In its early days, the film industry was based on a fairground art produced in large quantities, solely for public consumption, but never preserved. Then, with the creation of major film production studios in France, Italy, the United States, and Germany, production intensified and the cinematic heritage grew considerably. However, it was only in the 1930s-40s that awareness of preserving all these films emerged, with the creation of the first film libraries and notably the FIAF in 1938.
The initial instincts were to collect as many films as possible and show them to the public. It was only later, faced with the increasing deterioration of film reels, that the need for conservation became apparent. This awareness led to the development of strict standards regarding storage conditions, humidity control, and the choice of containers.
Digital restoration itself is an even more recent profession, due to the digital technologies inherent to its development.
To fully understand the challenges of digital restoration, we must return to the fundamentals and become aware of everything inherent to film, its material, and its properties.
Film consists of two parts: the base, which is the shiny side of the film, and the emulsion, the matte side.
The base is what the image is "placed" on. Over time, several bases have existed, one replacing the other for safety and preservation reasons.
nitrate → acetate → polyester
The emulsion is the actual image of the film. It consists of light-sensitive silver salts contained in a layer of gelatin. This is what is developed by chemical process. During filming, the unexposed film contained in the camera is exposed to light at a more or less large and fast aperture and speed, adjusted to obtain the desired image. If the film is exposed for too long, too much light will enter and the image will be all white. If the film is not exposed enough, the lack of light will create an image that is too dark.
During filming, the image is only latent. It is revealed by passing through several chemical baths, which, in reaction to the silver salts, will produce the image.
Several types of defects can be found on film. Some are related to the base. Nitrate, for example, is a very fragile film that, over time, tends to self-destruct and decompose. Major image deformations due to the decomposition of the base can occur.
The main problem with acetate is what is called vinegar syndrome, which causes a color shift. We can find ourselves faced with copies that have become all red or all green, it is then necessary to store these films in the best possible conditions to slow down the acidification process and scan the image to try to digitally recover all its colorimetric information.
Other defects, more related to the passage of time, the use of copies, and storage will attack the film's emulsion. These can include dust accumulated on the film, scratches, mold (due to poor storage, and/or humidity), tears, or flicker (light pumping).
From the 1950s onwards, very expensive colorization processes gradually gave way to lighter and more affordable techniques. This is how Glorious Technicolor and its imbibition process, so dear to cinephiles' eyes and producers' wallets, was dethroned by Eastmancolor and Kodak films.
Thirty years pass, New Hollywood settles in and produces great films such as 2001: A Space Odyssey (Stanley Kubrick, 1968), Alien (Ridley Scott, 1979), and Taxi Driver (Martin Scorsese, 1976). In 1980, on the occasion of a special screening of the latter, Martin Scorsese retrieves his negative and discovers that it has turned magenta. He sounds the alarm. He's not the only one affected as Spielberg deplores the damage to Jaws: "After five years the blue disappears from the waters of Jaws while the blood gushing from Robert Shaw's mouth becomes redder and redder," he stated, and as you can see opposite, the passengers of Alien's space freighter are sleeping in a room that has turned pink. Scorsese then launches a campaign in the USA against the color deterioration of films shot on Kodak/Eastmancolor film.
At the Venice Film Festival, with the support of numerous filmmakers such as Michelangelo Antonioni and journalists from the international press, he makes a spectacular demonstration of the effects of time on color films. He emphasizes the process that succeeded Technicolor's three-strip imbibition, renowned for its beauty and quality of preservation. The Eastmancolor process consists of a single print on a chromogenic development positive and inevitably deteriorates after 3 to 5 years. Kodak film emulsions particularly suffer from poor preservation of the cyan layer, hence the shift to red when the blue disintegrates.
After a petition that gathered all of Hollywood and film libraries around the world and called for, among other things, a return to Technicolor, Kodak reviewed the chemical components of its products. Through its loud noise, the affair aroused the interest of a public that knew almost nothing about these issues related to the preservation of film heritage and its restoration. It also marks the first gestures of Scorsese and his accomplices towards the creation of institutes aimed at protecting this heritage, since at the end of the 1990s, he created the Film Foundation. A foundation that oversees and finances a large number of restorations.
To understand film, you also need to know that a film starts from a negative, but that there are then several generations of the film.
The negative is the film that was in the camera. It's the original of the film and there's only one. The negative will be edited, but certain effects or tricks or title sequences require a superimposition of film and therefore intermediate prints. From the negative, interpositives, internegatives, and then copies are made, which will then be shown in theaters. What we see in cinemas is actually a fourth generation drawn from the original negative, which has therefore lost resolution and texture precision: it's as if it were a photocopy of a photocopy of a photocopy...
When we want to restore a film, we try to have as source material the most beautiful and best preserved element possible. Often we will choose the negative because it is the original element, and therefore with the highest possible resolution. But paradoxically, it's also something that viewers have never seen, because a negative is never projected in theaters.
The issue of editing splices extends from the original negative to the film copies. On the negative, glue splices fuse the last frame of one shot with the first of the next. These junctions, although thin and discreet, can sometimes create a slight thickening. Copies, on the other hand, generally reproduce these splices photographically. However, subsequent repairs, often made with tape, can create new problems. Over time, this tape can degrade, producing a greasy substance that alters the image. These defects are among the elements to be addressed during restoration.
Before moving on to digital restoration proper, the film will go through REM, which stands for Mechanical Reconditioning. The operator in charge of REM unwinds the film on a light table and checks its physical condition. This involves detecting any defects that weaken the film, signs of poor general condition, or risks that could hinder the smooth running of the scan later. Indeed, the work at REM is twofold: analyzing the film, making an inventory of its condition, but also consolidating and repairing it so that it can withstand the scan and the tension it undergoes during it.
The defects targeted in REM are tears, damaged perforations, failing tape or, conversely, tape that is too sticky. We also check the flexibility of the support, is it too dry, at the risk of breaking during handling? Is it too sticky, at the risk of having emulsion that could be deposited on the back of the film when it is rolled up? Some institutions proceed to put films under bell jars, to be able to control the humidity level as best as possible, and conversely then to high-temperature oven passages, all this in order to restore flexibility to the film for smooth running.
It is also possible to have several elements of the same film and compare them during REM, to determine which is the most suitable, in better condition, and of better quality for digital restoration.
Once the film has been prepared and/or repaired, it can be scanned. The analog images are thus transformed into digital images and we can then retouch them, clean them, restore them, on software. Any digital intervention is therefore entirely reversible, because we can always go back to the raw scan, if we later come to discover new, more powerful restoration tools. This allows us to start from a healthy base, the scan, which has frozen in time a certain stage of degradation of the film.
We distinguish color grading from digital restoration proper. It is a separate step, carried out by a different profession and which can be carried out before or after restoration, depending on the laboratories.
Color grading consists of modifying the colorimetry of an image to harmonize the sequences of a film, the connections between shots or create a particular light atmosphere. In the context of heritage grading, the technician does not intervene intrusively in the image; he will not change the warmth of a scene, or modify the hues of the main atmospheres. The idea is to find the original colors of the film in the case of a shifted copy, which would have become all red or all green, or to harmonize several elements from different sources to smooth the transitions between elements. If we restore an original negative, it has never been graded so we will try to find a copy of the film to have a base on which to rely to recreate the original grading of the film. Similarly, if we have to recreate tints for black and white silent films that were tinted, we approach existing copies and visual sources that we can look at on a light table, in order to get as close as possible to the tints used at the time.
Color grading is mainly done on Da Vinci's Resolve software.
Once the color grading is finished, we move on to digital restoration. This can be done on several software, the main ones being Diamant from HS Art, Phoenix and Nucoda from Digital Vision (now Filmworkz), and DRS Nova from MTI.
The principle of digital restoration is as follows: we want to "clean" the film in order to remove all alterations related to time, careless handling of elements, poor storage or deterioration of the film itself. However, we do not correct a shooting defect (a boom entering the frame, an unstable shot...), a development or printing defect (a veil, a light leak...). We leave everything we know was present from the beginning.
Restoration is done in several steps.
This step allows us to "smooth out" the jumps that can occur during scanning. For example, the extra thickness of splices, mentioned earlier, can create a small jump when passing through the scan gears, film tears and subsequent repairs also disrupt the alignment of the film perforations and result in poor stabilization during scanning. But the instability of a film can also come from printing, if we are dealing with copies. Indeed, during printing, the original film may not be exactly in front of the new support film, to the millimeter, and thus create misalignments at the perforation level. The scanner's internal software, basing itself on the perforations to respect the frame of the image, will take as reference the last generation of perforations. When scanning a copy, several generations of misaligned perforations follow one another between the stable base image and that of the copy, which can thus move slightly.
Once the image is stabilized, we can treat the flicker, called light pumping in French. This step is not mandatory because some films do not have this defect, unlike dust which is always present.
The software detects jumps in brightness within the shot and unifies the luminance from one image to another. It's like a color grading retouching, but instead of connecting one shot to another, it connects one image to another within the same shot. We thus lose the very unpleasant flickering effect to the eye. However, this step requires a lot of vigilance because the software analyzes the variations in brightness from one image to another, but a sudden movement or a rapid pan can be considered as variations in brightness. Thus, we adjust the power of the tool according to the shot we are treating. A fixed shot with little movement will not be treated in the same way as a battle scene in panoramic view.
This principle also applies to the next step: dust detection and removal.
To do this, we use a filter that analyzes all the images of the same shot, pixel by pixel. For a given image, the filter examines each pixel in the image before and each pixel in the image after. And if the color of the pixel does not match, the software considers that the color change is equivalent to a stain, whether it is black, white or colored as for color films. Hence the importance of having well stabilized the image beforehand so that the software analysis of this step is as effective as possible.
The variation in the color information of the pixel can indeed be due to the presence of dust, as well as movement, a reflection in water or a jewel, or even the shine of teeth and eyes. The restoration technician must be vigilant to validate only dust detections and not a passing bird or a too bright smile. The dust thus detected is automatically replaced by the filter by an interpolation between the image before and the image after to recreate the missing information.
Once the dust is eradicated, we tackle scratches using another automatic detection filter.
The principle of detection and recreation of missing information is a bit different because the software seeks to identify everything that is vertical and present on several consecutive images. Scratches in this case can also be confused with vertical decor, bars or wallpaper.
The real scratches identified are corrected, not by interpolations of images before and after, but by recovering information on the sides of the scratch, just to the right and just to the left, and by "stretching" the information of these pixels to fill the groove of the scratch.
Once the automatic filters have been applied and verified, only large defects persist on the image: tears, mold, significant stains or glue residues. Then follows a meticulous retouching work. This can take various forms: recovery of missing information on adjacent images, manual interpolation between two frames, or frame-by-frame retouching, similar to Photoshop.
All these software manipulations result in producing a version of the film as faithful as possible to the original work.
However, the purpose of the restoration greatly influences the choices in the treatments applied. Indeed, a restoration for heritage purposes for archives will not follow the same criteria as a version intended for film festivals, television broadcast or DVD release. Requirements vary depending on the context of projection and distribution. Thus, for a general public television broadcast, we may be led to make more significant retouches, sometimes removing original imperfections, in order to adapt to current visual standards.
A very concrete example can be that of the camera hair. During filming on film, despite meticulous cleaning of the camera before each take, microscopic particles can remain inside it, especially on the edges