Technical specifications of IMAX-3D

In order to greatly increase the resolution of the image, IMAX uses a special 70 mm negative. The image size of the traditional 70mm film is 48.5mm× 22. 1mm (Todd-AO), and the image size of the IMAX film is 69.6 mm× 48.5 mm. In order to expose at the speed of 24 frames per second of the standard film, the speed of the IMAX film is three times that of the ordinary film.

There are some technical difficulties in showing a blockbuster-the traditional 70 mm film is not stable enough after being enlarged by 586 times. So IMAX needs some new technologies. William Shaw of IMAX Company adopted an Australian patented technology called "rolling cycle" to screen movies, mainly adding a compressed air device to speed up the film rolling, and placing a cylindrical lens at the front end of the projector to keep a vacuum state during the screening. The IMAX projector is fixed with screws, and the projector is fixed in a completely horizontal state by four screws and gears. A cam control arm is also added to offset the slight shaking in the screening process. The shutter length of the projector is also about 20% longer than that of traditional equipment, and the brightness of the lamp tube is higher. The largest xenon arc lamp 12- 18 kW even needs water-cooled electrodes. Therefore, the cost of IMAX system is not cheap, and the weight reaches 1.8 metric tons.

IMAX is based on Kodak's ESTAR (also known as PET, also known as DuPont's Mylar? ), the reason is not the strength of the substrate, but the size of the substrate will not be affected by the developed chemical liquid. IMAX's film feeding equipment has strict requirements on the side hole or thickness change of the film. IMAX film can be classified as "15/70" film, which means that this 70mm film has 15 side holes per frame. IMAX film is very heavy, and the film reel is much larger than ordinary movies. In order to make full use of the movie area without sound track, IMAX movies use six-channel 35 mm tape to play the sound synchronized with the picture. In the early1990s, the digitized six-channel sound source separated from the picture was changed into a more accurate pulse generator as the synchronous signal source of the traditional SMPTE time code. This is the predecessor of dolby digital, DTS and other cinema multi-channel systems in the future.

With the continuous development of IMAX, new expression techniques appear, such as stereoscopic images, up to 48 frames per second. In terms of sound system, there are Sonic-DDP (direct disc player), stereo sound system and oval speaker group. Stereo version of IMAX technology. In order to create a three-dimensional depth of field, IMAX 3D uses dual cameras and dual projectors for shooting and projection.

Objective IMAX 3D adopts polarized light projection and wears polarized glasses to analyze stereoscopic images. Most IMAX 3D cinemas use linearly polarized lenses. Other companies use circularly polarized glasses, which are less affected by the rotation angle of the glasses, and the effect is basically not affected when the audience tilts their heads, unlike linear polarized glasses, when the audience tilts their heads, there will be a virtual shadow of a three-dimensional picture. In the new IMAX technology, the frame rate is increased from 24 frames per second to 48 frames per second to reduce the flicker problem. Published in 1992 World Expo in Spain. However, it was abandoned in 2000 because the shooting cost was twice as high as usual.

Due to the appearance of digital IMAX in 2008, IMAX HD (48 frames per second) is no longer out of reach. At the end of 20 12, the hobbit: an unexpected journey, the first DMR is a digital IMAX movie with 48 frames per second. The latest IMAX technology released in 2008, the projector supports DLP technology, and the resolution of digital IMAX is 2K, which is the same as that of general digital projection, because its resolution is much lower than that of film IMAX. In order to ensure that the movie screen will not be degraded by enlarging and showing the giant screen, the digital IMAX screen has been reduced a lot, even the screen is only 8.2 meters high (digital IMAX of Dayuan Budweiser Studios in Kaohsiung, Taiwan Province Province), and the original "giant screen and super high quality" of IMAX have been lost.

The advantage of digital IMAX is that it eliminates the shortcomings of heavy 70 mm film and the picture is bright and clean.

IMAX Company is expected to launch a new technology-laser digital IMAX in 20 13, and the projection resolution will be improved to 4K, and the color presentation will be better than the previous digital IMAX. Laser digital IMAX will improve the resolution of digital IMAX in the past, keep the original screen ratio of 1.43: 1 in IMAX, and still play the complete movie picture content when encountering the picture taken by IMAX camera.

Hard-core IMAX fans abroad call IMAX digital cinema LIEMAX, a fake IMAX. Because some viewers are strongly dissatisfied with the picture effect of IMAX Digital, they complain that the picture quality in the front row is unbearable. The picture ratio of IMAX is 1.44: 1, while the picture ratio of digital IMAX is 1.78: 1, so the height of digital IMAX is only 4/5 of the height of film IMAX for the same width screen, so the digital IMAX system can't play a complete IMAX film with 70mm film, and the image will be cut when playing. And the screen area of digital IMAX is usually smaller than that of film IMAX cinema. For example, the screen heights of IMAX Cinema in Dongguan (22m high) and IMAX Cinema in Beijing Film Museum (2 1 m high) are almost twice as high as those of Wuxi World Cinema (0/0.6m high) and Beijing Wanda Cinema Shijingshan Store (0/2.6m high). All kinds of shortcomings make the audience complain that the fare is not worth it and it is not worthy of the title of IMAX.

DLP projectors for projection generally use two DLP projectors with 2k resolution, and the images of the two projectors are superimposed. Compared with the movie version of IMAX, the main advantage is that the brightness is doubled and it is compatible with 3D playback. The advantages of IMAX's large screen and high resolution are lost. The resolution of IMAX Digital is only equivalent to the level of 35mm film copy after being played for many times, while ordinary 35mm film master tapes can mostly reach 4K resolution, while IMAX 15/70mm film has at least 6K- 10K resolution, the theoretical value is 12800x8700 pixels, and the actual value is about 6120x40X. The resolution of IMAX digital projector 2K(2048× 1 152 pixels) is only slightly higher than that of HDTV 1920× 1080 pixels, and even cannot reach the resolution of Sony 4K cinema 4K(4096 x3072).

Most IMAX cinemas in China also adopt IMAX digital broadcasting system. For commercial reasons, they hide many shortcomings of digital IMAX and claim that "IMAX Digital is an upgrade system of IMAX movie version" to confuse consumers. These theaters can emphasize the advantages of digital IMAX in brightness, without mentioning the disadvantages of screen resolution.

Target IMAX is testing two 4K projectors. Because the images of the two 4K projectors are superimposed instead of spliced, the resolution is still 4K. Although it has been greatly improved compared with the 2K projector, it is only a high-brightness Sony 4K cinema at most, which can't reach the definition of 70mm film projection.