EXIF File Creation Time Shifts w/ Time Zone Change

[William H. Magill]

On Jul 7, 2013, at 12:30 PM, iamabbqueen <captenaj@gmail.com> wrote: > > > Thanks to this discussion, I am understanding the different dates and times stored with an image much better. In looking at the EXIFTool by Phil Harvey data, the date/time items are: > > ---- System ---- > File Modification Date/Time: 2013:06:12 19:04:42-05:00 > File Access Date/Time: 2013:07:07 07:53:48-05:00 > File Inode Change Date/Time: 2013:07:06 21:06:28-05:00 > ---- IFD0 ---- > Modify Date: 2013:06:11 09:31:25 > ---- ExifIFD ---- > Date/Time Original: 2013:06:11 09:31:25 > Create Date: 2013:06:11 09:31:25 > ---- Sony ---- > Sony Date Time: 2013:06:11 09:30:54 > ---- GPS ---- > GPS Date Stamp: 2013:06:11 > ---- IFD1 ---- > Modify Date: 2013:06:11 09:30:54 > ---- XMP-exif ---- > Date/Time Digitized: 2013:06:11 09:31:25 > Date/Time Original: 2013:06:11 09:31:25 > GPS Date/Time: 2013:06:11 14:31:25 > ---- XMP-xmp ---- > Create Date: 2013:06:11 09:31:25 > > Those who know better, please correct me if I am wrong. > > When I took the above photo, the time was recorded to the photo dependent on the time set in the camera. This is "2013:06:11 09:30:54." I imported the photos through GC to my computer and shifted the EXIF timestamp (Action> Metadata> Shift EXIF Timestamp, with the "Set the file date identical to the EXIF date" box checked) so the time matched that on my GPS. I then used GPSPhotoLinker to tag each photo with GPS data. > > Somewhere in this process, there is a bit of information recorded indicating the timezone of the photo. The only place I see this information in the above data is in the 3 "---- System ----" dates but the times indicated do not match any of the other EXIF times. > > Next, when I change timezones and access the photo again, the system takes the EXIF time and shifts it into the current timezone. > > Another point: I read in the Apple forums that "The Finder doesn't work with EXIF." Also in the forums: "...the dates are not actually carried in the file headers as numbers. They are special "date" fields, which are the number of seconds since a certain date (different OSs use different starting points). Whenever they need to be displayed, they're converted to what us mere mortals recognize as a date, using the system time zone settings." Much of the date/time issue is an OS issue, not GC. All Unix based systems use the same "epoch time." (OSX is Unix based) --- open a terminal window and type: "man time" then "man date" for all you might want to know about OSX. All "accessories" -- like GPS units and Cameras are also "Unix based." (I.e. POSIX/ISO standards compliant) The concept of "time zones" does NOT appear anywhere in the standards. It is up to the individual "user" (in this case, the OS) to maintain any time-zone information independent of the time field. Note that "date" is also NOT maintained as pat of the time field... it too is a construct computed by the Operating System What is epoch time? The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of seconds that have elapsed since January 1, 1970 (midnight UTC/GMT), not counting leap seconds (in ISO 8601: 1970-01-01T00:00:00Z). Literally speaking the epoch is Unix time 0 (midnight 1/1/1970), but 'epoch' is often used as a synonym for 'Unix time'. Many Unix systems store epoch dates as a signed 32-bit integer, which might cause problems on January 19, 2038 (known as the Year 2038 problem or Y2038). Time Synchronization is another whole kettle of fish. OSX uses a protocol called NTP (Network Time Protocol) to set the date and time -- System Preferences/Date & Time. You can select "check date and time automatically" and define a "time server" -- the default is checked and Apple Americas selected. On the next panel "Time Zone" you can select -- "Set time zone automatically using current location" -- this is useful on a laptop that is "in transit" a lot -- but it also means that what you see for time zones "changes." A GPS may or may not use NTP to set and maintain its timestamp information. There is time information associated with basic GPS data as well as triangulation data from Cell Towers which is frequently used for GPS data. Again, the actual "timestamp" is stored in seconds since the Epoch. So, in short... a Timestamp -- is never seen by human eyes.... it's a 32bit signed integer. That is what the camera records, what the GPS records, what OSX records. What is DISPLAYED to you (the human) will change depending upon what filters you are applying to that 32bit signed integer. In the example above, the first 3 "time displays" include -0500 -- That might mean EDT... or it might mean CST - depending upon where you are and what the settings in your system are. None of the other displays contain that offset from GMT. Time on computers is both "relative" and "absolute," at the same time. It is a constant source of "fun" for us in the business. T.T.F.N. William H. Magill # iMac11,3 Core i7 [2.93GHz - 8 GB 1067MHz] OS X 10.8.4 # MacBook Pro4.1 Core 2 Duo [2.5GHz - 4GB 667] OS X 10.6.8 # Macmini6,1 Intel Core i5 [2.5 Ghz - 4GB 1600MHz] OS X 10.8.3 magill@icloud.com magill@mac.com whmagill@gmail.com

[Norm Siler]

Thank you, Mr. Maglii. For instructing many more of us in both the technical points and the terminology to do so. My single point of question is the adjustment you suggest for CST and EDT. Here at approximately 90 West longitude, in the Central Time zone, I am accustomed during Standard Time months to applying a -0600 adjustment. During Daylight Time months, as now, I apply -0500 to GMT, one quarter of the 24 time zone globe from Greenwich. In no way diminishing my appreciation for your thorough explanation. Norm Siler --- In gcmac@yahoogroups.com, "William H. Magill" <magill@...> wrote: > > > On Jul 7, 2013, at 12:30 PM, iamabbqueen <captenaj@...> wrote: > > > > > > > Thanks to this discussion, I am understanding the different dates and times stored with an image much better. In looking at the EXIFTool by Phil Harvey data, the date/time items are: > > > > ---- System ---- > > File Modification Date/Time: 2013:06:12 19:04:42-05:00 > > File Access Date/Time: 2013:07:07 07:53:48-05:00 > > File Inode Change Date/Time: 2013:07:06 21:06:28-05:00 > > ---- IFD0 ---- > > Modify Date: 2013:06:11 09:31:25 > > ---- ExifIFD ---- > > Date/Time Original: 2013:06:11 09:31:25 > > Create Date: 2013:06:11 09:31:25 > > ---- Sony ---- > > Sony Date Time: 2013:06:11 09:30:54 > > ---- GPS ---- > > GPS Date Stamp: 2013:06:11 > > ---- IFD1 ---- > > Modify Date: 2013:06:11 09:30:54 > > ---- XMP-exif ---- > > Date/Time Digitized: 2013:06:11 09:31:25 > > Date/Time Original: 2013:06:11 09:31:25 > > GPS Date/Time: 2013:06:11 14:31:25 > > ---- XMP-xmp ---- > > Create Date: 2013:06:11 09:31:25 > > > > Those who know better, please correct me if I am wrong. > > > > When I took the above photo, the time was recorded to the photo dependent on the time set in the camera. This is "2013:06:11 09:30:54." I imported the photos through GC to my computer and shifted the EXIF timestamp (Action> Metadata> Shift EXIF Timestamp, with the "Set the file date identical to the EXIF date" box checked) so the time matched that on my GPS. I then used GPSPhotoLinker to tag each photo with GPS data. > > > > Somewhere in this process, there is a bit of information recorded indicating the timezone of the photo. The only place I see this information in the above data is in the 3 "---- System ----" dates but the times indicated do not match any of the other EXIF times. > > > > Next, when I change timezones and access the photo again, the system takes the EXIF time and shifts it into the current timezone. > > > > Another point: I read in the Apple forums that "The Finder doesn't work with EXIF." Also in the forums: "...the dates are not actually carried in the file headers as numbers. They are special "date" fields, which are the number of seconds since a certain date (different OSs use different starting points). Whenever they need to be displayed, they're converted to what us mere mortals recognize as a date, using the system time zone settings." > > Much of the date/time issue is an OS issue, not GC. > > All Unix based systems use the same "epoch time." (OSX is Unix based) --- open a terminal window and type: "man time" then "man date" for all you might want to know about OSX. > > All "accessories" -- like GPS units and Cameras are also "Unix based." (I.e. POSIX/ISO standards compliant) > > The concept of "time zones" does NOT appear anywhere in the standards. It is up to the individual "user" (in this case, the OS) to maintain any time-zone information independent of the time field. > Note that "date" is also NOT maintained as pat of the time field... it too is a construct computed by the Operating System > > What is epoch time? > > The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of seconds that have elapsed since January 1, 1970 (midnight UTC/GMT), not counting leap seconds (in ISO 8601: 1970-01-01T00:00:00Z). Literally speaking the epoch is Unix time 0 (midnight 1/1/1970), but 'epoch' is often used as a synonym for 'Unix time'. Many Unix systems store epoch dates as a signed 32-bit integer, which might cause problems on January 19, 2038 (known as the Year 2038 problem or Y2038). > > > Time Synchronization is another whole kettle of fish. > OSX uses a protocol called NTP (Network Time Protocol) to set the date and time -- System Preferences/Date & Time. You can select "check date and time automatically" and define a "time server" -- the default is checked and Apple Americas selected. On the next panel "Time Zone" you can select -- "Set time zone automatically using current location" -- this is useful on a laptop that is "in transit" a lot -- but it also means that what you see for time zones "changes." > > A GPS may or may not use NTP to set and maintain its timestamp information. There is time information associated with basic GPS data as well as triangulation data from Cell Towers which is frequently used for GPS data. Again, the actual "timestamp" is stored in seconds since the Epoch. > > So, in short... a Timestamp -- is never seen by human eyes.... it's a 32bit signed integer. That is what the camera records, what the GPS records, what OSX records. What is DISPLAYED to you (the human) will change depending upon what filters you are applying to that 32bit signed integer. > > In the example above, the first 3 "time displays" include -0500 -- That might mean EDT... or it might mean CST - depending upon where you are and what the settings in your system are. None of the other displays contain that offset from GMT. > > Time on computers is both "relative" and "absolute," at the same time. It is a constant source of "fun" for us in the business. > > > > T.T.F.N. > William H. Magill > # iMac11,3 Core i7 [2.93GHz - 8 GB 1067MHz] OS X 10.8.4 > # MacBook Pro4.1 Core 2 Duo [2.5GHz - 4GB 667] OS X 10.6.8 > # Macmini6,1 Intel Core i5 [2.5 Ghz - 4GB 1600MHz] OS X 10.8.3 > > magill@... > magill@... > whmagill@... >

[ChromeAce]

Since you are in a different time zone now than you were when the image was taken, OSX is showing you the time the file was created in the time zone you're in NOW, which you think is wrong because it doesn't match the time you took it in the other time zone. But it is in fact, correct. To avoid these issues, some photographers choose to run their cameras and computers on Greenwich time and never change them. On Jul 7, 2013, at 4:19 PM, "Norm Siler" <normsiler@yahoo.com> wrote:   Thank you, Mr. Maglii. For instructing many more of us in both the technical points and the terminology to do so. My single point of question is the adjustment you suggest for CST and EDT. Here at approximately 90 West longitude, in the Central Time zone, I am accustomed during Standard Time months to applying a -0600 adjustment. During Daylight Time months, as now, I apply -0500 to GMT, one quarter of the 24 time zone globe from Greenwich. In no way diminishing my appreciation for your thorough explanation. Norm Siler --- In gcmac@yahoogroups.com, "William H. Magill" <magill@...> wrote: > > > On Jul 7, 2013, at 12:30 PM, iamabbqueen <captenaj@...> wrote: > > > > > > > Thanks to this discussion, I am understanding the different dates and times stored with an image much better. In looking at the EXIFTool by Phil Harvey data, the date/time items are: > > > > ---- System ---- > > File Modification Date/Time: 2013:06:12 19:04:42-05:00 > > File Access Date/Time: 2013:07:07 07:53:48-05:00 > > File Inode Change Date/Time: 2013:07:06 21:06:28-05:00 > > ---- IFD0 ---- > > Modify Date: 2013:06:11 09:31:25 > > ---- ExifIFD ---- > > Date/Time Original: 2013:06:11 09:31:25 > > Create Date: 2013:06:11 09:31:25 > > ---- Sony ---- > > Sony Date Time: 2013:06:11 09:30:54 > > ---- GPS ---- > > GPS Date Stamp: 2013:06:11 > > ---- IFD1 ---- > > Modify Date: 2013:06:11 09:30:54 > > ---- XMP-exif ---- > > Date/Time Digitized: 2013:06:11 09:31:25 > > Date/Time Original: 2013:06:11 09:31:25 > > GPS Date/Time: 2013:06:11 14:31:25 > > ---- XMP-xmp ---- > > Create Date: 2013:06:11 09:31:25 > > > > Those who know better, please correct me if I am wrong. > > > > When I took the above photo, the time was recorded to the photo dependent on the time set in the camera. This is "2013:06:11 09:30:54." I imported the photos through GC to my computer and shifted the EXIF timestamp (Action> Metadata> Shift EXIF Timestamp, with the "Set the file date identical to the EXIF date" box checked) so the time matched that on my GPS. I then used GPSPhotoLinker to tag each photo with GPS data. > > > > Somewhere in this process, there is a bit of information recorded indicating the timezone of the photo. The only place I see this information in the above data is in the 3 "---- System ----" dates but the times indicated do not match any of the other EXIF times. > > > > Next, when I change timezones and access the photo again, the system takes the EXIF time and shifts it into the current timezone. > > > > Another point: I read in the Apple forums that "The Finder doesn't work with EXIF." Also in the forums: "...the dates are not actually carried in the file headers as numbers. They are special "date" fields, which are the number of seconds since a certain date (different OSs use different starting points). Whenever they need to be displayed, they're converted to what us mere mortals recognize as a date, using the system time zone settings." > > Much of the date/time issue is an OS issue, not GC. > > All Unix based systems use the same "epoch time." (OSX is Unix based) --- open a terminal window and type: "man time" then "man date" for all you might want to know about OSX. > > All "accessories" -- like GPS units and Cameras are also "Unix based." (I.e. POSIX/ISO standards compliant) > > The concept of "time zones" does NOT appear anywhere in the standards. It is up to the individual "user" (in this case, the OS) to maintain any time-zone information independent of the time field. > Note that "date" is also NOT maintained as pat of the time field... it too is a construct computed by the Operating System > > What is epoch time? > > The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of seconds that have elapsed since January 1, 1970 (midnight UTC/GMT), not counting leap seconds (in ISO 8601: 1970-01-01T00:00:00Z). Literally speaking the epoch is Unix time 0 (midnight 1/1/1970), but 'epoch' is often used as a synonym for 'Unix time'. Many Unix systems store epoch dates as a signed 32-bit integer, which might cause problems on January 19, 2038 (known as the Year 2038 problem or Y2038). > > > Time Synchronization is another whole kettle of fish. > OSX uses a protocol called NTP (Network Time Protocol) to set the date and time -- System Preferences/Date & Time. You can select "check date and time automatically" and define a "time server" -- the default is checked and Apple Americas selected. On the next panel "Time Zone" you can select -- "Set time zone automatically using current location" -- this is useful on a laptop that is "in transit" a lot -- but it also means that what you see for time zones "changes." > > A GPS may or may not use NTP to set and maintain its timestamp information. There is time information associated with basic GPS data as well as triangulation data from Cell Towers which is frequently used for GPS data. Again, the actual "timestamp" is stored in seconds since the Epoch. > > So, in short... a Timestamp -- is never seen by human eyes.... it's a 32bit signed integer. That is what the camera records, what the GPS records, what OSX records. What is DISPLAYED to you (the human) will change depending upon what filters you are applying to that 32bit signed integer. > > In the example above, the first 3 "time displays" include -0500 -- That might mean EDT... or it might mean CST - depending upon where you are and what the settings in your system are. None of the other displays contain that offset from GMT. > > Time on computers is both "relative" and "absolute," at the same time. It is a constant source of "fun" for us in the business. > > > > T.T.F.N. > William H. Magill > # iMac11,3 Core i7 [2.93GHz - 8 GB 1067MHz] OS X 10.8.4 > # MacBook Pro4.1 Core 2 Duo [2.5GHz - 4GB 667] OS X 10.6.8 > # Macmini6,1 Intel Core i5 [2.5 Ghz - 4GB 1600MHz] OS X 10.8.3 > > magill@... > magill@... > whmagill@... >

[William H. Magill]

On Jul 7, 2013, at 5:19 PM, Norm Siler <normsiler@yahoo.com> wrote: > My single point of question is the adjustment you suggest for CST and EDT. > > Here at approximately 90 West longitude, in the Central Time zone, I am accustomed during Standard Time months to applying a -0600 adjustment. During Daylight Time months, as now, I apply -0500 to GMT, one quarter of the 24 time zone globe from Greenwich. That was my point ... -500 refers to Daylight time in one time zone and Standard time in the adjacent time zone -- simultaneously! --- it all depends on YOUR point of view. (I.e. which one you are located in. Eastern Daylight Time is -500; Central Standard time is ALSO -500. Put another way the "-500" refers to EITHER EDT or CST. It is NOT a fixed reference. OSX, as do most Unix based time systems, know all about the switch from Standard to Daylight times and change WHAT IS DISPLAYED to you accordingly, automatically doing the "Spring ahead, Fall back" change at 02:00. The fact of the matter is that change is "table driven" and when Congress changed the definition of Daylight Savings Time that table has to be updated. The last change was law in 2005 taking effect in 2007. "The federal law that established "daylight time" in the United States does not require any area to observe daylight saving time. But if a state chooses to observe DST, it must follow the starting and ending dates set by the law. From 1986 to 2006 this was the first Sunday in April to the last Sunday in October, but starting in 2007, it is observed from the second Sunday in March to the first Sunday in November, adding about a month to daylight saving time. " http://en.wikipedia.org/wiki/Daylight_s ... ted_States Time is a fun subject ... and I'm not even talking about Stephen Hawking's "Brief History of Time." T.T.F.N. William H. Magill # iMac11,3 Core i7 [2.93GHz - 8 GB 1067MHz] OS X 10.8.4 # MacBook Pro4.1 Core 2 Duo [2.5GHz - 4GB 667] OS X 10.6.8 # Macmini6,1 Intel Core i5 [2.5 Ghz - 4GB 1600MHz] OS X 10.8.3 magill@icloud.com magill@mac.com whmagill@gmail.com