Graphically verifying time-lapse intervals using ExifTool (and Excel)

Timestamp plot - annotated

Here’s a quick and easy way to check time-lapse intervals using a combination of ExifTool, (a great command-line application for reading and writing image EXIF data) and a program such as Excel to process and plot the data.

Checking the interval between each shot can be a good move, particularly for long time-lapse projects where equipment may malfunction, or when you just want to know that you haven’t missed a file when exporting your images.  Consistent intervals are (generally) what we want, and any significant variation might appear as stalls or skips in the final movie.

For example, the figure above plainly shows the issues I encountered when attempting to shoot a time-lapse of the Transit of Venus last year.  I ended up dropping a few frames due to battery failures and shutter lock-ups.  A problem I’m yet to tackle!

Anyway, here are the three steps to graphically displaying your time-lapse intervals:

1. Get the timestamps

The first step is to ask ExifTool to write a csv file containing the timestamp of every image in the time-lapse sequence.  This is done using the terminal command below.  In this case, the images are located in a folder or directory called “frames” and the output file produced will be called “timestamps.csv”.

exiftool -csv -DateTimeOriginal frames > timestamps.csv

2. Parse and process the timestamps

All that remains is to parse the text in the csv file in order to get time values which can be manipulated.  I did this in Excel: Columns A and B were produced by ExifTool; Column D uses the =MID function to read the final 8 characters of the time stamp; Column E converts this string into a time with the =TIMEVALUE function; and finally, column F subtracts each image’s timestamp from that of the previous image, to give a value for the interval.

Calculating time-lapse intervals with Excel

Spreadsheet programs like Excel can parse the timestamps and calculate the shooting intervals

3. Plot the intervals

Lastly, just plot the time stamps vs. the intervals on a scatter chart and any dodgy interval will stick out like a sore thumb.

Excel timestamp plot

Plotting the image timestamps vs. the shooting interval can highlight problems; if all is well then you’ll just see a straight line :)

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