Wen | Xiaoxiao
Editor|Xiaoxiao
3D shooting and 3D image presentation technology is the core reason why we experience 3D visual experience in cinemas. To be precise, if you want to achieve such an effect, you only need 3D image rendering technology. However, in order to make the production process simpler and more realistic, we often use 3D image presentation technology.
The 3D film "Avatar" integrates 3D technology and 3D image display technology to the extreme. Without a doubt, "Avatar" is the most successful 3D movie to date. Taking the film "Avatar" as a case, the application of three-dimensional photography technology and three-dimensional image expression technology in film creation was preliminarily discussed.
3D shooting technology
In order to obtain a realistic three-dimensional picture, a three-dimensional real-time camera system is required. It wasn't until Cameron perfected his 3D live-action shooting technology that they began using a simple 3D camera system consisting of two cameras. This photographic method is equivalent to using two cameras instead of our eyes to obtain two pictures, which provides material for the subsequent three-dimensional image rendering system.
However, 3D shooting is not an easy task. Both cameras need to be synchronized when zooming, displacement, etc., but because the machine is large and bulky, it cannot achieve flexibility when shooting, resulting in many difficult lenses cannot be completed.
In fact, Cameron has been using this technique since Titanic. Since then, this technique has been used in 3D movies such as "Very Little Agent" and "Adventures in the Center of the Earth". He has rich experience in 3D live-action shooting, which is also a solid foundation for his use of 3D technology in "Avatar". And under Cameron's guidance, this technique was also greatly improved, and finally shined in "Avatar".
Virtual shooting system refers to the use of a virtual camera to unfold 3D shooting in a virtual CG scene, and convert the captured real scene into a 3D scene in the computer through 3D tracking software and 3D model software. In the virtual 3D scene, by adding a virtual camera, people can change the position and angle of the camera at will, so as to obtain shooting effects that cannot be achieved in the real scene.
Long before the release of "Avatar", people began to experiment with virtual cameras, which was in the 3D film "The Matrix". The only difference is that this technology is not used in 3D, but only to find a better perspective for the director. However, Cameron improved the original virtual reality technology, and used the virtual reality lens to shoot directly into the virtual reality.
In this way, when videographers use 3D virtual technology, they can easily adjust their position and angle to the most suitable level, so that they can present everything they can see in a 3D virtual environment. With this technology, photographers can express their desired images as they wish.
3D image presentation technology
Most of the true three-dimensional look and feel we get in the cinema is based on three-dimensional image rendering technology. There are many techniques for 3D image presentation, and each has its own advantages and disadvantages.
When we watch movies, we must determine which way to choose according to factors such as equipment conditions and data provided by 3D movies. In the case of Avatar, most of the polarized 3D display technology we use in theaters.
This is mainly because: "Avatar" uses a single lens, two lenses, and these two lenses are like two eyes. The data type generated by this 3D photography technology is especially suitable for glasses-type 3D image presentation technology. However, glasses-free 3D display technology has higher requirements for 3D data. In this way, "Avatar" is limited to only 3D image display technology.
Chromatic aberration-type three-dimensional image rendering technology is to distinguish the color difference between the two lenses through the color difference between the two lenses, so as to achieve the purpose of three-dimensional image rendering. First, we post-processed the images captured by both cameras so that they were displayed in red and blue light. Then fuse the two surfaces into one.
When people watch a 3-D movie, the two stereoscopic glasses they wear filter out the colors of the image they want to see, so that one pair sees only red light, and the other pair sees blue and green light. In this way, the viewer's left eye can see the picture obtained from the left camera, and the viewer's right eye can see the picture obtained from the right camera. In this way, the viewer will get an immersive, immersive feeling.
Chromatic 3D image rendering technology has the advantages of low manufacturing cost, simple manufacturing principle, and easy implementation, but its technical shortcomings are also obvious. The three-dimensional image obtained by this method is prone to problems such as uneven color, which makes the visual effect of the three-dimensional image not prominent enough. In addition, such glasses with chromatic aberration are easy to cause visual fatigue, so they are not suitable for long-term viewing.
Polarized 3D image presentation technology requires the viewer to wear polarized glasses to distinguish between two images by refracting the image. It is a kind of stereoscopic glasses composed of two lenses, which use the refracted light of the two lenses to obtain the image you want and achieve three-dimensional visual effects.
First, we display the images taken by the two cameras in the vertical and horizontal directions through the polarization processing of the display, and then combine the two images into one image. When viewers watch 3D movies, the left and right lenses of the polarized stereoscopic glasses they wear will filter out what they don't need to see according to the polarization angle of the light, one can only see the polarized light in the vertical direction, and the other can only see the polarized light in the horizontal direction.
In this way, the viewer's left eye can see the picture obtained from the left camera, and the viewer's right eye can see the picture obtained from the right camera. By putting these two images together, the viewer can see what they see in the movie, which is the three-dimensional picture.
The three-dimensional sense of the picture presented by this 3D image presentation technology is much better than that of the chromatic 3D image presentation technology, and it will not cause the color difference of the picture, and the manufacturing cost of this 3D glasses is relatively low. Great for movie theaters, playgrounds, and other places where there are many people watching. At present, most domestic theaters have adopted this 3D projection technology.
According to the principle of image presentation, naked-eye 3D image presentation technology can be divided into three types: one is pointed light source 3D image presentation technology, and the other is cylindrical lens 3D image presentation technology.
As a new type of three-dimensional technology, point light source three-dimensional image reproduction technology can realize the realism of three-dimensional images, and has the irreplaceable advantages of other three-dimensional image reproduction technologies. This technology has a high resolution, can reproduce the content of the 3D image well, and has a strong sense of stereoscopic, which can bring great 3D visual enjoyment to the audience.
When rendering a 3D image, the content that the left and right eyes need to see will appear on the screen one after another. Its display device has a fast refresh rate, which can make both eyes receive the required image information in a very short time, so as to form a 3D visual effect.
However, the display device of this 3D image rendering technology is composed of two sets of LED displays, and a powerful central processing unit is required to process the presentation of the image, which leads to the high cost of the technology. At present, the technology is not mature, it is still in the research and development stage, the three-dimensional image display is unstable, and its equipment system needs to be further improved.
Cylindrical lens 3D image presentation technology is to refine and deform the image through a convex lens, so as to realize the presentation of 3D images. The display of this technology is generally installed with a cylindrical lens on the LCD screen, and the focal surface of the cylindrical lens is in line with the image surface of the LCD screen.
In the rendering of 3D images, the cylindrical lens in front of the image plane of the LCD screen uses its magnification and refinement to break down each pixel in the image into multiple pixels.
Viewers can watch the movie through a long lens. Because the left and right eyes of the audience are at different angles and positions, they will see that the angle of each pixel in the image is different, so the left and right eyes will see what they want, resulting in a 3D visual feeling.
Cylindrical lens three-dimensional image display technology is a high-definition, high-stereoscopic image display technology, but its disadvantage is: the user's eyes cannot be rotated when viewing three-dimensional images. In addition, the current 3D image presentation technology is not compatible with the production process of LED and LCD, so in order to manufacture a proprietary display device, a lot of money must be invested, which has caused a great obstacle to the popularization of the 3D image presentation technology.
Post-production of 3D visual effects
On the basis of 3D image rendering technology, through the post-processing of high-quality images provided by the 3D photography system, a series of shocking 3D films such as "Avatar" are finally obtained.
Before the use of stunts, the traditional post-production technology was to use the printing method to adjust the overall tone and tone of the film, but the adjustment was very limited, especially for subtle color processing, or partial modifications. In the digital age, the post-production technology of films has more freedom than ever before.
You know, in traditional movies, its exposure characteristic curve is fixed, even if a powerful display is used, its exposure and tone will not exceed this limit. Digital cameras can get different exposures by simply adjusting the camera's capabilities, plus post-processing techniques.
Using 3D technology, you can make the hue of color, like an oil painting, can be adjusted as you like, if you have enough artistic talent, enough imagination, you can create a mysterious light on the screen, a colorful pattern, an abstract, lifelike Chinese painting.
"Avatar" uses a 3D camera system invented by director Cameron, which will produce a 3D image processing data after being used in the real world, so the picture produced by this camera technology can be completed with some professional editing software such as Autodesk Flame, Avid DS, Quantel 4 K and so on.
If a 3D camera is used, each frame corresponds to the left and right eyes of the viewer. The two image archives are synchronized, except that they were taken from different angles.
Therefore, in order to post-process the video generated by the dual-camera dual-lens 3D shooting system, it is necessary to import two video files at the same time in the post-production software, and carry out synchronous editing work on the two video files, including editing, color grading, production post-effects, etc.
If the perfect synchronization cannot be achieved during post-production, it will lead to unrealistic 3D effects, and even lead to serious degradation of 3D effects. But because these two channels are general 2D images, most 2D image processing software can edit them, such as EDIUS, Ocean, Aftereffect, Premiere, and so on.
epilogue
Film is an art, and art is inseparable from the support of science and technology. The use of 3D technology in film has caused a revolution in film, which has been integrated into the production process of film and has made the art of film develop like never before.
We should not only conduct in-depth research on 3D film technology, grasp its development trend, master its development trend, but also dig it deeply, so as to make it an important way and carrier to educate the people, publicize the masses, and carry forward the spirit of the times, so as to maximize its social value.