purpose: Will Kahn-Greene's blog of Miro, PyBlosxom, Python, GNU/Linux, random content, PyBlosxom, Miro, and other projects mixed in there ad hoc, half-baked, and with a twist of lemon
S and I decided to get a wedding photographer in addition to allowing
our guests to take as many photos as they wanted of all aspects of our
wedding (except when we were getting dressed [and ... undressed]).
There were a few reasons for this one of which being the several horror
stories we've heard about people's digital media dying causing them to
lose all pictures of their wedding. Ick.
The problem is that there are a fajillion pictures and it's really
hard to order them into a single consistent timeline. The wedding
photographer we had1 had four cameras and took some 800
pictures. My dad took another 100 or so. Other people took a bunch,
too. Right now I'm working with 1200+ pictures all of which are pretty
big (between 5 MB and 10 MB each). It's not feasible to tweak them all
by hand to order them. I didn't want to leave them unordered--my soul
shudders at that thought. I needed a way to do batch processing to
reorder pictures from a bunch of cameras into a nice timeline.
More after the break...
----
First thing I did was put all the pictures that had no EXIF information to
the side. There weren't many of them and I don't see any way to batch
process them.
We're now left with 1000+ pictures all of which have EXIF information that
we can work with. Interesting properties of the problem:
- all of the pictures have DateTimeOriginal and SerialNumber headers
in the EXIF data
- pictures from a single camera have a consistent timeline in the sense
that if picture 2 from camera A comes before picture 3 from camera A by
14 seconds, then that's what happened
- the time from all the pictures from camera A are a constant offset
from all the pictures from camera B
This is all pretty obvious and there's nothing exciting here, but it does
reduce the problem to picking a camera as a baseline and then figuring out
how far off in seconds and minutes the other cameras are from the baseline.
That's pretty easy.
First thing I do is get
exiftool and
run it like this to rename all the files according to their timestamp
and serialnumber:
exiftool '-FileName<${DateTimeOriginal}_${SerialNumber}.jpg' \
-d "%Y%m%d_%H%M%S" .
Then I copied all the files into a thumbs directory and
in the thumbs directory I used mogrify which comes with
ImageMagick
to create thumbnails:
for i in `ls *.jpg`; do mogrify -quality 65 -geometry 150; done
Then I did this to figure out all the serial numbers of the cameras
that took these photos:
exiftool -SerialNumber *.jpg | sort -u
Then I wrote a Python script (any language will do) to build an index
of the images using timeline offsets:
import os, time, datetime
# serial number -> (offset(minute, second), color)
OFFSETS = { "1020415017": ((0, 37), "#ff5555"), # red
"1420918126": ((1, 11), "#ff55ff"), # purple
"1621009923": ((1, 9), "#55ff55"), # green
"620306618": ((0, 0), "#5555ff") } # blue (baseline)
def getinfo(fn):
t = fn.split("-", 1)[1]
t = t.split("_", 1)
cam = t[1]
cam = cam.split(".")[0]
t = t[0]
print fn, t
t = time.strptime(t, "%H%M%S")
# hardcoded year, month, and day
t = datetime.datetime(2007, 05, 26, t[3], t[4], t[5])
offset = OFFSETS[cam][0]
t = t - datetime.timedelta(0, offset[1], 0, 0, offset[0])
return (t, cam, fn)
def build():
files = os.listdir(os.getcwd())
files = [f for f in files if f.endswith(".jpg")]
pics = [ getinfo(fn) for fn in files ]
pics.sort()
out = open("index.html", "w")
out.write("<html><body><table border=\"1\">\n")
for t, cam, fn in pics:
out.write("""
<tr><td>
<table>
<tr><td bgcolor="#aaaaaa">name</td><td>%s</td></tr>
<tr><td bgcolor="#aaaaaa">camera</td><td bgcolor="%s">%s</td></tr>
<tr><td bgcolor="#aaaaaa">datestamp</td><td>%s</td></tr>
</table>
</td><td><img src="%s"></td></tr>""" % (fn, offsets[cam][1], cam, repr(t), fn))
out.write("</table></body></html>")
out.close()
if __name__ == "__main__":
build()
Note that I color-code the cameras. I find this makes it really easy
to eyeball the timeline without trying to distinguish between
similar-looking serial numbers.
I run that in my thumbs directory and it builds an index.html
page that I can look at with a web-browser. The index.html has
the offsets factored in. I look through the pictures and tweak the
offsets until all the cameras are consistent with one timeline. Once I
have a final set of offsets, I go through the pictures for each camera
and (very carefully) do this:
exiftool "-AllDates-=0:0:0 0:M:S" *SN.jpg
^ ^ ^^
replacing:
- M with the minute offset,
- S with the second offset, and
- SN with the camera serial number
Then you do another pass at renaming files and the files should then
be in the same consistent timeline and in alphabetical order by filename.
After I worked out the process it took a couple of hours. We had the
advantage of having a couple of points during the wedding where a lot
of photographs were taken and it was obvious as to what order they needed
to be in.
06/21/2007 - Changed the title to something more appropriate. I was thinking
"fix" because I was modifying the EXIF metadata for each photo to put them
in the correct order, but
Konquest makes a good point. I also fixed one of the command lines.
06/22/2007 - bockris said in the reddit.com comments:
This is a good idea. I've had to fix the EXIF data my photos before
because I changed the batteries and didn't reset the date but I've never
tried to sync up multiple cameras after the fact.
If I'm ever in a similar situation as the OP, I think I have everyone
take a picture of a clock with a second hand at some period during the
event. That would let you easily get the time difference among all
cameras.
Copyright 1996 to 2012, Will Guaraldi Kahn-Greene, under the Creative Commons BY-SA 3.0 license
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