Comprehensive awareness of 3D video – from technical concept to monitoring and measurement

There are two very important trends in the development of TV: from standard definition to high definition, the resolution will be higher and higher; 3D technology to achieve stereoscopic vision. In particular, 3D technology is an important trend in the development of TV technology for a long time in the future.

3D, if shot and made well, looks and feels very good, with a strong presence and a very impactful picture. Some 3D movies are realized through post-production. If the production is not good, it is not as good as 2D movies, because the software converts 2D into 3D. If the quality is not guaranteed, the effect is not necessarily better than 2D from a viewing point of view. . Therefore, some technical means must be used to ensure that the 3D stereoscopic content produced is very suitable for the sensory experience.

How does the human eye perceive 3D?
A very important effect of 3D is the stereoscopic effect, because the parallax between the left and right eyes produces the so-called 3D effect. The parallax has a certain range. If the parallax exceeds the range, it will produce a very bad visual experience, and even watch 3D movies for a long time. Dizziness or discomfort. When shooting and post-production 3D movies and TV, if you don’t grasp the parallax or depth of field, you will have a similar uncomfortable experience. Of course, there is no good evidence that watching 3D will hurt, but there will be discomfort.

The most traditional 3D glasses to see the 3D effect, if you do not wear glasses, it will produce a very virtual picture, cyan is in front of red, or red is in front of cyan, red represents the picture seen by the left eye, and blue represents the right eye. to the screen. It is precisely because they have a certain level of disparity and parallax that leads to the feeling of 3D. If the 3D picture is not done well, it will give people a very poor feeling. The 3D that everyone sees in the cinema is not seen with red and blue glasses. The TV at home will have active 3D glasses. Through interlaced scanning, the first scene transmits the picture of the left eye, and the second scene transmits the picture of the right eye. When the left eye comes, it is equivalent to closing the right eye. Everyone You will get the picture of the left eye, when the right eye comes, the left eye will be closed, and the image of the left eye and the right eye can be obtained through the active glasses, and finally the feeling of 3D in the mind, there are more 3D on the market now. television. In the movie theater, the left eye transmits the video picture to everyone through the horizontal and the right eye vertically. No matter which way, there are basically two pictures of the left eye and the right eye. A certain gap, the distance between the left eye and the right eye is between 60-65 mm.

Comprehensive awareness of 3D video – from technical concept to monitoring and measurement
Figure 1: Naked eye 3D effect.

There is a certain gap between the two pictures seen by the left eye and the right eye. Human eyes analyze the picture, and through the judgment of the human retina, the signals obtained by the left and right eyes are analyzed by the brain to form a three-dimensional feeling, and the relationship between their positions is analyzed. The relationship with the three-dimensional, the final result is the 3D effect, which is the process by which the human eye perceives 3D through the senses. It turned out that someone asked a question, if you close one eye, can you feel the 3D effect? In fact, the depth of the image needs to be perceived by two eyes, and sometimes its stereo information can be perceived through one eye. This information will reveal the distance through 2D, and it will provide us with some information, the image is revealed and masked part, through which to judge who is in front and who is behind. When watching 3D movies, there is often the effect of the image running behind the screen. There are several scenes in “Rio Adventure”. When the parrot learns to fly, it will rush towards you. This effect is not often seen. Made specially. Beijing TV has done some 3D experiments and gained some experience. It is easier to accept the image when it goes to the screen. If the effect of going out is not very acceptable, everyone should also consider that the impact of the outside image has a certain degree when doing 3D effect. ratio, i.e. can’t do too much.

Some information can perceive its three-dimensional depth with a single eye, and we can see the 3D effect through changes in light and shade, including changes in texture. For example, if you look at a flower from a distance, you can see it as one piece, and if you look at a close-up view, you will be able to distinguish it clearly. The farther away, the smaller the picture will be. Through this information, you can perceive the depth of 2D. We can also perceive the depth of 2D by judging the size of the object or changing the size of the object. Motion parallax, when sitting in a car, near objects are facing away from us, these can perceive depth through one eye. The position of the object seen through the two eyes is different. This can only be felt through the two eyes. Through these, the three-dimensional distance and depth can be well perceived.

3D video shooting
How to restore to what people can see? Through two cameras, what was previously seen through one camera is two-dimensional, and two cameras simulate human eyes, taking pictures of the left and right eyes. At present, the two cameras are arranged in two ways, one is horizontal side by side, and the other is vertical up and down. You can do some experiments according to different systems. Which one is better, the distance between them is generally similar to the pupil of the human eye, 60-65 mm. When shooting, the distance between the two cameras can be adjusted according to the close-up or long-range view. It is very important to ensure that the aperture, focal length and brightness between the two cameras are consistent, otherwise the two pictures taken will look a lot of discomfort to the human eye. Of course many cameras are now mechanically self-adjusting via cables, but it is difficult to guarantee that the two are exactly the same. There are some studies now, such as how much the displacement difference between the two cameras is acceptable and how much the brightness difference is allowable. This is also the standard and main content of 3D test measurement in the future, as well as the vertical difference between the eyes and the difference in brightness. How many people’s feelings will not be so obvious. Another problem is that the moving object needs to be confirmed with the left eye and the right eye when shooting. If the moving object is shot without the left eye or the right eye, the object will look strange when it is composited and cannot be superimposed. In general, the background can be different between the left and right eyes, but the moving objects must fall within the area captured by the left and right cameras.

The other is the vertical camera placement. The 3D left eye signal directly enters the camera, and the right eye is divided by the beam splitter. When it is divided, the image is inverted. It needs to be turned over by the rotation circuit, because the processing between the circuits It is not the same. Make sure that the time of the images taken is the same. If the time is one or two frames apart, the final picture will be completely messed up. There was an article that explained why it should be vertical, because horizontally because the size of the two machines themselves is too large, it is difficult to ensure that the distance between them is 60-65mm, because the machine is relatively wide, it can be well done in a vertical way to adjust the spacing between the left and right cameras.

There will be a problem with the angle of the camera both horizontally and vertically. Should it be done in parallel or in a diffused way? Parallelism can ensure the horizontal direction very well, but there is a problem: people generally have a convergence point when looking at things. If you shoot in parallel in the early stage, you can converge in the post-production, and adjust the pictures between them. It will be more difficult to converge, and you have to count the shots The distance between the position of the camera and the camera needs to be positioned to whether the screen is facing out of the screen or inward. There will be a lot of calculations inside, which is more troublesome.

The so-called 3D is the left and right displacement caused by parallax, and finally the 3D effect will come out. There are four kinds of parallax (see the figure below): zero parallax, the left and right eyes see the same distance; positive parallax is when the right eye is in front of the left eye, and the general picture is behind the screen; negative parallax is when the right eye sees the picture on the left On the left side of the eye, the picture seen with negative parallax should be in front of the screen; the normal eyes cannot have scattered vision, and it is necessary to avoid scattered parallax when shooting. Zero parallax is generally a movie or TV screen. Which one is the screen? The point of zero parallax is the movie screen and the TV screen. If the picture is going to go out of the screen, it can be used as a reference, and it can also be used as a reference when entering the screen. Positive parallax means that the right eye is on the right side of the left eye, its point is behind the screen, and the effect of the picture is at the back of the screen. The negative parallax picture is in front of the screen defined by zero parallax, the picture viewed by the right eye is to the left of the left eye, and the objects are all outside the screen, which will create a feeling of being suspended and fly towards the visual direction. Dispersed parallax human eyes will not spread out, and there will be no such picture if you actually shoot.

Comprehensive awareness of 3D video – from technical concept to monitoring and measurement

Figure 2: Four different types of parallax effects.

When shooting, there will be a plane axis. We recommend the so-called negative parallax not to lean too much on the eyes when flying towards the eyes. If a bullet suddenly hits, if it hits too close, it will not adapt to the human eye very well. Where is the best location for the screen? Some studies say that the position of the arm length is a more suitable negative parallax, but it is not possible to gather a lot of points in order to pursue the effect, so the effect is not necessarily good, and the scattered places do not need to be too large. There is no standard definition of what range we can accept. There will be many experiments, including data.

Because it is shot by two cameras, it is necessary to ensure that the brightness and chromaticity between them are consistent. If there is a certain difference, it will look uncomfortable. When viewing, we need to superimpose the left eye and the right eye. How much vertical chromatic aberration, brightness and chromaticity difference can we allow? Although we have a lot of software and tools to ensure the aperture and focus between the two cameras, it is impossible to guarantee complete consistency, and there is currently no authoritative standard to define what range is acceptable. If the left eye is not completely separated from the right eye, that is, although it is the information of the left eye, it can also see the things of the right eye, which will cause a very chaotic effect to our vision and will produce a very uncomfortable feeling.

Set a screen with zero parallax. If the parallax screen is always converted when shooting, it will have a great impact on us. It is not recommended that you change the zero parallax. The screen with zero parallax in the same scene should be fixed, and the same product cannot be changed. The eyes must constantly adjust the focal length and focus, and the eyes will be very tired. If it changes, it is recommended to use 2D when transitioning from one screen to another, and then create a three-dimensional feeling on the other screen, so that human eyes will have the process of adaptation, and it will not look like Especially uncomfortable, do not change the zero parallax screen in the same type of scene.

3D video monitoring and measurement
Tektronix also has some related solutions for the test of brightness, chromaticity and focal length shot in 3D. If the brightness of the left and right pictures is very different, the 3D effect will be very bad for everyone. Using the checkerboard test method, you can easily see how much the brightness of the picture is different between the left and right eyes. If the brightness and chromaticity are not very different, there will not be a big transition between the left and right, and the brightness and chromaticity will appear to be compared. Smooth feeling, by adjusting the aperture and lighting, to ensure that the brightness and chromaticity are within the same range. The following picture is a schematic diagram of the image error of the left and right eyes. The right side is due to parallax. The sunlight penetrates in. If the two pictures are combined into a 3D effect, it will look awkward. If the 2D shooting is not allowed, the 3D shooting should also be avoided With this effect, there is no sun on the left and there is a sun on the right, so there will be very big problems in synthesizing the picture. It can be seen from the test waveform that the brightness of the right eye is obviously higher than that of the left eye, and the aperture should be adjusted to avoid halo.

Comprehensive awareness of 3D video – from technical concept to monitoring and measurement
Figure 3: Image error for left and right eye: different brightness levels, different colors.

Comprehensive awareness of 3D video – from technical concept to monitoring and measurement
Figure 4: Video level adjustment with the Tektronix WFM8300.

The two lenses should be adjusted at the same time. If the focal length or aperture between them is different, the picture will be very bad. The effect of subtracting the right eye from the left eye will have a certain difference. This is correct, we hope to see There is a difference between the left eye and the right eye, and there is a certain difference in the horizontal displacement. In the picture inside, the distance between the sea and the sky in the distance is not three-dimensional. Here we have a difference, it looks like A more ideal three-dimensional feeling. If the wheelbase is not adjusted properly, the left side will be larger than the right side. The difference between them is not only horizontal, but also vertical displacement difference, which is not allowed, so adjust the aperture, make sure to focus, and ensure that there is no vertical difference between them.

The oscilloscope can superimpose the left and right eyes, mark the color of the right eye or the left eye, and directly put on the glasses to see its effect. This kind of glasses can be marked with red and cyan or green and magenta, so that the picture can be easily judged If you want to know the depth of the stereo, such as how many pixels there are, you can put a grid of visual difference here, each of which is 129 pixels, the displacement difference represents the depth of the stereo, and the vertical aspect can be 50%, 25% or 10 %. There is another way between the left and right eyes is the cursor, directly mark the cursor, the bottom of the Display screen will directly tell you how much the target horizontal parallax is, about how many pixels, this way you can see whether the left eye is in front or the right eye In the front, whether the picture is out of the screen or in, and what is the stereo depth.

3D shooting in the end how to transmit? There are several ways at present, one is SDI transmission, both of which are high-definition, and 3G will be used in the future. 1080 50p is just one way in 3G. Using two channels of transmission will encounter the problem of transmission delay and disputes. The current method is to use two SDI methods, one is the signal of the left eye and the other is the signal of the right eye, and two test signals will be output. After the system and detection equipment are built, the entire channel is detected through the signals of the left and right eyes. It is necessary to pay attention to whether the signals of the left and right eyes are mixed up, including whether there is a delay between the channels. If there is a delay between the channels, it will cause dislocation, and the 3D effect will have a big problem.

The corresponding test instrument for 3D video transmission is the latest waveform monitor – WFM8300, which can watch two signals at the same time. Through the waveform, it can be judged whether the picture of the left eye is on the right or the picture of the right eye is on the right, so that you can stereoscopically feel whether it is inward or outward. You can combine two signals into one signal, and you can actually see it in the transmission. If you can connect to the projection or channel, you can monitor it. This is the detection of 3D signals.

Comprehensive awareness of 3D video – from technical concept to monitoring and measurement
Figure 5: A waveform monitor that can monitor two signals at the same time – WFM8300.

Not long ago, there was a transmission specification in the US laboratory. There are two ways to transmit 3D signals. One is to transmit 3D left and right eyes side by side through compression. This method is suitable for 1080i interlaced scanning format, the left eye is compressed by half in the horizontal direction, and the right eye is compressed by half in the horizontal direction. The signals are decoded separately, the level is only half at this time, and then up-converted, the obtained picture is 1080i, which is the signal of the left and right eyes. The 720p mode is up and down, the upper part is for the left eye, and the lower part is for the right eye, so the picture is still 720p. The existing system can also transmit the signals of the left and right eyes, and define how many lines to how many lines are for the left eye and how many. How many lines are the right eye, the receiving decoder can also decode the left and right eyes, and Display it through the TV.

Figure 6: Stereo view measurement – edge detection.

The Tektronix video quality analyzer VQS1000 can be used to monitor the transmitted 3D signal, and the edge between the left eye and the right eye can be seen to distinguish who is on the right and who is on the left. Green represents the right eye, blue represents the left eye, if the right eye is on the right side of the left eye, it means that the picture is outward, and there are more detailed ones, which can tell you which pictures belong to the reference, zero parallax, and which picture positions Is the positive parallax, inside the screen, which is the negative parallax out of the screen. Of course, a percentage will be given – roughly how many pixels are out of the screen, how much is the stereo depth, how many are in the screen, how much depth. In this way, you can judge the finished file or actually transmit the stereoscopic effect of 3D video, from shooting to production to transmission monitoring.
Summary of this article
3D is a relatively new technology after all, and everyone is in the process of exploring. Therefore, how to use tools to create 3D images, and how to ensure that the depth of 3D is more appropriate, these issues may require everyone to explore through tools. As the world’s leading provider of test and measurement solutions, Tektronix hopes to cooperate with you in addition to providing leading test equipment and technologies. If you have any test and measurement related information, please give us feedback, including how to do a good job of 3D pictures, let us We work together to promote the development and application of 3D technology.

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