Production skills of 3D film and television shooting

Lead: Like ordinary 2D video, 3D stereoscopic video production is divided into pre-production and post-production. Compared with 2D video, they have both similarities and differences. The following are the 3D film and television production techniques I have carefully arranged for you. Welcome to refer to them!

First, comfort.

The first thing to ensure in 3D film production is the comfort of viewing. This kind of comfort simply means no dizziness, no edema, slight or no ghosting as far as possible, reasonable picture access, unified three-dimensional effect of the whole film and so on. The viewing comfort varies from person to person, and different viewers may have different visual reactions. We should take the public's viewing ability as the balance point, rather than conservatively and deliberately emphasizing the three-dimensional sense.

Second, the difference with ordinary 2D

The production of 3D stereo photography is based on the production of 2D movies, but there are still some differences. From a macro point of view, we can't take 3D stereo shooting in the mode of 2D shooting and production. The technical methods are different, and the shooting concept is also different. There must be a trade-off between 2D and 3D. For example, in 3D stereo shooting, we suggest to use zoom as little as possible or even not, and use a sports camera instead of zoom. This method is quite different from the ordinary 2D shooting mode, because it takes into account the consistency of synchronous zoom of dual cameras. As far as the synchronous control system of stereo shooting equipment is concerned, it is still a bit reluctant to achieve the same synchronous zoom. Even the top foreign wireless laser follow-up focusing and synchronous zoom control system can't guarantee complete consistency. For example, in post-production editing, traditional 2D video production can use editing techniques such as fast cutting, such as changing a shot every second; However, this method can't be used in 3D video editing, just connect the foreground and the foreground. If the distant view is close to the scene or the near view is close to the scene, it is impossible for the eyes to adapt to the rapid switching of the lens.

Third, the matching of two computers.

Specifically, it is the collocation of dual-camera lenses. If you think that you can use two cameras or the same type of film machine for stereo shooting, it is impossible to shoot a perfect stereo effect. There are no two identical lenses in the world, that is, no two lenses with identical images. This causes the problem of lens matching between two cameras in the process of 3D stereo shooting. In the shooting picture, especially the four corners, due to lens distortion and other problems, one or some angles will be deformed, which makes it impossible for the two lenses to be completely consistent; Choosing high-end lens, especially focal plane, will reduce this phenomenon, and it is also necessary to adjust the matching through the frame of 3D stereo camera. We use a special calibration chart when matching two computers, through which we can quickly and intuitively complete the matching of two computers.

Four, synchronous control system

Three-dimensional shooting uses two machines, and synchronous control is particularly important. The current synchronous control system mainly has the following functions:

1, synchronous recording. This function realizes synchronous recording and pause between two computers.

2. Change synchronously and focus. This function realizes dual-machine synchronous zoom focusing. The difference between function and price can be divided into four categories. One is lens circuit control. This control system connects the lens through the data interface, transmits the logic control instruction, and realizes the zoom of the lens. Suitable for Canon and Fuji lenses. The first is lens mechanical servo control. This kind of servo motor is attached to the lens adjusting ring. Zoom and focus use one set of motor respectively, which is suitable for all lenses, including focal plane. There is also a wireless laser control, which belongs to the highest-end control system at present. It can also be said that it was specially developed for 3D stereo shooting. Four channels and eight motors, wireless control, laser following and focusing, technology first, the best synchronization effect, but the highest price. The last category is the supporting control system produced by camera and film machine manufacturers, such as the stereo lens and synchronous control unit of redone and arri film machines; This control system can be perfectly integrated with shooting equipment, but the disadvantage is that it is highly specific to the model and expensive.

Fifth, the importance of 3D stereo shooting equipment.

The 3D stereoscopic shooting devices referred to here are 3D stereoscopic devices such as stereoscopic shooting stands and on-site monitors. At present, there are two kinds of stereo shooting stands: vertical and horizontal. Due to the size of the left and right parallel stereo camera frames, the distance between the two cameras (hereinafter referred to as the machine distance) cannot be very small, so the distance between the two lenses is difficult to reach the optimal distance of about 6cm, so there will be discomfort such as ghosting and eye edema when shooting close-ups, so the parallel stereo camera frame is not suitable for shooting close-ups. Take Sony ex 1 as an example, it is basically not suitable within 3 meters. There is no machine distance problem in the structure of vertical stereo camera frame. The two lenses can completely overlap, and the golden distance of 6cm is no problem. Of course, the shooting prospect is no problem. Vertical stereo shooting stand is a common shooting stand at present, and the shooting effect is also the best at present. The only drawback is that the vertical shooting picture must use a spectroscope, and the quality of the spectroscope is different from the imaging effect, which will theoretically affect the quality of the shooting picture; Extremely critical photographers may be more repulsive, but we believe that eyes are the best inspection tool, so why do we have to use data to judge the loss of pictures that glasses can't see? Moreover, the current stereo shooting technology and equipment can only do so.

The 3D stereo camera frame should have multiple adjustment functions. Adjustment is divided into two categories, one is the adjustment of the distance and angle between the two machines (hereinafter referred to as angle); The other is the adjustment of matching between two computers. The adjustment of the matching between the two cameras is mainly the adjustment of the four-axis angle of XYZR. Through the adjustment of these angles, the matching degree of the lenses of the two cameras is improved. To put it simply, the height, level, tilt and rotation of the two shooting machines are optimally matched to ensure the stereoscopic effect of the shooting picture. There are only horizontal staggered differences between the two pictures taken in 3D stereoscopic photography, but the vertical and tilt should be the same. The adjustment of the angle between two computers is used to control the positive and negative parallax, which is often called entering and leaving the screen. The angle between two cameras needs to be adjusted in real time according to different shooting scenes, which is the most important link and technology for shooting 3D stereo.

Stereo display is an important shooting equipment. Some photographers use ordinary double screens and screen displays to monitor the stereoscopic effect, while others just shoot blindly. These practices can be said to be unscientific and irresponsible, not to mention shooting blindly. It is estimated that nine times out of ten the shooting materials can't be used unless the photographer is experienced and skilled. Using the screen viewer as a monitor, the stereoscopic effect of the shooting scene can only be determined by watching the stereoscopic effect. In this case, personal subjective visual factors play a decisive role and are unscientific. We always pay attention to science and rationality when taking 3D stereo photography. The stereoscopic display we use is polarized liquid crystal, which has the functions of main channel, sub-channel, phase difference and stereoscopic synthesis. These accurate display data provide important technical support for three-dimensional photography.

Six, positive and negative parallax

The above is the positive and negative parallax, which is often referred to as the access screen. As we all know, 3D stereo is shot by two machines, and there is a certain relationship between the two machines. Machine distance is to control the overlapping range of two pictures, that is, the strength of three-dimensional sense; The included angle is the intersection of the shooting angles of the two cameras after the light is extended. This intersection is called the viewpoint, and the end of the viewpoint near the lens is called the difference of the front view, and vice versa. The difference in elevation indicates the stereoscopic effect of the screen, and the negative parallax indicates the depth effect. In 3D stereo shooting, the parallax of each scene is different, so it is necessary to determine which effect to use according to the shooting scene and theme. The relationship between camera distance and included angle is complementary, that is to say, they should be adjusted at the same time. The specific principle and adjustment method can only be understood and summarized in actual shooting, and relevant experience can be accumulated.

Seven, stereo imaging principle

Stereoscopic imaging is because the left and right eyes see two different pictures, which are synthesized by the brain and present a stereoscopic effect. And 3D stereo photography is the principle of simulating binocular vision imaging. Besides the principle of binocular vision, it is the layout structure of the picture; A picture with obvious layering can show a good stereoscopic effect. Simply put, the photos taken must have a foreground and background, which is the basic requirement. Generally speaking, the reasonable three-dimensional layout is foreground, middle scene and background; Too many layers are unnecessary, but it will make the picture messy and affect the three-dimensional effect. For example, a group of people shoot from the front in front of a green background; If people stand in a row sideways, there is basically no three-dimensional sense, because the level of people and background is not obvious. Although there is physical space, this space and level is equivalent to shooting ordinary 2D for 3D shooting, and the finished picture is difficult to be calculated by the brain. On the other hand, if the figure stands in the shape of a "pin" or a line is vertical, the stereoscopic effect is very obvious, because the way the figure stands forms an obvious hierarchy, which is very suitable for 3D stereoscopic expression.

People's eyes have complex structures and super functions. To some extent, 3D stereo shooting based on binocular vision principle can only be said to simulate the function of eyes as much as possible, but it can never be surpassed. In this case, it is necessary to treat the flaws in 3D stereo shooting rationally, and these flaws are not the problems of technology and equipment, but the basic laws that people see things, or the unbreakable laws of nature. For example, the common ghosting phenomenon in 3D shooting is that some pictures or some elements in the pictures have slight ghosting when watching with glasses. Most of the ghosting phenomena are caused by inaccurate shooting, but some ghosting phenomena are inevitable. Please do an experiment together:

Please put your index finger upright between your eyes, with the height of your fingertips equal to your eyebrows, and move forward 10cm from the tip of your nose, then look at the distant scenery. If you focus on the distant scenery, you will see two index fingers in the corner of your eye; On the other hand, if you focus on your index finger, there are two groups of scenery in the distance, which are ghosts. The farther away from the index finger, the bigger the scene ghost, the closer to the index finger, the smaller the ghost, and there is no ghost attached to the index finger.

Please complete this experiment and summarize the reasons yourself, so as to extend your understanding of 3D stereo shooting. People's eyes see things like this, so it is impossible to break through this rule in 3D stereo shooting. In 3D stereo shooting, we suggest to minimize the distance between the subject and the background, adjust the camera distance to the best position, and make the positive and negative parallax have a better balance, which is an effective method to reduce ghosting. However, in some scenes, due to the constraints of the actual situation such as the shape of the object and the overall environment, no matter how to adjust it, it is impossible to avoid ghosting. Let's design a shooting scene to illustrate: the shooting scene is the airport, the whole is empty and the picture is refreshing. The shooting subject is an airplane, which is shot at 45 degrees in front of the nose, reflecting the three-dimensional effect that the airplane is slender in depth and the nose comes out of the screen, but there is a lamppost in the background of the airplane. As far as this picture is concerned, the visual point needs to be placed in the middle section of the aircraft fuselage, that is, on the wing, so that the positive and negative parallax can perfectly show the overall depth and nose sense of the aircraft, and the three-dimensional effect of the picture is perfect. The farther the visual point is in the wing, tail and light pole in the background, the greater the crossing range. In this way, the overall stereo effect of the plane is perfect, but the light poles in the background have ghosts. This is because the plane is huge and the lamppost is relatively small. The increase or decrease of the distance and included angle by several degrees has little influence on the plane, but it has great influence on the lamppost in the distance. However, the cross amplitude of positive and negative parallax is fixed, and it is impossible to produce different changes with the different volume ratio of the subject.

Eight, a correct view of the three-dimensional effect

I found a problem in my contact with customers and peers, that is, I like to compare with Avatar. The three-dimensional version of Avatar works perfectly, with no ghosting. To be exact, the production of Avatar, most of the scenes are made of three-dimensional effects, especially perspective, which is integrated with the main characters of the real shot with a reasonable overlapping range, so that the overall picture looks perfect and there is no ghost. In other words, if the scene of Avatar can be filmed and actually filmed in 3D, there are still ghosts. The shooting and production technology of Avatar, whether known or unknown, has given us great learning value. The value provided to us is how to look at and explore 3D stereoscopic technology, rather than comparing equipment technology. Avatar is a masterpiece that brings together the world's top film and television production technologies, costing hundreds of millions of dollars and lasting for many years. Only by this, no one can compare at present. But no matter how advanced the technology is, it can't go beyond the limits of physics and nature, and it can't override the resolution of human eyes and brains. Scientific 3D concept and technical means to improve stereoscopic effect are the basic principles of 3D film production and shooting. You can't imagine why out of thin air, nor can you demand the effect out of thin air. To put it bluntly, the effect of any kind of movie, whether 3D or 2D, is directly proportional to the budget. It is absolutely impossible to achieve the effect of Avatar by shooting a 3D video with a budget of hundreds of thousands or hundreds of thousands.