TV Specs Demystified: Frame Rates
TV Specs Demystified: Frame Rates
aka scan rates or refresh rates
1080 – 24P – 60P – 120Hz – 240Hz – 480Hz
So you’re shopping for a new 1080P flat panel TV to update your home theater system and one of the many confusing terms you’re seeing on all of these TVs are 24P, 60P, 120Hz, and 240Hz. And that’s not the end of it. 480Hz is on the immediate horizon and there are a few plasma TVs boasting “600Hz Sub-field drive”.
Well like almost everything else in life, it’s not what you do, it’s how you do it. 600 is only better than 60 if you do it right.
A little background in case you’re not a videophile. 24P means 24 frames per second (fps). That is the frame rate that most Hollywood movies are filmed in. So every second of a movie is actually made up of 24 individual pictures. TV is a little different. Most TV shows are filmed at 30 frames per second. The people in charge will tell you that there are very good reasons for the difference, but they’re full of crap. They did it to screw with us.
The difference between 24 and 30 frames per second used to be a big deal in the days of CRT “tube” TVs, because they sucked, but now with today’s TVs, there is a little less sucking going on. Today’s TVs have no problems switching between 24 and 30fps, but even if you play back 24fps just as it is supposed to be, it looks a little choppy. Well the people who make the TVs are smarter than the people who make the movies we watch on them, right? Of course they are. So they decided to screw it all up and gave us 120Hz.
By the way, Hz, is short for Hertz, which is a measure of frequency over the course of one second. It is named after German physicist Heinrich Hertz. He was smart way back when chicks thought it was cool to be smart. If you didn’t graduate elementary school, frequency means how often something happens over a given duration. The rate at which the Earth circles the sun is measured in a frequency referred to as a year.
So now that you know frequency, you know that Hertz and frames per second are the same thing, so 24fps = 24Hz, right? Wrong. The reason they call it Hz, and not fps, is because they aren’t really showing you 120 unique frames each second. They are just taking the 24 or 30 original pictures each second, multiplying them, occasionally tweaking them, inserting a few all-black “dark frames” here and there and making that mess of crap add up to 120. So there’s a shred of honesty in the “120Hz” moniker, though I have a feeling it wasn’t done on purpose.
So now that we’re friends, and you know I’m not BS’ing you, I can let you in on a little secret. 1080/60P is really 1080/30P, and pretty much any time you see plain old 1080P on a TV set, they mean 60P … or rather 30P because they’re just taking the 30-frame image and showing it twice. Well that little trick gave them an idea.
Since there is no good way to convert Hollywood’s 24fps into TV Land’s 30fps without doubling every 4th frame (aka 3:2 pulldown) and causing judder, the TV manufacturers remembered a trick from their 4th grade math class called the “lowest common multiple“. Guess what’s the LCM of 24 and 30? Yep, it’s 120. Going to 120Hz made all the image processing much easier. For 24fps film sources they have 5 cycles to work with on every frame and for 30fps video sources, they have 4 cycles. To take advantage of this, they can just flash the same image 4 or 5 times, they can insert full black frames into the mix, or if they have a lot of video processing horsepower, they can actually interpolate intermediate frames to smooth out the motion.
Most manufacturers are taking some mix of all of these options and making their own recipe to create the 120Hz image. Some do it better than others and some are just downright bad. But in my opinion, none of them have perfected 120Hz yet, so I am baffled by the new 240Hz sets already out and especially by the 480Hz that will be here any day now. Most LCD TVs are technically incapable of even displaying 480 unique frames in one second, even good ones. It requires a 2 millisecond (2ms) response time (1/480 = .002), which is not impossible, but certainly not common in the world of LCD TVs. Just a few years ago, an 8ms response time was a big deal.
Now there are a few plasma sets branded with various forms of 600Hz marketing taglines, but most are not as advanced in terms of video processing as the better 120 or 240Hz LCD sets. I am sure that there is some technicality that lets them legally call it a “600Hz subdural hematoma” or whatever, but for the most part, it’s marketing.
Summary: The reason we have all these different frame rates is because there’s no good way to convert film’s 24 frames per second to TV’s 30 frames per second. And even if there was, 24 frames per second is still a little choppy when stuff moves. So the TV manufacturers wanted to kill two birds with one stone. 24 x 5 = 120 and so does 30 x 4. That works out quite nicely. But everything about TVs is a bogus numbers-based pissing contest so 120 led to 240 which led to 480 even though it’s not technically possible. No one has managed to perfect 120Hz yet, much less 240Hz. Some of them look good, dare I say very good. But even those are far from perfect.
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