When a cinematic release is shot on film, whatever format chosen, typically 35mm, the process to the cinema has remained unchanged for many years. The camera negative after developing, ‘rush prints’ are taken and viewed to make sure the crew captured all the action and to check that there were no mishaps on the shoot. The production can have moved on several days by the time the rush print gets back to the director, or he/she may even have to rely on someone else’s judgement that all has been captured.

An initial optical grade may even be done on these rushes to ‘normalise’ the image for viewing and for editing purposes. These rushes are compiled into what we would recognise as the final film, which is known as the ‘work print’. The original negative is then finally cut to this ‘work print’, which in itself is risky because if you make a mistake at this stage you will never be able to recover that cut frame, because you can never rejoin the cut invisibly. The work print essentially provides a cutting list.

Along the edge of each negative (also the work print) is a unique numbering, or keycode. Keycodes are unique to every piece of film, they are exposed into the raw stock at manufacture, which only become visibly during processing. Through these codes any individual frame can be identified within the production. Precise matching is made using a dual gang synchronizer, the work print running alongside the negative and visually comparing the action and these keycodes.

From this edited negative an inter positive (IP) is struck which is usually known as the safety copy, in case of damage to the original. Then an inter negative is struck which has no splices and has scene-to-scene grading corrections which can then be printed at high speed as a ‘one light’ which produces the print we view at the cinema.

It is useful to note that that these copies incur quality losses, so some detail of the original negative is lost, something that the Digital Intermediate process does not.

 

Colour Grading – Lab Style

Film is shot under many conditions and differences in light, film density in the raw film stock and exposure needs to be evened out to provide continuity between scenes back to back. They may have been shot days apart, on different locations or it just may have become overcast part way through the days shoot. Even pick ups months apart may all have a different hue, due to developing differences (the bath may be slightly different), different film stocks or even a different filter can change the look. Negatives must be graded, sometimes refered to as colour timing or what we think of as colour correction.

Traditional optical lab work only allows the overall balance and density to be changed, single colours in optical grading cannot be fettled without affecting the entire image. Without going into the full logistics of how an optical printer works, the basic idea is that the full white printing light is separated in to its red, green and blue components. Each of which is passed through a light valve to adjust the intensity before recombining the sources at the printing gate. These valves are opened and closed by fractional amounts, letting controlled amounts of light through which are known as printer settings or lights.

The printer lights are determined during the grading session before printing, a change of one point of colour will be barelyperceptible. If a negative is overexposed by one stop in the camera, it takes approximately +7 printer points to correct for this. Another point, which can cause confusion, grading corrections work in reverse of how you would think – adding two points green actually removes green. Confused – well it’s not easy and can be seen as an art.

Grading ultimately cannot compensate for under-exposed negative, and some shadow detail will be lost however much the print is lightened – some may refer to this as becoming ‘milky’.

It should also be noted the tolerance in projection standards around the globe will affect the look anyway, due to the intensity of the light source, even down to the glass separating the auditorium from the projection room will change the colourimmetry!

Some labs use a computer to log these printer light changes on every scene, using the frame count cue (FCC) these trigger points, cue the mechanical changes in printer lights. However some still use punch paper tape that runs alongside the film, as the name suggest punched holes trigger these printer light changes – sounds archaic but has proved extremely reliable.

Remember we are still watching theatrical releases at the cinema, therefore even though we have gone through a DI process, we are still reliant on the lab to produce the final print runs.

 

The Future

The move towards DI away from the optical process’ of old is well under way. Most films you see in the cinema will have been through a Digital Lab. The process allows a much more creative, controlled, flexible and intricate style compared to optical grading. Plus films are rarely viewed in a ‘film only’ cinema now – a huge amount of cinemas with the help of the Arts Alliance (UK) have opted to go digital. Films are delivered on a hard drive, which are ingested onto a server and then projected as a high quality image, thus never going back to film. This is a compelling arguement in itself to take your production through the Digital Intermediate route.

At some point if the project is captured on film it needs to be scanned or telecinied for multiple formats to be struck from this master: D-Cinema, HD, DVD and a myriad of television standards will be struck from the Digital Intermediate. Many labs now are offering the full DI route as well as the standard lab optical process' offering a 'one stop shop' all under one roof.