Hi Thomas, One thing you could do (I know this is quite easy to do in Matlab so I assume it owuld be in R as well) would be to export a movie with a timestamp on the images if they aren't already timestamped. Then watch the movie and note the spots where something happens, then refer back to those images. This assumes the images are timestampped in the name or you can pull the capture time info from the jpg exif data. Again, this is pretty easy to do in other programs so I'm assuming someone has written code to do this in R or Matlab. It also assumes that "events" are not too common so manually finding the selected images isn't to onerous.
One issue you want to be aware of is making sure that your cameras have the time set correctly. Many game cameras just give the images sequential names as they ar captured (like img_123.jpg, etc), so you have to manually rename them so the image names have a timestamp in them. you can skip this step but it can be really hard after the fact to figure out what images you are dealing with if they don't have timestamped names, particularly if you have lots of cameras and are juggling SD cards with different sets of images on them. We wrote a windows app that does this (see below) but I bet you could write a quick script in R to do it as well. I agree there is probably existing code for finding motion in the images. At the very least you could start with a simple algorithm that subtracts the color values of each image from the previous one and then sums the total value left over. Then test what threshold value accurately flags the images you want. You can also use the sum of all rgb values to eliminate nightime or too dark images etc. But I agree with the other comment that you probably want to run through them all at least once to make sure you didn't miss anything. If you have software like Adobe after effects (or the Mac equivalent), you can also load all the images as a timeseries (they provide this feature for people doing timelapses), then just scroll through the movie with the timebar and note what images have movement in them. Video editing software also provides options for marking key points and exporting single images so you could come up with a pretty easy work flow this way. This would probably be the easiest way to do this if you aren't going to automate it. I think you can also load pretty large image sets into quicktime pro and do the same thing. Email me if you want a copy of our naming utility (for windows). It takes any number of time-series images, extracts the timestamp from their exif data and renames them with correctly timestamped names in time-series folders. It works great but since it is optimized for higher framerate timelapse and use by our timelapse software it does put everything into folders by hour which can be annoying if you don't have that many images per day. You also have the option to stick them all in one folder. Cheers, Tim --- Tim Brown http://Time-Science.com <http://time-science.com/> - Advanced Ecological Imaging http://www.gigavision.net - Gigapixel timelapse systems [email protected] (801) 893-1314 | (866) 411-3836 <http://www.linkedin.com/profile/view?id=13027940> <http://timescience.wordpress.com/> <https://twitter.com/#!/timescience>
