Archive | May, 2011

How to Record DPL Projectors without Flicker

28 May

Shooting a projection screen to record a PowerPoint presentation is something you maybe required to do. While there are numerous alternatives to shooting the screen, many of us doing video production in Education are forced to shoot the screen on a regular bases. This posses a number of challenges (white balance, exposure, etc). However, I’ve noticed that one problem that can sometimes stump videographers: what to do when the projection is flickering.

Flickering projection is a common problem you’ll encounter whenever you point a camcorder at an image from a DLP projector. You won’t get the same kind of flickering from LCD projectors, as these two types of video projectors have some key differences. LCD projectors continuously projects an image, while DLP projectors use a spinning color wheel to project one color at a time. The color wheel spins so fast that to your eyes it looks like one image. The camera however is not as easily fooled as your eyes.

How do I know when I am shooting a DLP Projector?

While you could try to Google the projector’s model number, the easiest way to know is to look at the projected image through your camera. If you see a flicker through the camera, but not with your naked eye, then it’s a DLP projector. If you see a flicker with your naked eye, then it’s a problem with the projector.

How can I record a DLP Projector without recording the flicker?

All you need to do is to adjust your shutter speed. In my tests, there is no flicker at 1/60. Remember your shutter speed isn’t related to frame rate. If you are filming at 24 frames a second, a 1/60 shutter speed means that each of those frames is exposed to light for 1/60 of a second. If you exposed a frame to light for longer the camera records multiple cycles of the color wheel. And if you exposed a frame to light for less than 1/60 of a second, it would record only part of the color wheel.

What does this look like?

The video below shows the image from a DLP projector at a variety of frame rates. WARNING: the second half of the video features some very intense flickering. Watch at your own risk.

DLP Projectors Shutter Speed Test from Kevin McGowan on Vimeo.

Stabilization Test: SmoothCam vs. Warp Stabilizer

11 May

Screen shot 2011-05-10 at 5.42.43 PM

Adobe After Effect CS5.5, released just a few days ago, has a new video stabilization tool call “Warp Stabilizer”.  After watching some impressive looking demos, I wanted to try out the new tool myself.  What makes this tool more interesting than some other options out there is that Warp Stabilizer can correct some of the rolling shutter and “jello” issues that occur with DSLR video.  When I’ve used stabilizing software on DSLR footage in the past, I gotten images that were steady, but had major distortion.

For testing I found some very shaky outtakes from a music video shoot on my GH1 last year.  I’ll say right off the back that there is a simple fix for all of these shots:  use a tripod.  Stabilization software is not a replacement for a tripod.  That being said, what I wanted to test is if warp stabilization could save any of these unusable clips.  The video below plays four clips, each three times.  The first time the clip is played it is the original footage. The second it’s the same clip with Final Cut Pro 7′s SmoothCam filter applied.  And the third time it’s the clip with After Effect’s Warp Stabilizer.

 

 

SmoothCam vs. Warp Stabilizer from Kevin McGowan on Vimeo.

The Results:

Clip 1
Smoothcam levels out the shot, but adds jitters near the end.  WarpStabilizer makes the shot completely level, without any jitters.  However, the resulting image is a little softer.  I believe this was caused by turn WS’s  ”Rolling Shutter Ripple” to enhanced reduction.  Changing this setting removed some warping effects I was seeing, but had the side effect of changing the image.

Clip 2
Both Smoothcam and WarpStabilizer fail to make this shot usable.  The shot is very shaky and the camera moves at near the same time as the subject moves, which further confuses both stabilizers.  When I attempted to use WarpStabilizer to remove the “jello” the results were awful.  For WS to fix jello it needs to be able to detect the fore-ground and back-ground of a shot.  Since the actor in this shot is right up against the door, WS can’t tell which is which.

Clip 3
WarpStabilizer makes the camera movement a litte smoother than Smoothcam in this shot.  In general, stabilization software crops your shot.  WS has a feature called “Synthesize Edges” which will re-draw the edges of your frame so you can avoid cropping. It did work well on this shot, because one of the musician’s faces is right at the edge of the frame.  The lesson here, if you are going to be doing any stabilization, don’t have anything important happening on the edge of your frame.

Clip 4
I was very impressed with how WarpStabilizer saves this shot.  In this shot, WS can easily tell the difference between the foreground and background (even with the rack focus).