At its inception, the film industry was based on a carnival art produced in large quantities, solely to be consumed by the public, but never preserved. Then, with the creation of major film production studios in France, Italy, the United States, and Germany, production intensified and film heritage increased considerably. However, it wasn't until the 1930s-40s that awareness of conserving all these films emerged, with the creation of the first film libraries and notably the 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 necessity of preservation became apparent. This awareness led to the establishment of strict standards regarding storage conditions, humidity control, and the choice of containers.
Digital restoration, strictly speaking, is an even more recent profession, due to the digital technologies inherent to its development.
To fully understand the issues surrounding digital restoration, one must first go back to the very beginning, and be 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 "laid" on. Over time, several bases have existed, each replacing the other for safety and preservation reasons.
nitrate → acetate → polyester
The emulsion is the actual image of the film. It consists of silver salts, sensitive to light, contained in a layer of gelatin. This is what is developed by chemical process. During filming, the raw film is contained in the camera and is exposed to light with varying aperture and speed settings 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 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. For example, nitrate is a very fragile film that, over time, tends to self-destruct and decompose. Significant image distortions due to the decomposition of the base can occur.
The main problem associated with acetate is what is known as vinegar syndrome, which causes a color shift. One may encounter copies that have turned completely red or green. It is then necessary to store these films in the best possible conditions to slow the acidification process and to scan the image to try to digitally restore all its color 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).
Starting in the 1950s, costly colorization processes gradually lost their monopoly to lighter, more affordable techniques. This is how the Glorious and its dye imbibition process, so dear to cinephiles and producers' wallets, was dethroned by Eastmancolor and films.
Thirty years pass, New Hollywood emerges 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 it has turned magenta. He raises the alarm. He is not alone in his concern, as Spielberg laments the damage to Jaws: "After five years, the blue disappears from the waters of Jaws while the blood spurting from Robert Shaw's mouth becomes increasingly red," and as you can see in the image, the passengers of the Alien spaceship sleep in a room that has turned pink. Scorsese then launches a campaign in the USA against the color deterioration of films shot on /Eastmancolor film.
At the Venice Film Festival, with the support of many 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 the trichrome dye imbibition known for its beauty and conservation quality. The Eastmancolor process involves a single print on a chromogenic development positive and inevitably deteriorates after 3 to 5 years. film emulsions suffer in particular from poor conservation of the cyan layer, hence the shift to red when the blue disintegrates.
After a petition that brought together all of Hollywood and film libraries worldwide, calling, among other things, for the return of , reviewed the chemical components of its products. The affair, due to its high profile, sparked the interest of a public that was almost entirely unaware of these issues related to film heritage preservation and restoration. It also marks Scorsese's and his accomplices' first steps towards creating institutions aimed at protecting this heritage, since in the late 1990s, he founded The Film Foundation. A foundation that oversees and finances numerous restorations.
To understand film, one must also know that a film starts from a negative, but there are then several generations of the film.
The negative is the film that was in the camera. It is the original film, and there is only one. The negative will be edited, but some effects or titles on the optical printer require superimposing film and thus intermediate prints. From the negative, interpositives, internegatives, and then copies are made, which will be shown in theaters. What we see in cinemas is actually a fourth-generation print from the original negative, which has therefore lost resolution and texture precision: it is like a photocopy of a photocopy of a photocopy... When restoring a film, one seeks to use as source material the most beautiful and best-preserved element possible. Often, the negative is chosen because it is the original element and thus has the highest possible resolution. But paradoxically, it is also something that audiences have never seen, as 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 image of one shot with the first of the next. These junctions, although fine and discreet, can sometimes create a slight over-thickness. Copies 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 part of the elements to be addressed during restoration.
Before moving on to digital restoration, the film undergoes REM, or Mechanical Restoration. The operator in charge of REM rolls out the film on a light table and checks its physical condition. The goal is to detect any defect that weakens the film, indicating poor overall condition, or risks hindering the scan's proper execution later. Indeed, the work in REM is twofold: analyzing the film, assessing its condition, and also consolidating and repairing it so it can withstand the tension it undergoes during scanning.
The defects targeted in REM include tears, damaged perforations, faulty or too sticky tape. The flexibility of the base is also checked—is it too dry, risking breakage during handling? Is it too sticky, risking emulsion deposition on the film's back when wound? Some institutions use film cans to control humidity levels and subsequently subject the film to high-temperature ovens, all to restore film flexibility for proper handling.
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 the best condition, and of the highest quality for digital restoration.
Once the film has been prepared and/or repaired, it can be scanned. Analog images are thus transformed into digital images and can be retouched, cleaned, and restored using software. Any digital intervention is entirely reversible, as one can always start again from the raw scan if later discovering more efficient restoration tools. This allows for starting from a clean base—the scan—that has captured a certain stage of the film's degradation.
Color grading is distinguished from digital restoration. It is a separate step, performed by a different profession and can be done before or after restoration, depending on the laboratories.
Color grading involves modifying the colorimetry of an image to harmonize the sequences of a film, the transitions between shots, or create a specific lighting ambiance. In heritage grading, the technician does not intrusively intervene in the image; they do not change a scene's warmth or alter the main ambiance tones. The idea is to restore the original film colors in the case of a faded copy that has turned all red or green, or to harmonize several elements from different sources to smooth transitions between them. If restoring an original negative, it has never been graded, so one will try to find a copy of the film to have a reference for re-creating the original film's grading. Similarly, if recreating tints for silent black and white tinted films, existing visual sources are closely examined to match the tints used at the time as closely as possible.
Grading is mainly done on Da Vinci's Resolve software.
Once the color grading is complete, we move on to digital restoration. This can be done using several software programs, 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 aim to "clean" the film to remove all alterations due to time, careless handling of elements, poor storage, or deterioration of the film itself. However, we do not correct filming defects (such as a boom in the frame or an unstable shot), development or printing defects (such as a veil or light leak). We leave everything that we know was present from the beginning.
Restoration is done in several steps.
This step smooths out the jumps that can occur during scanning. For example, the thickness of splices, mentioned earlier, can create a small jump when passing through the scanner gears, and film tears and subsequent repairs also disrupt the alignment of the film's perforations, leading to poor stabilization during scanning. But film instability can also come from the print itself, especially if dealing with copies. Indeed, during printing, the original film may not align precisely with the new support film, down to the millimeter, causing shifts in the perforations. The scanner's internal software, relying on the perforations to frame the image, references the latest generation of perforations. When scanning a copy, several generations of misaligned perforations can cause the stable base image to slightly jitter in the copy.
Once the image is stabilized, we can address flicker, known as "pompage lumineux" in French. This step is not mandatory as some films do not have this defect, unlike dust which is always present.
The software detects luminance jumps within the shot and unifies the brightness from one image to the next. It's like a color grading touch-up, but instead of matching one shot to another, it matches one image to the next within the same shot. This eliminates the annoying flickering effect. However, this step requires great caution because the software analyzes luminance variations from one image to the next, but a sudden movement or rapid pan can be mistaken for luminance variations. Thus, the tool's power is adjusted based on the shot being treated. A static shot with little movement will not be treated the same way as a panoramic battle scene.
This principle also applies to the next step: dust and scratch detection and removal.
For this, a filter analyzes all the images in a shot, pixel by pixel. For a given image, the filter examines each pixel in the previous and next images, and if the pixel's color does not match, the software considers the color change equivalent to a spot, whether black, white, or colored, as in color films. Hence the importance of properly stabilizing the image beforehand for the software analysis to be as effective as possible.
The variation in the pixel's color information may indeed correspond to dust, but sometimes it's just movement, a water or jewelry reflection, or the shine of teeth or eyes. The restoration technician must be careful to validate only dust detections, not a passing bird or a dazzling smile. The detected dust is automatically replaced by the filter through interpolation between the previous and next images to recreate the missing information.
Once the dust is eradicated, another automatic detection filter is used for scratches. The detection and information recreation principle is slightly different because the software looks for anything vertical and present in several consecutive images. Scratches can also be confused with vertical decor, bars, or wallpaper. The identified scratches are corrected not by interpolating the previous and next images but by retrieving information from the sides of the scratch, just to the right and left, and "stretching" these pixel details to fill the scratch groove.
After applying and verifying the automatic filters, only large defects remain on the image: tears, mold, significant stains, or glue residues. This is followed by meticulous retouching work, which can take various forms: recovering missing information from adjacent images, manual interpolation between two frames, or image-by-image retouching, similar to Photoshop.
All these software manipulations aim to produce a version of the film as faithful as possible to the original work. However, the restoration's goal greatly influences the treatment choices. Indeed, restoration for archival purposes will not follow the same criteria as a version intended for film festivals, television broadcasts, or DVD releases. The requirements vary depending on the projection and distribution context. For a general public television broadcast, more significant touch-ups might be made, sometimes removing original imperfections, to meet current visual standards. A concrete example is the camera hair. During film shooting, despite meticulous cleaning of the camera before each take, microscopic particles may remain inside, particularly around the edges of the frame. These residues, once photographed, create a characteristic effect on the image's edges, known as "camera hair" due to its filamentous appearance. Although visually annoying, this type of defect, intrinsic to the image and uniformly present throughout a shot, traditionally escaped restoration possibilities as it was difficult to treat and remove. However, new AI tools now make it possible to treat and remove this "defect." But this raises an ethical question: should we really remove it? The camera hair is part of the film image's essence, just like the grain and certain colorimetry. Removing it would denature the film image, erasing defects inherent to its existence.
In reality, depending on the restoration's commissioners, its budget, and whether it's for archival or commercial purposes, "how far do we go in restoration" is always questioned. The profession is undergoing technological transformation, tools are evolving, and ethical and archival considerations will continue to evolve with them.