CompositeImageExposureTimes and CompositeImageCount

[skibumdon]

Does any one have examples of these tags being used?  I searched the forums but the only thing I found was that it was unknown why they were added.

They can be of use in astrophotography where you do multiple long exposures and then stack them up, so for example you could do 90 60 sec exposures to get a 90 minute image. You can also tell the stacker to take say the best 95% of the images. Two examples are 1) DeepSkyStacker and inside Affinity Photo.

Unfortunately neither of these programs take advantage of these tags so I figured I would use exiftool to add them in to my stacked images. I want to make sure of the format though.

[Phil Harvey]

It looks like I didn't save a sample of this, sorry.

- Phil

[skibumdon]

The reason I asked is I was unsure of units.

In your tag section you have this:

0xa462    CompositeImageExposureTimes    undef    ExifIFD    (11 or more values: 1. Total exposure time period, 2. Total exposure of all source images, 3. Total exposure of all used images, 4. Max exposure time of source images, 5. Max exposure time of used images, 6. Min exposure time of source images, 7. Min exposure of used images, 8. Number of sequences, 9. Number of source images in sequence. 10-N. Exposure times of each source image. Called SourceExposureTimesOfCompositeImage by the EXIF spec.)

So if I expose for 60 sec per photo, do I could put in 1 or 60 but can't put an alpha in like 1 min.  I have tried on a test image. I should keep the units the same for each of the fields in this tag, which I guess should be seconds so it stays as an integer.

Here is an example:

Code Select Expand

exiftool -CompositeImageExposureTimes="60 sec 59 min" -CompositeImageCount="59 59" test.tif
Warning: Argument "min" isn't numeric in numeric eq (==) in CompositeImageExposureTimes (RawConvInv) - test.tif
    1 image files updated

[StarGeek]

From the Exif Version 2.32 specs (emphasis mine)

SourceExposureTimesOfCompositeImage
For a composite image, this tag records the parameters relating exposure time of the exposures for generating the said composite image, such as respective exposure times of captured source images (tentatively recorded images). The unit is seconds (sec).

The EXIF tags page says CompositeImageExposureTimes is 11 or more values.  These would be each individually set.  In your example, you're trying to set the 2nd value to sec and the fourth value to min, which is why there's an error.

The correct way to set 60 seconds/59 minutes would be

Code Select Expand

C:\>exiftool -P -overwrite_original -CompositeImageExposureTimes="60 3540" y:\!temp\Test4.jpg
    1 image files updated

C:\>exiftool -G1 -a -s -CompositeImageExposureTimes y:\!temp\Test4.jpg
[ExifIFD]      CompositeImageExposureTimes    : 60 3540
Edit:  There's a link at the top of the EXIF tags page to the EXIF spec PDF file at Archive.org

[skibumdon]

Thank you very much!!