Don't create backup files, and delete the log file.
--verbose N      Sets the verbosity level, which is a combination of
                 bitflags (up to 31).
--wintertime FILE  The FILE's camera switched from Daylight Savings
                 to Standard Time just before that FILE.
--working-directory DIR  Changes to the specified working directory
                 first.

Option names can be abbreviated as long as they remain unique. For example, --reportlevel can be abbreviated all the way down to --rep, because no other option begins with that prefix.

ARGUMENTS

The arguments are zero or more path name patterns that identify files and directories to process. Wildcard * matches any number of characters, and wildcard ? matches a single character. If no arguments are specified, then the current directory is processed.

OPTION DETAILS

Some options involve a value that identifies files. The following methods to identify files are supported, but not all options support all methods.

  • by partial path name.

    A file matches if the file's path name ends with the given text.

  • by timestamp.

    A file matches if the file's embedded creation timestamp (tag CreateDate) corresponds to the given timestamp.

    The timestamp must include a date and a time, and may include a time zone offset designation. Here are two examples (in ISO 8601 format) that indicate the same instant of time:

    2015-09-17T22:14:33+01:00
2015-09-17T21:14:33Z

    Here are some other legal timestamps:

    2015:09:17 22:14:33+01             (same as previous)
2015:09:17 22:14:33                (Exif timestamp format)
2015-09-17T13:44
2015-09-17T13
2015:09:17T13:03

    The date and time must be separated by a capital T or by a single whitespace character. If you use the whitespace character, then enclose the entire option in double quotes, otherwise the whitespace is interpreted as a separator between different argument values.

    The date must include 3 numbers (year, month, day), all separated by a dash - or all by a colon :.

    The time is specified on a 24-hour clock and must include at least one and up to three numbers (hour, minute, second), separated by a colon :. Omitted final components are assumed equal to 0.

    The time zone offset designation, if specified, must follow the date/time specification without any intervening other text or whitespace. It consists of only the capital letter Z, or else of a plus +, minus − (Unicode character U+2212, may be displayed badly if your viewing application is not configured to display UTF-8), or dash -, followed by at least one and up to three numbers (hour, minute, second), separated by a colon :. Omitted final components are assumed equal to 0. The Z indicates a timezone offset equal to 0, i.e., UTC.

    If no time zone offset is specified, then the one according to the time zone rules of the current system is assumed.

  • by time range.

    A file matches if the file's creation timestamp is within the specified time range.

    The time range consists of two timestamps (as described above) separated by a solidus /. The second timestamp may omit the date, which is then assumed equal to that of the first timestamp. Likewise for the timezone offset. Here are some examples:

    2001-02-03T04:05:06+07:00/2009-10-11T12:13:14
2017-07-05T06/09:17:22

    The second example covers the period from 06:00:00 through 09:17:22 on July 5th, 2017, in the local timezone.

Which of these methods are supported is mentioned for each of the options.

Here begins a detailed description of all command-line options. In those descriptions, image file means a file containing a single image (picture) or multiple images (movie) and having an embedded creation timestamp.

--cameraid

--cameraid FILE=ID
--camera-id FILE=ID

Specifies the camera ID to associate with a target file FILE, if the camera ID that imsync proposed is not appropriate somehow.

FILE may be a partial path name, or a timestamp, or a time range, and identifies the files with which to associate the camera ID.

ID is the camera ID to associate with the files, instead of the default camera ID which depends on several embedded tags. Whitespace at the beginning or end of the ID is ignored, and the ID must not be empty.

If the file gets modified ("--modify"), then the specified camera ID is embedded in it (with our own XMP:CameraID tag).

--clearlog

--clearlog
--clear-log

Says to clear the previous contents of the progress log, if any, before writing the first message to it. If this option is not specified, then the previous contents of the progress log are retained and the new log messages are appended to it.

--exportgpx

--exportgpx
--exportgpx FILE

Also written --export-gpx.

Exports to the specified file (or export.gpx by default) the geographical position and time of all inspected files for which that information is available. Import the GPX file into a geographical application to see where the pictures were taken.

--fastscan

--fastscan N
--fast-scan N

Sets the speed of information extraction from files, from 0 through 2. Higher numbers mean faster processing, but may miss some relevant information. Defaults to 1. Corresponds to option FastScan in "Options" in Image::ExifTool.

--follow

--follow FILE

Make logging be as verbose as possible for the target FILE. FILE may be a partial file name, a timestamp, or a timestamp range. See also "--verbose".

--force

--force
--force --force

This application is reluctant to modify files. If no --force is applied, then a file is deemed to need modification only if one or more of the following are true:

  • the file's filesystem modification timestamp needs adjustment.

  • an explicit time ("--time") or location ("--location") is specified for the image file.

  • the file's GPS position needs adjustment, and the XMP:TimeSource tag is present and not equal to GPS (i.e., the existing GPS position was not embedded directly by a GPS receiver attached to the camera).

Use --force to override that reluctance, or --force --force for even more force.

With a single --force, the file is updated even if only tags within the following group need adjustment: XMP:CameraID, DateTimeOriginal, XMP:DateTimeOriginal, XMP:ImsyncVersion, XMP:TimeSource.

With two --force, the GPS position is updated even if the XMP:TimeSource tag is not present or is equal to GPS. This means the original GPS position that was embedded by a GPS receiver attached to the camera is lost.

If the only thing that has changed is the version of imsync, then the corresponding change to XMP:ImsyncVersion is suppressed. In other words, if XMP:ImsyncVersion is the only tag that needs a change, and if that tag was already in the file, then that change is suppressed.

--help

--help
-?

Prints a message briefly explaining the options and arguments of this program, then exits. See also "--man".

--location

--location TGT=LOC

Copies the location information indicated by LOC to target TGT, if the location (if any) proposed by imsync is not appropriate somehow.

The target may be identified by a partial file name, a timestamp, or a timestamp range.

The location may be identified by a partial file name, a location specification, or an empty value. If it is a partial file name then it must match only a single file, and then that file's location is copied to the target.

If it is an empty value then the existing location (if any) is slated for removal.

The location specification consists of the latitude and longitude in (optionally signed) decimal degrees, and optionally the altitude in meters above sea level, separated by commas. North latitudes, East longitudes, and altitudes above sea level may be prefixed by a plus sign +; South latitudes, West longitudes, and altitudes below sea level must be prefixed by a dash -.

--logfile

--logfile FILE
--log-file FILE

Specifies the file to write the log messages to (in addition to printing them to standard output). If not set, then imsync.log is used.

--man

--man

Like --help, but provides much more information about the application.

--modify

--modify

Modify files as needed. If not set, or if its opposite --no-modify (or --nomodify) is specified, then the indicated file changes are reported but the files aren't modified.

--norecurse

--norecurse
--no-recurse

Says to process the files in the specified directories (if any) but not those in any subdirectories of those specified directories. The opposite (and default) is --recurse, which says to recursively process subdirectories, too.

--offsetspath

--offsetspath FILE
--offsets-path FILE

Specifies the file for camera timezone offsets. Such offsets are read from the file when the application begins, and updated ones are written to the file (if --modify is specified).

Defaults to .imsync-cameraoffsets.yaml in the current working directory. If no such file exists, and if the HOME environment variable is set, then uses a file by the same name in the directory read from the HOME environment variable.

--recurse

--recurse

Process subdirectories, too. This is the default. The opposite is --norecurse.

--relativefiletime

Says to transfer the local time of the images (relative to the time zone where each image was taken) into the time zone of the current system. This makes images that were recorded near noon local time in different time zones show up near noon local time in the current system's time zone (when sorted by file modification time).

--removebackups

--removebackups
--remove-backups

This application only modifies a file if a backup of it exists. The backup has the same name, with _original appended to it. This option requests deletion of the backup files indicated by the arguments. The application then does nothing else.

If you want to remove all backup files in or below a folder, then specify that folder. If you want to remove a particular backup file, then specify a pattern that matches its name, including the _original suffix. See also "--restoreoriginals".

--removeourtags

--removeourtags
--remove-our-tags

Remove the embedded tags that were added by previous runs of this application.

The following tags are only removed if XMP:TimeSource is set and has a value other than GPS: GPSLongitude, GPSLatitude, GPSAltitude, GPSDateTime, GPSDateStamp, GPSTimeStamp.

The following tags are always removed: XMP:CameraID, XMP:ImsyncVersion, XMP:TimeSource.

The XMP:DateTimeOriginal and DateTimeOriginal tags are not removed, because we cannot be sure that they were created by a previous run of this application.

--reportlevel

--reportlevel LEVEL
--report-level LEVEL

Sets the detail level for the final report:

0 suppresses the final report.

1 reports only about files for which a change is indicated.

2 reports all files (that weren't skipped), even those for which no change is indicated.

3 is like 2, but also display all camera timezone offsets.

--restoreoriginals

--restoreoriginals
--restore-originals

Restores original files from backup files.

If you want to restore from all backup files in or below a folder, then specify that folder. If you want to restore from a particular backup file, then specify a pattern that matches that backup file's name, including the _original suffix. See also "--deleteoriginals".

--summertime

--summertime FILE

This specifies that the clock of the camera that recorded the FILE was shifted forward by one hour (just) before that file was recorded. Use this when the camera clock switches from Standard Time to Daylight Savings Time.

FILE may be a partial path name, or a timestamp, or a time range. If it is a time range that matches multiple files, then the effect is as if only the first file matched.

The opposite is "--wintertime".

--time

--time FILE=TIME

Specifies the target time or time offset or camera timezone offset for one or more target files, if the time proposed by imsync is not appropriate somehow.

FILE may be a partial path name, or a timestamp, or a time range.

TIME may be a timestamp or a time only or an offset or a partial path name.

If TIME is a time only, then it must be a clock time with hours, minutes, and optionally seconds, separated by colons, similar to

17:22
17:22:43

This clock time is combined with a date such that the combined timestamp is at most 12 hours before or after the target file's embedded CreateDate -- so this only works if the target file has an embedded CreateDate. This is convenient if you wish to specify a precise target timestamp close to the CreateDate.

If TIME is an offset then it must be either an optionally signed number or else be similar to

+2y50d2h16m5s

where the number before y is the number of years (of 365 days), and likewise d for days, h for hours, m for minutes, and s for seconds. All of these components and the sign are optional, but any that do appear must appear in the given order. Here are some other examples:

3d10s             (for plus 3 days and 10 seconds)
-10d              (for minus 10 days)

The specified offset is interpreted relative to the embedded creation time of the file (tag CreateDate), so this only works if the file has that embedded tag.

If TIME is a partial path name, and if there is only a single file among the processed ones that matches that partial path name, then the initial DateTimeOriginal (from before imsync ran) of that single file is the target time for the target files.

--unsafe

--unsafe

Says to not create backup files before modifying original files. If modifying the original files fails, then there are no backup files to restore the original files from. If the program reaches its natural end, then the log file is deleted.

--verbose

--verbose LEVEL

Sets the verbosity level. It defaults to 0. Higher levels (up to 31) yield more verbose progress reporting.

--version

--version

Prints a message identifying the versions of this application, GetOpt::Long, and Perl.

--wintertime

--wintertime FILE

This specifies that the clock of the camera that recorded the file was shifted backward by one hour (just) before that file was recorded. Use this when the camera clock switched from Daylight Savings Time to Standard Time.

FILE may be a partial path name, or a timestamp, or a time range. If it is a time range that matches multiple images, then the effect is as if only the first image matched.

The opposite is "--summertime".

--workingdirectory

--working-directory DIR
--workingdirectory DIR

Change the working directory to DIR before starting processing.

DESCRIPTION

This application can synchronize filesystem modification times of images and movies created by one or more cameras, and times of related files, based on information provided by the user and on information embedded in other processed images by the same cameras. Additionally, it can geotag images and movies, based on information extracted from GPX files.

Information embedded in image and movie files is extracted, modified, or added using Image::ExifTool, so if that module cannot access tags embedded in some file, then neither can this application. Names of embedded tags that are mentioned below are as recognized by that module.

Several passes are made over all relevant files:

1. Inspect

During the first pass, all selected files are inspected for relevant information, but are not modified, because we may be able to use information from a later image to synchronize the time of an earlier image, but we can't tell until we've inspected all files.

Relevant properties are noted, and files that provide too little information are omitted from further consideration.

2. GPX

During the second pass, GPS times and locations are extracted from all detected GPX files.

3. Determine

During the third pass, the target time and (if possible) location is determined for all remaining files. The time and location are based on information found during the first two passes.

The target timestamp for each file is based on information in that file and (where useful) in other files recorded by a camera with the same camera ID, or in other files with the same file number.

4. Modify

If file modification is requested ("--modify"), then during the fourth pass the files are adjusted as needed to give them their target time and location.

Progress for each pass is shown in a progress bar (if the application is run interactively). The progress bar advances whenever another file has been processed, so if processing a file takes a long time, then the progress bar may appear to be stuck. Progress messages are logged, with configurable verbosity ("--verbose"). In the end, a configurable report is displayed ("--report-level"), indicating the target time and other information of interest for relevant files.

Camera ID

Images from multiple cameras may be processed in a single run. The cameras' internal clocks may each show a different time because they haven't been set correctly or because they slowly drift away from the correct time or because they've been configured for different time zones, so a time zone offset detected for one camera is no good for another camera. We must associate offsets with specific cameras, which means we must identify the camera.

Most cameras embed the camera's make and model (tags Make and Model) in the images. Some also embed a camera serial number (tag SerialNumber) in the image files. If these properties aren't all absent or empty, then their combined values, separated by pipe symbols |, constitute the (preferred) camera ID. Camera timezones are registered for each camera ID separately.

If none of the make, model, and serial number are embedded in an image file, then the fallback camera ID may be used. The fallback camera ID is derived from the file name by (1) omitting the directory part, (2) omitting the file name extension, (3) replacing any sequence of digits by the length of that sequence, and (4) prefixing a question mark ?. For example, the fallback camera ID of file vacationpics/IMG220_5532.JPG is ?IMG3_4.

If a file has no make/model/serial number from which to produce a preferred camera ID, then it may get the preferred camera ID of other image files for which the fallback camera ID is the same as the fallback camera ID of the file, if there is only a single preferred camera ID associated with that fallback camera ID during the current run.

Multiple cameras may end up associated with the same camera ID if the camera identifying information isn't unique, for example if two cameras have the same brand and type and do not include a serial number in the images. In that case, a distinct camera ID may be assigned to the images manually, using the "--camera-id" command-line option.

The camera ID is embedded in the images (our own tag XMP:CameraID) if the images are modified ("--modify"), so that you don't need to specify it again if the image is processed again using this application later.

Camera Timezone

We need to know the difference between the times reported by the cameras' clocks (which produced the timestamps embedded in the images) and Coordinated Universal Time (UTC), so that we can synchronize image times between different cameras and we can assign locations based on GPS tracks. The cameras' clocks may each show a different time because of time zone differences and clock drift. Many (especially older) image files contain no embedded timezone information at all.

The camera timezone offset is the difference between the time zone of the camera's clock (including any clock drift) and UTC. If the embedded timestamp says 17:24:33 and the corresponding UTC time is 15:23:11, then the camera timezone is +02:01:22.

The camera timezone information is valuable: If one has been found for one image, then it can be applied to other images from the same camera as well.

If the first image processed for a particular camera ID has no timezone information in its embedded timestamps, then its embedded timestamps are assumed to have been recorded in the local timezone that was appropriate for that date and time on the system where the current application is running. When other images for the same camera ID are processed later, then at least one camera timezone offset is already known for that camera ID and can be reused.

Use "--time" to set a different target time for an image if needed. This defines a camera offset for the associated camera, which can be used to deduce a target time for other images taken by the same camera. You need to specify only a single "--time" for a given camera, until the associated camera offset is no longer correct (e.g., because of clock drift).

Camera Timezone Offsets File

At the start of the run, camera timezone offset information is read from the camera timezone offsets file. The additional camera timezone information that is gathered during the run is merged into the preloaded information and gets written to the same file again (if "--modify" is specified). If the "--offsets-path" command-line option is specified, then its value identifies the camera timezone offsets file. Otherwise, if there is a file called .imsync-cameraoffsets.yaml in the current working directory, then that is the file to use. And if that file doesn't exist, then the same file in the user's home directory (as determined by the HOME environment variable) is used.

The information is written to the file in YAML format. It consists of a single map of which the keys are the camera IDs. The corresponding values are maps, of which the keys are timestamps in the camera's timezone and the values are camera timezone offsets that are valid from the time indicated by the key. Here is an example:

---
CameraID1:
  2017-06-22T15:57:01: +0:00
CameraID2:
  2017-06-19T14:08:22: +0:05:46+03:00
CameraID3:
  2017-06-20T00:15:54: +4:00
  2017-06-23T05:21:25: +2:00
  2017-06-25T13:44:12: +0:00+02:00

From the cameras with camera IDs CameraID1 and CameraID2, only a single image or movie each has been processed so far. The camera with camera ID CameraID3 has produced multiple image files, of which the ones from the first until just before the second timestamp were taken when the camera clock corresponded to UTC+4:00, and the ones from the second through the last timestamps were taken when the camera clock corresponded to UTC+2:00.

Since version 2.001 of this application, camera timezone offsets get stored with two time components, for example +0:00:15+02:00. The second component specifies the time zone that is appropriate for the images (the "nomimal timezone" that was in effect in the location where the image was recorded), and the first component specifies the clock drift relative to that time zone. In the example, the image was taken in a location where the timezone UTC+02:00 was active, and the camera clock was 15 seconds ahead of the clock time in that timezone.

Older versions of this application stored camera timezone offsets consisting of a single value. The sum of the two newer values corresponds to the older value.

Specifying the offsets as two values is relevant for the "--relativefiletime" option.

For each camera ID, the first and last included timestamps are associated with the oldest and youngest image files recorded by that camera and processed by the current application.

Image Files with Embedded Timestamps in UTC

The embedded timestamps in most image files show the camera clock time, which is usually in or near the local timezone. However, some image files (such as Apple QuickTime files) have embedded timestamps that are supposed to be in the UTC timezone, regardless of the local timezone. They aren't always, because many cameras don't know what timezone they're in and so don't know what the time in UTC is. In any case, timestamps embedded in supposedly-UTC image files may be relative to a different timezone than timestamps embedded in other image files recorded by the same camera.

This means that it is convenient to treat supposedly-UTC image files as if they are recorded by a different camera than the local-timezone image files taken by that camera, otherwise the camera timezone offset keeps switching to and fro between the local timezone and UTC when both types of image files from the same camera are mixed.

To this end, supposedly-UTC image files get an extra |U appended to their automatically determined camera ID. If the camera ID for a local-timezone image file is Brand|Model|SerialNumber, then the camera ID for a supposedly-UTC image file by that same camera is Brand|Model|SerialNumber|U.

At present, only Apple QuickTime movies fall into this category. Use the "--cameraid" option to assign different camera IDs when needed.

GPS Fix Lag

An image recording device such as a smartphone that incorporates a GPS receiver can embed a GPS time and location into an image file when that file is created. That GPS location/time is the one obtained most recently, which may already be a few seconds old when the image is recorded. I call the difference between the time of the GPS fix and the time at which the image was recorded the GPS fix lag. If the GPS timestamp is used as is to calculate the camera timezone offset, then that timezone offset will be off by a few seconds because of the GPS fix lag, and the error may vary from one image to the next.

Fortunately, devices incorporating a GPS receiver know the time very accurately, so the difference between their true camera timezone offset and UTC should be an exact multiple of 15 minutes, because all official time zones in use around the world are like that.

If the image has an embedded GPS timestamp already, and that timestamp is not marked as having been added by an earlier run of the current application (see "TimeSource"), and the deduced camera timezone offset differs less than 2 minutes from a multiple of 15 minutes, then that multiple of 15 minutes is used as the camera timezone offset instead.

For example, if an image has the following embedded timestamps

GPSDateTime = 2015-03-17T14:15:16
CreateDate  = 2015-03-17T11:15:23

then the nearest multiple-of-15-minutes timezone offset is -3:00:00 and the GPS fix lag is 7 seconds.

Custom Times

If the absolute target time proposed for an image file by the current application is incorrect, then there are several ways to adjust it.

  • Use the "--time" command-line option to specify the desired target time, or the amount by which to correct the proposed target time, or another file from which to copy the timestamp.

  • Use the "--summertime" or "--wintertime" command-line options to adjust the proposed target time by exactly one hour.

  • Manually adjust the camera timezone offsets file ("Camera Timezone Offsets File").

TimeSource

The current application can tell from the XMP:TimeSource tag what the source of the embedded location information and GPSDateTime (if any) is, because the current application adds such a tag when it modifies an image file. The tag gets one of the following values:

GPS

There was already a GPSDateTime (and presumably a location) in the image file when the current application first processed that file. The current application does not change the target timestamp or location, except perhaps if "--time" or --force --force is specified for that file.

User

The user provided the target timestamp through the "--time" command-line option. The current application does not change the target timestamp (unless another --time is specified for the same file), but can change the location if a different GPX file is provided.

Other

The target timestamp was based on a camera timezone offset. The current application may change both the target timestamp and the location.

If there is a GPSDateTime but no XMP:TimeSource, then the file is treated as if XMP:TimeSource is GPS.

Target Timestamps

The target timestamp is the timestamp that is going to be assigned to the file.

If a time is specified for the file through the "--time" command-line option, then that time is used as the file's target time.

Otherwise, if a camera timezone offset is specified for the file through the --time command-line option, and if the file contains an emedded creation timestamp (tag CreateDate), then the target time is the creation timestamp relative to the timezone indicated by the camera timezone offset.

Otherwise, if the file contains a GPS timestamp (tag GPSDateTime), then its target time is based on that (but see "GPS Fix Lag").

Otherwise, if camera timezone offsets are already known for that camera's camera id, then the relevant camera timezone offset is applied to the file's embedded creation timestamp to find the target time.

Otherwise, if the file has an embedded original timestamp (tag DateTimeOriginal), then it is used as the target time.

Otherwise, if the file has an embedded creation timestamp (tag CreateDate), then it is used as the target time.

Otherwise, the file is considered not to be a regular image file, and is marked for later processing after all regular image files have been processed. See "File Numbers".

Relative File Times

By default, target timestamps are absolute times. If two people take pictures of the same event (such as of a lunar eclipse, or of themselves calling each other) and then properly use the current application, then their images end up with nearly the same timestamp when measured relative to UTC, even if those images were recorded in locations in very different time zones. However, absolute timestamps are not always the most convenient for organizing and displaying your images and movies.

Suppose that you travel to a location in a very different time zone. The daytime in that location is shifted by some hours relative to the daytime of your home location. You go to dinner at the local dinner time, sleep during the local night, and take sunny pictures during the local daytime. When you get back home and use the current application to synchronize your images, then they end up at the correct absolute instants of time, but the daily rhythm visible in those pictures is shifted some hours relative to the clock time of your home location. That picture of your dinner may end up with a file modification timestamp after midnight in your home time zone, and those sunny pictures may end up after dark in your home time zone. If your image viewing application displays the file modification timestamps, then they won't show what clock time it was over there, but rather what clock time it was back home at that same instant.

If "--relativefiletime" is specified, then the target timestamp gets adjusted for the difference between the remote and local time zones, such that pictures taken near noon at the remote location get file modification timestamps near noon on the current system.

Only the file modification timestamp gets adjusted in that way. The timestamp (if any) that gets embedded in the image (tag DateTimeOriginal, and GPSDateTime if available) still represents absolute time.

File Numbers

If the name of a file (excluding any directory part and excluding the file name extension) contains any digits, then the last consecutive sequence of digits defines the file number. For example, if the file name is DSC1234.JPG, then the file number is 1234. If the file name is Q5422_5376.TXT, then the file number is 5376. If a target timestamp cannot be found for a file using the method outlined above, then a target timestamp can be copied for it from another file with the same file number. In this way, non-image files end up near the corresponding image files in the same directory, when sorted by their file system modification timestamp.

If there is more than one file with the same file number and with a target timestamp, then the one "closest" to the current file in the file system is chosen to donate its target timestamp.

Locations

The current application can set or modify location information embedded in an image file.

If the location information already embedded in an image file wasn't put there by the current application (tag XMP:TimeSource is absent or has value GPS), then the current application doesn't change it, except perhaps if --force --force is specified. In most cases that information will have been produced by a GPS receiver incorporated into the image recording device, so it is hardly possible to improve that location information.

GPX files can contain location information for multiple time intervals. If a GPX file is processed together with some image files, and if the target time of one of the image files is within the time period covered by one of the tracks from a GPX file, then the current application calculates a location for the target time and associates that with the image file.

If there are multiple GPX tracks that cover the target time, then the track from the GPX file closest (in the file system) to the image file is used.

If there are no suitable GPX tracks, then a location can be manually specified for an image file using the "--location" command line option.

Modification

Each file's relevant properties deduced during the 'Determine' phase are compared with the original values deduced during the 'Inspect' phase. If some of the properties have changed, then modification of the file may be indicated.

If "--force" is not specified, then modification is indicated if the deduced file modification timestamp differs from the original one.

Modification is then also indicated if the GPS position has changed, but only if the original GPS position was provided by the current application (as shown by the XMP:TimeSource tag being set and unequal to GPS). We refer to such a GPS position as flexible. We do not want to lightly lose the GPS position embedded in the file by the original camera.

If --force is specified, then modification is also indicated if any of XMP:CameraID, DateTimeOriginal, XMP:ImsyncVersion, or XMP:TimeSource differ from the original ones.

If --force --force is specified, then modification is also indicated if the GPS position has changed by at least 1 meter and is not flexible.

If modification is indicated, then the file only gets modified if "--modify" is specified. Without that option, the proposed modifications are reported but not applied.

If the file does get modified, then all of the changed tags are updated (as far as the target file type supports the tags), but the GPS position only if it is flexible or if "--force --force" is specified. If the file gets modified and already had a GPS position but no XMP:TimeSource yet, then it gets an XMP:TimeSource equal to GPS. If the GPS position is new and was specified through "--location", then XMP:TimeSource gets the value User. If the GPS location was obtained from a GPX file, then the tag gets the value Other.

Backups

If a file (other than the log file and the camera offsets file) is going to be modified, then imsync creates a backup of it first, if no backup already exists. The backup has the same name but with _original appended to it. If the backup cannot be created then the original file is not modified.

Additionally, the Image::ExifTool module that imsync uses to write the image tags creates a temporary backup file before modifying any tags, and deletes that backup file if no problems were detected, but the author of that module recommends backing up your files anyway.

If you're satisfied that the modification was a success, then you can delete the backup that imsync created, either manually or using the "--removebackups" option. Use the "--restoreoriginals" option to restore original files from backups.

If you want to skip creation of backup files by imsync, and rely on the temporary backups created by Image::ExifTool, then use the "--unsafe" option.

Logging

Progress messages are printed to the standard output stream and are appended to a log file. The default log file is imsync.log in the current working directory, but a different file can be specified using the "--logfile" command-line option.

If the log file already exists at the beginning of the run, then use the "--clearlog" command-line option if you want its previous contents to be removed. Otherwise the progress messages from the current run are appended to the existing contents.

If the "--unsafe" option is used, then the log is deleted if the application reaches its natural end. If there is a serious problem that prevents the application from completing its task, then the log remains.

Verbosity

The "--verbose" and "--follow" command-line options determine how verbose the logging is, except for the final report which is governed by "--reportlevel" insead.

With no --verbose, or with --verbose 1, summary information is printed.

To print original details of all inspected files, add 2.

To print details of the determination of final values only for files for which a change is indicated, add 4.

To print details of the determination of final values for all files, add 8.

To print all imported camera offsets, add 16.

If you want to see the most verbose information but only for particular files, then use the --follow command-line option to identify the files of interest. Progress messages for those files are printed as if the verbosity level is infinitely large, regardless of the verbosity level set through --verbose.

Report

By default, the files that require a modification are listed in the report. If you want to report on all files, then specify "--reportlevel 2". If you want no report at all, then specify --reportlevel 0.

The report looks something like this:

GEOMPF Cm Target Time               M Offset   c Offset File
------|--|-------------------------|----------|--------|--------
-=-*-0 SO 2017-06-22T00:33:02+02:00 s  -29d7h.        0 DSC03741.JPG
-*+*-0 AP 2017-06-22T14:23:35+02:00 s -28d17h.      +2h IMG_0095.JPG

The GEOMPF field shows what happens if --modify is specified, to, respectively, (G) the embedded GPS timestamp (tag GPSDateTime), (E) the embedded original timestamp (tag DateTimeOriginal), (O) various embedded tags not covered by the other categories, (M) the file system modification time, and (P) the embedded GPS position (tags GPSLatitude, GPSLongitude, and possibly GPSAltitude). The F column shows what level of "--force" is needed to modify the file (0 means no --force, 1 means --force, and 2 means --force --force). In the other columns, a - means the tag remains absent. A = means the tag exists and its value remains unchanged. A * means the tag's value is modified. A + means the tag is added, A ! means the tag is removed.

The Cm field identifies the camera ID with an abbreviation that is explained in a table printed before the report.

The target time field shows, well, the target time, in ISO8601 format including the timezone, if known.

The M Offset field shows what time offset is added to the file system modification timestamp, in units of years (y), days (d), hours (h), minutes (m), and seconds (s). If the value had to be truncated to fit in the available space, then it ends in a period (.). For example, -37d2h means exactly -37 days and 2 hours, and -37d2h. means the value was truncated from an amount slightly larger than that.

The letter at the beginning of the M Offset field says what the source of the target time was, according to a table printed before the report.

The c Offset field shows the difference between the target time and the embedded creation time of the image, formatted similarly to the offset in the M Offset field. For example, +2h means the target time is exactly 2 hours later than the embedded creation time.

The File field identifies the file, including just as much of the directory part of the name as is needed to make the file name unique within the collection of files that were processed.

Export GPX

The location information from (or for) the processed files can be exported to a GPX file, even if file modification ("--modify") is not requested. In this way you can verify the positions in a mapping tool and only embed the locations in the image files when you're satisfied they are correct. Use the "--exportgpx" option to request export of location information to a file. If you specify a file name after the option, then the information is exported to the named file. Otherwise, the information is exported to file export.gpx in the current working directory.

EXIT STATUS

The current application returns 0 if it detects nothing left to change for the inspected image files, 1 if it identified additional changes to make for one or more image files, and 2 if there was a severe problem that prevented it from completing.

CONFIGURATION

The current application reads and writes a "Camera Timezone Offsets File" that contains information (in YAML format) about how the camera clocks run compared to Coordinated Universal Time (UTC). If there is a file .imsync-cameraoffsets.yaml in the current working directory, then it is used as the camera timezone offsets file. Otherwise, a file by that same name in the user's home directory (as determined by the HOME environment variable) is used.

DEPENDENCIES

This application uses the following non-core Perl modules:

AUTHOR

Louis Strous <LS@quae.nl>.

LICENSE AND COPYRIGHT

Copyright (c) 2018-2020 Louis Strous.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.