Cinematography

V

Sound Recording

When precise synchronization between sound and picture is required, such as in dialogue scenes, where precise matching of the sound and lip movements is necessary, silent, or “blimped”, cameras are used and the sound recorded directly when filming. Sound recording is usually done on digital audio tape (DAT) recorders, normally in stereo. Synchronizing information is also recorded, usually in the form of time coding, so that sound can be matched to the corresponding images. Many film-makers still use clapper boards at the start or end of each take, as this speeds up the synchronizing of the picture and sound rushes for viewing, compared with lining up time codes on a special reader.

If these recordings are not of sufficient quality, for example, due to intrusive background noise on location shoots, they can be re-recorded later in dubbing studios, where the actor views short sections or loops of the picture, running continuously, with their original location recording on earphones. After repeating the lines several times in sync with the picture and earphone sound, they can then re-record the dialogue, not only accurately lip-synced, but also closely matching the tone of voice, inflexions, and emotional performance of the live acting.

VI

Digital Editing

Nearly all films are now edited using techniques referred to as non-linear editing. The original negative is transferred on a telecine machine to high-quality video cassette, analogue or digital, and the images transferred to mass storage, in dedicated editing machines. The computer has several monitors and uses split screens to present the editor with all the shots for a given sequence, performance, and so on, and a graphic representation of the succession of shots and sound. Alternative cuts can be tried out and as little as one frame added or cut out until the editor is satisfied that the decisions have been made. The results can be reviewed frequently with the director and changes made extremely quickly. The coding system ensures that images and synchronous sound remain accurately matched and edited.

When the final form of the film has been decided, the computer produces a detailed list of the sections of film used, called the edit decision list (EDL). A specialist technician will then work through the list, and cut the picture negative to comply with the EDL. At this stage negatives of shots with special effects added are incorporated. These may include computer-generated images (CGI) produced by highly specialized equipment and technicians.

The computer also produces digital versions of the separately laid soundtracks. Any soundtracks in addition to the synchronous dialogue, such as sound effects, music, or commentary are recorded separately and their placing and combination decided upon and laid. The editor may carry out experimental sound mixes but it is usual for a formal sound mixing session, often called the dubbing session, to take place in a sound studio using the skill of a specialist “mixing” technician. In most cases the soundtrack is transferred to an optical negative, using a machine called a sound camera, to produce an optical soundtrack. The picture and sound negatives can then be printed onto the same film to produce a master “married” positive. This is printed again to a special type of positive film, from which duplicates of the negative are struck to produce the many hundreds of prints of a film required for a major release.

This strategy for the production of feature films is the virtual equivalent of the original scheme, only the form of execution of the editing decisions is digital. An alternative strategy carries the digital phase much further.

A

On-Line Editing

In this case, the digital phase is carried right through to the penultimate stage of post-production. From the edit decision list, each section of original negative is separated out, with a few frames extra before and after the decision points, and has short lengths of spacing film or leaders and trailers, called handles, attached at both ends. In each case the leader has a start mark, from which the selected frames to be used are counted. The section is then scanned to a very high resolution by a laser scanning device, which uses blue, green, and red lasers to digitize the selected material. This pre-selection ensures that only the used sections of the negative are expensively scanned. Each section is coded with a consecutive identifying time code. Sometimes, a video copy is also made, with the numbers from the edge of the negative, called key numbers, inserted in the picture so that the assembly of the sections can be checked for accuracy.

The data of each section of negative is then imported into a non-linear computer and the segments are “stitched” together. At this stage, the colour and exposure grading of the production is carried out. On-line editors have taken over much of the function of the laboratory grader and are sometimes referred to as “colourists”. A number of effects can also be included, such as a fog filter. More complex effects (CGI) are produced by sending the selected digital data to separate facilities where the special effect, such as a light sabre, is added. The new digital data segment is then returned and assembled into the final version.

The graded and assembled digital data of the film is transferred to special ultra-fine grain film negative using a machine with red, green, and blue lasers at very high resolution. These machines record digital images to film at a rate from about 3.2 to 6.5 seconds per frame, so that one second of film action takes from 1 min 17 sec to 2 min 36 sec to transfer. One manufacturer claims to be able to record an entire feature film of 90 minutes duration in a week. From this negative, film prints for distribution to cinemas are made.

An alternative to the production of film prints is to carry digital techniques to the cinema screen directly using digital projectors. (See Digital Projection, below.)

VII

Film Projection

A film projector has a gate, analogous to that in the camera, but in this case there are apertures both in front of and behind the film. Each frame is intensely illuminated from behind by a powerful light source, such as a sealed xenon arc. A lens focuses an image of each frame onto the screen in the auditorium. The film is pulled through the gate in steps by means of an intermittent sprocket, situated just below the gate. Unlike the camera shutter, the projector shutter has two blades and each frame is shown twice. This decreases the dark periods so that they are less noticeable to the dark-adapted eyes of the cinema audience.

An accurately focused beam of light, in the form of a narrow slit, is shone on the optical soundtrack running down the length of the film, to one side of the pictures. The track modulates the beam, varying the light that falls onto a photoelectric device, which converts the variations of the light into electronic signals. These are amplified and reproduced over the loudspeakers. The soundtracks may use a complex digital coding system to reproduce stereo and surround sound in the cinema, as well as to reduce the effects of electronic noise. Techniques for showing films with fully digital soundtracks are still not yet completely standardized and are likely to evolve.

Films are shown in cinemas on screens with different aspect ratios. Originally, the width and height of the screen were in a ratio of 1.33:1 (4:3). Most films are now shown with the top and bottom of the frame masked, so the ratio is 1.85:1—a system referred to as “wide-screen”. In a technique known as Super 35, it is masked down to a ratio of 1.35:1. Some films are photographed using anamorphic lenses, which “squeeze” the image horizontally. This makes them appear vertically elongated because their width is halved, relative to their height. It also means that a wider view is squeezed into each frame. These films are projected through corresponding lenses, which “stretch” the image horizontally to restore their proportions. The whole picture is therefore much wider and is shown on screens that are 2.35:1. Such films are usually referred to as “scope”, the earliest commercial version being CinemaScope^TM.

A few specially equipped cinemas can show 70-mm prints, running horizontally through the projector, using the very large images on the film for projection onto a giant screen. A special “rolling loop” system is employed to avoid the use of film claws and each frame is held flat, in an accurate position, by being pulled onto a glass plate by means of an air-suction system. Multiple soundtracks are used, in combination with the large pictures, to produce a spectacular show. Imax and Omnimax cinemas use these techniques.

Since the frame rate of standard cinema projection is 24 frames per second, motion will only be reproduced at a natural speed if the camera is run at the same speed. If the camera is run at higher speeds, the projector will slow the action down, producing the slow-motion effect. For example, if the camera is run at 48 frames per second, the projection will last twice as long and the action will be slowed down to half its natural speed.

Slower camera speeds will produce the opposite effect, speeding up the action. Time-lapse cinematography is achieved by using special motor and shutter systems on the camera, which can take frames one at a time. In this way a series of frames, taken over a very long time, is projected at a much higher rate, speeding up the action hundreds, or even thousands, of times. This technique is commonly used to reveal very slow movements, such as that of growing plants, or the emergence of a butterfly from its cocoon.

A

Digital Projection

Except for the use of powerful lasers, the public use of which raises safety issues, the problems of illuminating a large screen with a digital image at sufficient intensity arises out of the difficulty of deflecting beams of light and controlling their intensity, which cannot be done using electrical or magnetic fields. A further problem is that the “look” of film projection arises mainly from the fact that all parts of the image of a frame of film are projected simultaneously and not scanned from side to side and top to bottom sequentially, as is the case with video.

However, the development of a new technology, known as digital light processing^TM (DLP), developed by the then Central Research Laboratories at Texas Instruments, has provided a method for the simultaneous projection of large numbers of pixels of light and the very high speed modulation of their intensity. This technique is based on the production of arrays of tiny mirrors, each of which can be deflected by a digital signal. The array, a digital micromirror device^TM (DMD), is constructed on the upper surface of a conventional CMOS static random access memory (SRAM) chip and consists of an array of 1,024 x 1,280, that is 1.3 million, aluminium micro-mirrors, each carried on a diagonal torsion hinge. Each mirror is 17 microns (17ìm) square, about a quarter of the diameter of human hair, and can tilt through an angle of +/- 10°, making a total movement of 20°. The close tiling of the square mirrors ensures that approximately 94 per cent of the area of the chip face consists of mirrors, making the total reflection very efficient and even. A system of electrostatic bias ensures that the mirrors are bi-stable, that is they can be “nudged” from one position to the other at high frequencies. The special version of the use of DMD devices for cinema presentation is referred to as DLP cinema^TM.

The digital data of a single frame used by the projector contains the information of red, green, and blue light to be projected to each point on the screen. The light from the xenon arc is split, by means of a dichroic colour splitting prism, into three primary colour beams, blue, green, and red respectively. Each beam shines on a separate DMD, which is used to modulate the amount of that colour in each pixel on the screen. After modulation, the three images are recombined for projection of the colour image to the cinema screen by the same dichroic prism that did the splitting.

The apparent intensity of light for each pixel is modulated by oscillating the relevant mirror. If it is held continuously in the “on” position the maximum intensity of light is reflected from the mirror through the lens to the screen. To reduce the brightness to the eye the mirror oscillates so that the apparent intensity is controlled by the ratio of the time during which it is in the “on” position and that during which it is in the “off” position. If it is held continuously in the “off” position the resulting brightness of the pixel is very low, producing a ratio of about 1,000:1 between the lightest and darkest parts of the image. This form of modulation is referred to as binary pulse width modulation and requires each mirror to oscillate up to thousands of times per second.

For each mirror, the intensity of the appropriate colour is controlled by a 15-bit “word” which is stored in the SRAM. When applied to the DMD each bit is loaded to all 1.3 million mirrors simultaneously and then the next bit and so on for 15 bits. The bits are loaded in bit weight order, that is the most significant bit (MSB) is loaded first and, if it is “on”, the mirror will be turned “on” for half of the available frame time (y x = sec). If the next most significant bit (MSB-1) is “on” the mirror will be “on” for the next one quarter of the frame time. If the MSB-2 is “on” the mirror will be “on” for the next one eighth of the frame time, and so on for 15 bits. Fifteen-bit resolution means that each mirror can produce 32,000 apparent intensity levels for each primary colour for each pixel on the screen. While the image is being projected the system is loading the data for the next frame, ready to download the next “word” sequentially, bit by bit, via the SRAM.

Unlike a film projector, the shutter of which cuts off the light from the screen while the next frame of film is being pulled down into the gate, the DMD reflects the image for virtually all the time and the substitution of the next image is almost instantaneous, making the picture virtually flicker-free. This also provides the most efficient use of the light, so that the projector can produce a picture that appears as bright as that from a film projector, even on large cinema screens. The simultaneous change of the entire projected image maintains the film “look” for cinema presentations.

The high-intensity of light from a powerful xenon arc is filtered by an infra-red mirror to divert heat from the DMDs. In addition, though much of the DMD consists of mirrors and is therefore not liable to overheat, it is water cooled as a safety precaution. The deflected light is reflected into a black “light-dump” and is converted into heat, which is dissipated by a cooling fan.

An alternative method of digital projection, used in prototype versions of the Kodak Digital Projector, developed by JVC, and known as digital direct drive image light amplifier (D-ILA) relies not on the tilting of mirrors but uses flat surfaces whose reflectance is electronically modulated by liquid crystal. In this case the array of pixels is 2,048 x 1,536, giving a total of over three million reflection cells.

Digital projection has many advantages. The cost of the production of hundreds of bulky film prints and their distribution to cinemas is very high. Distribution of digital data is much simpler and more efficient, offering large financial savings. Films may be distributed as specialized DVDs, as digital tapes, or on portable hard disc arrays. Alternatively, they could be transmitted to cinemas on high-speed optical fibre or satellite links. In multiplex cinemas the scheduling could be altered at short notice to change the number of screens showing the film.

The overwhelming advantage of digital projection is that every single show will be technically identical. The problems of damage to film prints caused by wear and tear and mishandling will be solved. The quality of release prints can vary and the dyes can change, causing variations in the appearance of film. With digital projection, the images shown at the local multiplex will be of the same high quality as those at the prestigious charity premieres in first-run cinemas.

However, these advantages inevitably raise issues for the film industry about data security and so encryption and other techniques to prevent “piracy” and theft are being developed.

At the beginning of the 21st century, digital projection was only available at a handful of first-run cinemas in the United Kingdom, but as the projectors enter large-scale production and the cost comes down, digital presentation is likely to expand rapidly. The relatively high cost of the projectors may be countered by extensive leasing of the equipment and will also be offset by the large reduction in the costs of handling film prints.