Secrets Q & A
- Written by Chris Eberle
- Published on 30 April 2014
I shoot my home movies with a HighDef camera and it offers me the option of 60i or 60p. Is there any advantage using one or the other as to how it will appear on my HighDef Flat Panel Display?
- Ron S
The question of 60i (interlaced) versus 60p (progressive) brings up several considerations. And the first part of the answer is that one is not necessarily better than the other.
You're correct to consider your output device when shooting video. Watching video on a television versus your computer or a mobile device will influence how you film. We'll start with a quick refresher on video encoding.
Interlaced video is what we all watched back in the CRT days, and it was simply because of technological limitations. Interlacing is a technique that virtually doubles the frame-rate of video in order to consume less bandwidth. In the case of 60i, each frame contains either the odd- or the even-numbered lines of the image. To the eye, you're watching 60 frames-per-second rather than 30. We're still stuck with interlacing in most hi-def broadcasts which are 1080i; although FOX is a notable exception at 720p.
Progressive video is what all digital displays render today. Each frame is scanned top to bottom with ever line present. Obviously this requires twice the bandwidth to maintain an equal bitrate. If one has the infrastructure to support said bandwidth, progressive video will always look better because the display doesn't have to do any processing of the incoming signal. What goes in is what comes out.
When shooting home video, storage is probably the biggest issue to deal with. Simply put, video shot at 1080/60p will require twice as much space as that shot at 1080/60i. And sending interlaced footage to your HDTV means the content must be de-interlaced before its output to the screen. Depending on the quality of your display, that might not be a problem or it could introduce combing and line twitter artifacts as the TV stitches the interlaced frames into progressive ones. Check out the example below.
When filming motion, interlaced frames are not perfectly registered to one another when the time comes to combine two into one. A TV with good video processing can fix this error but most displays I've reviewed fail this test. It's called 2:2 pulldown and very few TVs or disc players can do it properly. Oppo's Blu-ray players are the best-known exception.
So the answer is if you have the storage, always shoot progressive video. But there is one more thing to consider. Shooting at 60 fps will make your video look very smooth, like a soap-opera. Consider that even though Hollywood has largely gone digital and can shoot at any frame-rate they want, they still shoot primarily at 24 fps. Of course, motion resolution is better at higher frame-rates but to most people it just looks un-natural. I think 60p video looks flat and phony compared to film. But that is my personal preference.
By the way, 24p takes less storage space than 60i! And make sure your HDTV can handle 24p correctly. Most 120 Hz LCD panels will repeat each frame five times if you turn off the interpolation (often called things like MotionFlow).
I'll wrap this up with my recommendation. Buy plenty of storage so you can shoot progressive video all the time. If you're filming an artistic subject; kids growing up, family time; try 24p. If you're shooting fast action like sports, go for 60p.
- Chris Eberle, Senior Editor