24P cinema mode

The new 1080p home theater equipment has finally been installed and can be enjoyed. After bathing and burning incense, you are ready to enjoy your favorite classic old film Casablanca, with unprecedented clarity and contrast, as if you have never seen it before. Your Blu-ray player outputs 1080p/24, which is a signal format that everyone is crazy about. You have purchased the Blu-ray version of Casablanca. Your 1080p projector displays the signal from the Blu-ray player in the original 24 fps format-everything is as pure and perfect as possible.

So, you pressed the play button. The logo of Warner Bros. appears on the screen. The earth turns very slowly. The map of the Mediterranean is presented to you with amazing clarity. Very satisfied with the new system, you smiled. Then-something unexpected happened. In the two minutes and three seconds of the movie, the camera is on the horizon in stop for a minute, and then it slowly rolls down the street view. You shrink back in horror because the picture becomes stark raving mad. The picture stuttered and trembled like a crazy madman. The building seems to be struggling in a strange earthquake. It's painful to watch this kind of thing. You blinked in disbelief. Your brand-new super-class 1080p projection system, pure original 24p transmission, how can it make people so unhappy?

Welcome to the world of 24p. What you have just experienced is called motion jitter, an extremely annoying defect. Originated from the film is made at the speed of 24 frames per second (fps). 24p sampling rate is adopted as the de facto standard in 1926. The film industry, which was in its infancy at that time, realized that they needed a fast enough sampling rate to support synchronous audio tracks. (The first talking movie "Jazz Singer" was released on 1927. Before talking about movies, the speed of movies was even lower, partly to save film and partly because the exposure speed of films was much slower at that time.

Since then, the film industry standard of 24fps has been a heavy burden for us. As we can see, this rate is too slow to analyze the panning clearly. Therefore, when the "focus plane" is translated at an inappropriate speed, you will see that the motion is shaking. Sometimes, there are so many tremors that you can't see everything. Unfortunately, your high-resolution 1080p/24 system can only display pictures in the original form encoded by Blu-ray disc. Before Blu-ray and HD DVD appeared, we had never seen such a primitive 24p at home.

In fact, even in commercial cinemas, we have never seen such an original 24fps movie, because the double shutter action of the cinema projection system reduces the experience of tremor and flicker. You can see some tremor in the cinema, but compared with the digital home theater projector that plays blue light or HD DVD at 24p, the tremor is not as obvious as the latter.

Wait a minute, wait a minute, you said ... "I used to think all these trembling problems were related to the 3:2 pulldown. Once we use 24p, we can get a clear image. " Well, many people have this expectation, because until recently, everything we saw in the NTSC world was that 24 fps movies were converted into 30 fps displays. This conversion from 24 fps to 30 fps (usually called 3:2 pulldown) does introduce a slightly different jitter and some blur when the lens is translated. Therefore, it is natural to expect the original signal to look better without being damaged by the annoying 3:2 pulldown.

The result tells us that it is common for things to go against our wishes. The motion jitter of the original 24p may be quite bad. If you have equipment, you can test it yourself. Suppose you have a Blu-ray player, you may have a copy of "casino royale" instead of "Casablanca". If you have casino royale, find a messy scene in it. There are many such scenes, but there is a classic in Chapter 9, which starts with 1 hour 1 1 minute 13 seconds. The dealer is dealing cards, and the camera slowly shakes the table.

In the 24p replay, this scene is pure and complete disaster. People around the table are divided into pieces, tuxedos are flashing, and casino royale's logo on the table is flashing like neon lights. When you play this clumsy clip many times, switch your Blu-ray player to 60p output and watch it again. Yes, it's still a mess But if you look closely ... the flutter effect actually decreases. This is because the 3:2 pulldown blurs and masks some potential motion jitter in the movie. Of course, the transition tremor caused by the 3:2 pulldown has also joined this visual disaster, but strangely, it works in a mutually exclusive way with the potential 24p tremor. After adding the two, the final effect is that the image is a bit blurred and the total jitter is obviously reduced. The above scene looks bad at 60p, but it looks worse at 24p. After all the hype about 24p (like almost everyone, we eagerly expected the benefits of 24p), we must admit that from the final analysis, 60p replay is a less disturbing replay method for many people.

Since we have been told that 3:2 pull-down tremor is the root of all evil, it is really shocking to hear that it is not the biggest misfortune suffered by home theater enthusiasts. In fact, however, the old sampling rate of 24 frames per second is a more essential problem. It's no secret. Professional cinematographers deeply understand the defects of 24 fps capture rate. In order to minimize the impact of vibration, they try their best to control the camera, because the director doesn't like vibration like us. The common technology is to set the camera on the track to make it move at the same speed as the moving object, so that the object always stays in a fixed position in the image frame. If an object does not pass through the screen, it will not vibrate. However, if the background moves in the opposite direction to the object, the background will vibrate.

If the casino royale CD is still in your Blu-ray player, you can observe a good example discussed above. Go to chapter 9, 1 hour 9 minutes and 6 seconds. Bond is walking through the hotel. Note that the photographer placed Bond in the right half of the image frame. When Bond approaches, the camera backs off, so that when the background moves, Bond stays in a fixed position. Bond turned to the right, and the photographer continued to keep him in the right half of the image. When playing the scene in 24p, Bond remained stable and clear, while the background trembled wildly. When you play back this passage at 60p, the background tremor still exists, but it is reduced-it is more tolerable.

Please note that the distant background in this scene is out of focus to some extent. Under similar circumstances, photographers can use a larger aperture to minimize the optical depth of field of the camera. In this way, they can focus on the foreground object and deliberately defocus the background. This makes the motion jitter in the background less obvious to the observer. In this particular scene, they didn't fully achieve this goal, but they played a role.

Therefore, we can draw two basic conclusions. First of all, motion jitter is a by-product of the 24 fps shooting rate. If you play Blu-ray or HD DVD movies with 24p transmission, you will see motion jitter. How much motion jitter you can see is directly related to how many medium-speed panning scenes there are in the movie. Secondly, the 3:2 pull-down conversion is the secondary source of jitter. However, the 3:2 pulldown tends to blur and soften the strong motion tremor you see in the original 24p monitor. Aside from the widely accepted view, don't be surprised if you can choose to play Blu-ray movies in 24p or 60p, and if you prefer the relatively stable 60p.

So, what can be done to get rid of the tremor?

There must be. One solution is called frame interpolation. But before we start this topic, let's clarify the root of the problem: in the panning scene, the picture will shake because the standard sampling rate of 24 frames per second is not fast enough to fully analyze the action. If we shoot a movie at 60 fps and play it back at 60p, the tremor defect may disappear.

What would it look like if the film was shot at a much faster sampling rate? Frame interpolation is a process that the projector (or video processor) approaches the above situation. What it does is to cache more than two consecutive image frames and calculate the motion change between the two frames. This information is then used to create intermediate frames as part of a sequence of actions between real frames. For example, the "Frame Creation" system of Panasonic AE3000 will pre-evaluate two or three frames (depending on the mode you choose) and generate three intermediate frames, each of which is a 25% incremental step of the action between two real frames. These frames are output at a rate of 96Hz. So in fact, every 1/24 seconds, what you actually see on the screen is an original frame from a Blu-ray disc, and the next three "motion adjustment" intermediate frames, which are displayed in turn at a speed of 96Hz. In other words, when using the frame creation mode of AE3000, 75% of the total image information on the screen is not from the Blu-ray disc at all, but is generated by the projector!

The result is that when you watch Casablanca, you reach the point where the camera rolls from the horizon to the street view. The picture is smooth, stable and clean, without any trace of motion tremor. After reading its comparison with the regular 24p broadcast AB, there is no dispute. One presents a visual nightmare, and the other brings you a smooth and clean image. This fall, Panasonic is not the only manufacturer offering frame interpolation on its home theater projector. Several other models also provide similar functions. Including Sanyo PLV z 3000 and several Epson home theater models. Different manufacturers have different methods to realize frame interpolation. But they all solve the basic problem of movie jitter by generating intermediate frames to represent small steps in the middle of the action sequence. Either way, they can make you feel how people feel when the film is shot at 60 fps.

As a warning, we need to point out that frame interpolation is a brand-new function of home theater projectors. Because of this, this function may introduce some flaws until (after several generations) the problem is gradually solved. So far, the only model we have seen with this function is Panasonic AE3000, and we haven't seen any defects that can be attributed to the frame creation system. However, frame interpolation does increase the video delay of AE3000, which we think is the same on any model with frame interpolation function. Therefore, in order to solve the problem of mouth synchronization, users will want to add an audio delay to the whole system.

Now, before we come to a conclusion, it is very important to admit the fact that many video lovers today prefer the tremor in the 24 fps movie viewing experience. For some movie fans, tampering with natural vibration is a crime. This is because, without the inherent instability of low sampling rate, the movie doesn't look like a real movie. Indeed, they are right. It really doesn't look like a real movie. Frame interpolation technology will make the picture look very clean and stable. If you can't get used to this feeling, it will make you nervous. (Because of this, AE3000 makes it an option, and you can turn it on or off at will. )

But consider the fact. In early silent films, there was no standard exposure rate for image frames. The photographer manually turns the crank of the camera to expose the film at a speed of 12 to 24 frames per second or higher. The ideal goal of professional projectionist in cinema is to play back the film at the speed of exposure and make the action more natural. However, nine times out of ten, cinema managers want the film to be shown faster than the exposure speed. After all, even then, time was money. And to be honest, some movies are played at a proper speed, which really has better entertainment effect. Man-made quick action is the aesthetic taste that the majority of movie audiences flock to. Sometimes, when action movies or comedies are shown at the speed of shooting, people will complain that they are too slow. On the other hand, when romantic movies are shown at a faster speed than production, they look quite ridiculous. The key is that people at that time had their own views on what movies should look like.

Today, the sampling rate of 24p determines our own aesthetic view of what movies should look like: tremor and everything else. However, we are in an era of rapid technological development. One day, maybe not too distant future, movies will be made at 60 fps. Our next generation will regard 60 fps movies as aesthetic norms. They will get used to the crystal clear action that can be presented by high-resolution 60 fps shooting (and frame interpolation allows us to see it today). When they look back on the movies made in the old 24 fps format in the 20th and early 20th centuries, they will also think that it is bizarre and interesting that we can tolerate the jitter limitation of the prior art.. When we recall the silent film era with confused nostalgia, it is worth remembering.