Glossary - A to Z
The answer print, also called the first trial print, is the first print made from edited film and sound track. It includes fades, dissolves and other effects. It is used as the last check before running off the release prints from the internegatives.
Best Light (pass)
Similar to a one light pass but, by implication, the timer has studied the film more thoroughly to select a timing light that will agree with the majority of the footage.
Camera negative (film)
Camera negative film is designed to capture as much detail as possible from scenes. This not only refers to its spatial resolution but also its dynamic resolution. Modern camera negative stock has almost 10 stops’ exposure range and so is able to record detail in both the low-lights and the highlights which are well beyond the range that can be shown on the final print film. This provides latitude to compensate for over or under exposure during the shoot or to change the look of a scene. The latitude is engineered into the film stock by giving it a very low gamma of around 0.6. Exposed and developed camera colour negative film has an orange tint and is low in contrast – differing greatly from the un-tinted and high contrast print film. As not only the blue, but also the red and green layers of the film are sensitive to blue light, the orange layer is added below the blue layer to stop blue light going further. All types of film stocks use orange dye but for print films it is bleached away during processing. There are numerous stocks available. High speed stocks work well in lower lights but tend to be more grainy. The opposite is true for low speed stocks.
An RGB bitmap file format (extension .cin) developed by Kodak and widely used for storing and transferring digitised film images. It accommodates a range of film frame sizes and includes up to full Vista Vision. In all cases the digital pictures have square pixels and use 10-bit log sampling. The sampling is scaled so that each of the code values from 0-1023 represents a density difference of 0.002 – describing a total density range of 2.046, equivalent to an exposure range of around 2,570:1 or about 11.3 stops.
Note that this is beyond the range of current negative film. The format was partly designed to hold virtually all the useful information contained in negatives and so create a useful ‘digital negative’ suitable as a source for post production processing and creating a digital master of a whole programmer.
See also: 10-bit log, DPX
Colour Timing/Correction (a.k.a. Grading)
The colour of film exposed and processed in a laboratory is controlled by separately altering the amount of time that the red, blue and green lights are used to expose the film. This is referred to as colour timing and its effect is to alter contrast of R, G and B to create a required colour balance. In a lab, colour timing is usually applied at the point where the edited negative is copied to the master interpositive but can be done later at other points if required. In the digital film process, colour timing is applied at any required point, as required. In addition there is far more flexibility for colour control with gamma, hue, luminance, saturation as well as secondary colour correction. In addition, the results can be seen immediately and projected onto a large cinema screen and further adjusted if required. The images have precise colour settings to show the results as if output via film, or digitally.
See also: Lights, Timing
Refers to the digital distribution and projection of cinema material. High definition television and the continuing development of digital film projectors using DLP and D-ILA technology allow high quality viewing on large screens. The lack of all-too-familiar defects such as scratches and film weave – even after many showings – already has its appeal. Besides quality issues, D-cinema introduces potential new methods for duplication and distribution, possibly by satellite, and more flexibility in screening.
An instrument used to measure the density of film, usually over small areas of images. The instrument actually operates by measuring the light passing through the film, which is a factor of transmittance, and green film will transmit more light than red or blue. Also, negative film differs from positive film. So two sets of colour filters are used to measure Status M density for camera negative and intermediate stocks (orange/yellow-based) and Status A for print film.
The density (D) of a film is expressed as the log of opacity (O). [D = Log 10 O] Using a logarithmic expression is convenient as film opacity has a very wide range and the human sense of brightness is also logarithmic.
If supplying a digital cinema the ‘lab’ operation can be streamlined and simplified as the ‘film’ can remain in digital form for its grading and editing as well as for effects. Adding the soundtrack allows everything to be placed onto a single digital master which is, effectively, a near-perfect copy of the scanned cut negative. Unlike film which can only be reproduced by one-to-one contact (hence all the interpositive and internegative copying to build up the numbers), digital media is reproduced by a one-to-many operation. All distribution copies, master copies, etc., can be made at one time. This is quicker, cheaper and avoids any wear on the master version. The distribution can use digital channels, currently hard drives are distributed and copied to servers at digital cinemas. There has also been direct distribution via satellite or broadband, although this is less widespread. With relatively low data speeds delivery can be overnight, where ultimately high data speeds could be used for live showings direct from the studio/distributor.
Digital Intermediate (DI)
Generally digital intermediate refers to a digital file or files resulting from a scan of a film (usually negative) original that is used for the editing, effects and grading/colour correction. It is the material that is used in digital labs and constitutes the whole film. As such it should carry all the useful information that is contained in the camera negative to provide both the latitude and sharpness of the original for which scanning at 2k resolution, 10-bit log is ideal. It could also apply to material directly recorded from a digital TV camera – from DV through to HDCam, DVCPRO HD or Viper FilmStream Data camera.
The film lab accepts exposed footage and eventually delivers edited and graded masters – in the form of internegatives – to the production labs to produce large numbers of release prints. Although the boundaries may vary, generally the digital lab accepts developed camera negative and outputs edited and graded internegative master for a whole or part of a feature. However, the operational and decision processing between differ greatly from the film lab, not least because of the interactive nature of the operation. In the digital lab, decisions become on-screen reality and seen in full context as they are prepared – no waiting for the ‘chemical’ lab. Grading, dissolves, cuts and effects can be seen immediately and on a big screen – if needed.
The interactive process can be more creative and gives complete confidence that the decisions work well. Using large-scale digital storage means that long sections of finished material can be sent for output to the digital lab’s film recorder, exposing 2000-foot reels at a time.
SMPTE file format for digital film images (extension .dpx) – ANSI/SMPTE 268M-1994. This uses the same raster formats as Cineon and only differs in its file header. See Cineon file
The measurement of the range of brightness in a scene expressed as a ratio or the Log 10 of the ratio. Typically the lighting cameraman will try to keep the scene to less than 40:1 (Log = 1.6) to avoid loss of detail in the print. A 100:1 (Log = 2) contrast range in the scene is a typical maximum.
Any film editing, other than cuts, has traditionally required the use of a film optical lab where dissolves, wipes and any compositing work for making effects shots can be carried out. The techniques are highly refined but lack interactivity and are not lossless – hence the jump in colour and quality before and after a film dissolve. Such effects work is increasingly undertaken in digital equipment. For this the appropriate camera negative footage is scanned and stored – usually onto disks. This is then digitally processed in an effects workstation, which can be lossless irrespective of the number of effects layers, provided that the images remain uncompressed, and the results can be seen immediately. The completed effects shots are then output to a film recorder to produce new negative footage to be cut in with the rest.
Exposure refers to the amount of light that falls on a film or light sensor. In a camera this is controlled by both time with the shutter, and the effective lens aperture, referred to as the F number or T number.
Unlike pre-HD television, which had only two image formats, 525/60I and 625/50I, 35 mm film has many. Of these the most common are Full Frame, which occupies the largest possible area of the film, Academy and Cinemascope. The scanning for these is defined in the DPX file specification as follows:
These scan sizes generally represent the valid image size within the total frame size indicated by full frame. It is generally considered that all scanning is done at full frame size as this avoids the complexity of adjusting the scanner optics or raster size with risks associated with repeatability and stability.
In addition, different camera apertures can be used to shoot at different aspect ratios. All these (below) are ‘four perf’ (a measure of the length of film used) and so all consume the same amount of stock per frame. Note that scanners (and telecines) typically change scan size to maintain full 2k images regardless of aspect ratio. It is no longer normal for work to be scanned at a fixed full frame size. There are many more 35 mm formats in use. For lower-budget movies Super 16 is a good match for post production in standard definition television (601).
Equipment which inputs digital images and outputs exposed negative. In this area, CRT and laser-based technology recorders expose high-resolution images onto film. Arguments rage over the fastest output device to film, CRT-based recorders are allegedly fastest outputting 2k images onto camera negative stock at the rate of one per second.
A general term for a device that creates a digital representation of film for direct use in digital television or for digital intermediate work. For television, film scanners are now replacing traditional telecines. For film, they should have sufficient resolution to hold the full detail of the film so that, when transferred back to film, the film-digital-film chain can appear as an essentially lossless process. For this, film scanners are able to operate at greater than HD resolutions (1920 x 1080). 2k is the most commonly used format but 3k and 4k are also in use – mainly for effects-related work. The output is data files rather than the digital video that would be expected from a traditional telecine.
The dynamic resolution needs to fit with the on-going process. If the digital material is treated as a ‘digital camera negative’ to act as a digital intermediate, then it must retain as much of the latitude of the negative as possible. In this case the material is transferred with a best light pass and the linear electronic light sensors, often CCDs, have to sample to at least 13 bits of accuracy (describing 8192 possible levels). Using a LUT, this can be converted into 10-bit log which holds as much of the useful information but does not ‘waste’ data by assigning too many levels to dark areas of pictures. Note that this is different from using a telecine to transfer film to video. Here, normal practice is to grade the film as the transfer takes place so additional latitude is not required in the digital state. Here 10 or 8 bits linear coding is sufficient.
Gamma has several meanings. In the video world a CRT television monitor’s brightness is not linearly proportional to its driving voltage. In fact the light output increases rapidly with drive. The factor, gamma of the CRT, is generally calculated to be 2.6. This is compensated for in TV cameras by a gamma of 0.45 giving an overall gamma of 0.45 x 2.6 = 1.17 – adding overall contrast to help compensate for domestic viewing conditions.
In film gamma describes the average slope of the D/Log E curve over its most linear region. For negative stocks this is approximately 0.6, for intermediate stocks this is 1.0 and for print stocks 3.0. This gives a system gamma of 0.6 x 1 x 3 = 1.8. This overall boost in contrast is much reduced due to flare and auditorium lighting conditions.
Grading (Film & Digital)
Individually adjusting the contrast of the R, G and B content of pictures to alter the colour and look of the film. Traditionally this has been controlled in film labs by adjusting the amount of R, G and B light to alter the exposure of print to negative – known as colour timing. This is commonly applied during copying to interpositives in order to achieve a shot-to-shot and scene-to-scene match by altering the overall colour balance of the images. This is not a hue shift but a control of the proportions of R, G, and B in the final images. For film being transferred for video post production in a telecine, grading using lift, gain and gamma is executed shot-by-shot, as the film is transferred.
Today there is a growing move toward digital grading which involves one continuous best-light pass through a film scanner with the result being stored to a data server. Grading then takes place purely in the digital domain and without film in the telecine. Not only does this free up the scanner for other work but it also involves far less film handling and so is far quicker and involves less risk of damaging the film. Note that digital grading requires that there is sufficient latitude in the digital material to allow a wide range of adjustment. This involves using either linear sampling at 13 bits or more, or 10-bit log DPX/Cineon files.
As a part of the chemical lab film intermediate process internegatives are by contact printing from interpositives. These very much resemble the cut negative. The stock is the same as for interpositives: slow, very fine grain with a gamma of 1, and the developed film is orange-based. Again, to increase number, several interpositives are copied from each internegative. These are then delivered to production labs for large scale manufacture of release prints.
This is a first part of the chemical lab intermediate process where a positive print of film is produced from the cut (edited) camera negative. Interpositives are made by contact printing onto another orange-base stock. In order to preserve as much detail as possible from the negative, including its dynamic range, interpositive material is very fine grain, slow, and has a gamma of 1. During the copying process, grading controls are used to position the image density in the center of the interpositive material’s linear range. As a part of the process of going from one camera negative to, possibly, thousands of prints, a number of interpositives are copied from the negative.
Latitude is the capacity of camera negative film to hold information over a wider brightness range than is needed for the final print. This provides a degree of freedom that is needed because it is impossible to see if the exposure is totally correct until the film comes back from the laboratory – long after the set has been struck and everyone has gone home. Latitude provides room for later adjustment in printing to compensate for over or under exposure. Using digital cinematography, it is possible to see the results immediately and make any required adjustment at the shooting stage. This procedure can reduce the need for a very wide latitude (which cannot extend to the release prints) by ensuring the lighting and set ups are always correct at the shoot.
Look-Up Table (LUT). This refers to a table of conversion factors that are used to transfer information between two differing but related systems. For example, there is often a requirement to look at digital image material to see what it looks like on a CRT, digitally projected and projected via film – all of which have different characteristics. A fast and relatively simple way to process the digital material so that it looks as it should on all displays is to multiply the level of each pixel by a unique number stored in a LUT that corresponds just to that value. Thus a linear CCD output can be processed to drive a CRT which has a highly non-linear ‘gamma’ characteristic. In addition it provides a path between linear electronically scanned images and the logarithmic world of film.
Film that shows the shot scene as negative images. Negative material is used in several stages of the traditional film production chain that culminates in release prints.
One - Light
In a one-light pass, all the material is given the same exposure during printing in a film processing laboratory. This is the simplest, quickest and cheapest way to print all the film and the results are typically used for making rushes, dailies, etc. These are often subsequently telecined and recorded to videotape as a reference for the offline decision-making process.
Short for perforations. It is a way to describe some information about the format of images on 35 mm film by how many of the perforations, or sprocket holes, are used per image. For example, Full Frame is 4 perf.
Film stock designed specifically for distribution and exhibition at cinemas. Unlike negative film, it is high contrast and low on latitude. This is designed to give the best performance when viewed at cinemas. Obviously the release print has to be clear of the orange base so this is bleached out during processing.
The illumination used to expose film in the processing laboratory. ‘White’ light is passed through red, blue and green filters so that the exposure to each can be individually controlled. Film is contact printed, placing the new film stock against the processed film that carries the images. The amount of light can be varied to provide the required exposure to show more detail in the highlights or the shadows or to keep to the mid-range of the scene brightness. To print an overexposed negative will require higher values and underexposed lower values. A change of 1 in the value represents 1/12 of a stop adjustment in exposure. Differential adjustments of the values provides basic colour correction (timing). The values for the lights are recorded as grading (timing) numbers onto disk or paper tape.
Digital projectors input digital images and project them onto cinema-sized screens. Huge advances in this technology in the last five years have been one of the driving forces behind digital film. There are two prominent technologies in the large projector area, D-ILA from JVC and DLP from Texas Instruments. The viewing public is generally very impressed with the results as, without film’s scratches, dirt and weave, they are treated to consistent high quality results.
Status M and Status A
A ratio of amount of light where one stop represents a doubling or halving of the light. The operating range of film and electronic light sensors, such as CCDs, are quoted in stops. Typically, a camera’s shutter speed and the lens’s aperture setting restrict the light arriving at the sensors/film so the mid brightness of the required scene corresponds to the middle of the sensor’s or film’s sensitivity range for the required shutter speed. Stops are simply the expression of a ratio, not absolute values. As they represent doubling of light, they are actually powers of 2. So 1 stop = x 2, 2 stops = x 4, 3 stops = x 8, 4 stops = x 16 etc.
Note that cine lenses are often marked in f-stops (white) and T-stops (red). The former is a geometric relationship between focal length and aperture and does not take into account how much light is lost within a lens. T-stops do and represent the real working values. So, on a lens that loses a full stop in transmission (i.e. a 50-percent loss), f/8 would result in the same exposure as T11. F and T values are usually close on prime lenses but zoom lenses show a greater difference.
As ‘best light’ but a technical grade is often a lower contrast scan to include all highlights and lowlights. A best grade is often of correct contrast but with some clipping of high or low lights.
Timing and Timer
Timing refers to the amount of the separate R, G and B lights that are used to expose film in a laboratory as a part of the grading process. The term is sometimes also applied to colour correction (grading) during telecine transfers. The timer is one who decides and controls the lights’ timing.