Saturday, March 27, 2010

timelapse in Cinelerra

I've been playing around for the past few weeks with DSLR Remote, an iPhone app that allows you to control recent Canon or Nikon cameras remotely. DSLR Remote has an intervalometer, or timer, to allow you to take N number of photographs at T intervals. Once you take a bunch of photos, you can assemble them in Cinelerra to create a video of the change seen over time in the pictures, or timelapse.

This is my first experimentation with timelapse; specifically, timelapses of clouds and nighttime city scenes. I'm using a Canon 5D Mark II. Timelapse has been a real challenge, as the camera must be setup for proper exposure. I'm generally satisfied with the result, but I think it can be improved upon once I figure out the proper exposure settings.

An Education
I have learned some basics over the eight or so timelapses I've done:
1) don't use Automatic mode or full manual because the exposures vary quite a bit if the aperature (F Stop) or shutter speed change dramatically or conversely, don't change. Use aperature priority mode instead. Also, if the camera is in Auto mode, sometimes it will take time to change its settings. This will change the time interval between shots and make your final timelapse production jump around and jerky.

From the EXIF data in the JPEGs that I took during a morning timelapse, you can see how my shutter speed bounces around as the sun rose over a period of about an hour (FStop and ISO were locked):
[mule@ogre cinelerra]$ ./ /mnt/videos/projects/timelapse/Remote04639.jpg
exif:ExposureTime: 1/5
exif:FNumber: 11/1
exif:ISOSpeedRatings: 640
[mule@ogre cinelerra]$ ./ /mnt/videos/projects/timelapse/Remote05639.jpg
exif:ExposureTime: 1/100
exif:FNumber: 11/1
exif:ISOSpeedRatings: 640
[mule@ogre cinelerra]$ ./ /mnt/videos/projects/timelapse/Remote06239.jpg
exif:ExposureTime: 1/500
exif:FNumber: 11/1
exif:ISOSpeedRatings: 640

This can also blowout highlights and generally wash out the colors in the image, as shown in the latter half of this video:

2) shoot in aperature priority mode with auto ISO on. Auto ISO will account for variations in lighting conditions, like when a cloud passes in front of the sun.

3) make sure any lens stabilization is turned off, as this will make the frame jump around at times. This sounds counterintuitive, yes, but if the camera is on a tripod (as it should be for timelapse photography) a lens stabilizer will try to correct for movement that isn't present and will shift the frame around slightly. I figured this out after about five tries. (Yes, I am a doofus).

4) turn off automatic white balancing as it will effect the exposure from frame to frame

5) if you want to emphasize depth of field during day timelapses, make sure to get a neutral density filter. This will allow you to keep your aperature open wider, thus creating greater depth of field.

6) slower shutter speeds slightly blur movement. For example, daytime time lapse photography of clouds seem smoother with a slower shutter speed. Again, try a neutral density filter to help slow down the shutter speed. Of course, slow shutter speeds are very cool for time lapse traffic shots.

7) make sure your intervalometer is functioning properly. If it doesn't accurately time the snapshots, your final timelapse will look jerky and jump around once stitched together in Cinelerra.

Proper Interval
My camera has a limitation of 999 total shots that can be taken. In my experiments, I found that to acheive a smooth movement of clouds in my timelapses, I should take a picture every two or three seconds. That means if I want to take a picture every two seconds (30 pictures per minute) and I have 999 total shots available, my timelapse will last for a period of 33.3 minutes (999 shots / 30 pictures/minute). Doesn't seem that long, does it? If I chose an interval between shots of three seconds, my timelapse would occur over 49.95 minutes (999 shots / 20 pictures/minute). That seems a little more useful.

Timelapse in Cinelerra
Once I have my 999 images, I then stitch them together in Cinelerra at 60fps, 30fps or 15fps depending on my desired, medium or slower motion of whatever I was time lapsing. You'll need to do a bit of calculation to figure out at what duration (length) the images will be once imported into Cinelerra. That duration is set in Preferences -> Recording (screen below). I've provided those calculations below:
15 seconds = .0667
30 seconds = .0333
60 seconds = .0167

Be aware that if you import that many JPEGs, and especially if the JPEGs are very large, the import can take a while. My source files were 5616x3744 and took about 15-20 minutes to load.

Here's my acceptable timelapse..not the best..but getting there:

Going forward, the one thing I'd like to acheive is to remove or limit the slight changes in exposure that occur every once in a while so that the timelapse flows smoothly from one frame to another.

another work in progress..
the mule

Canon 5D: Best Modes for Video and Photos