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Color grading is apost-production process common tofilmmaking andvideo editing of altering the appearance of an image for presentation in different environments on different devices. Various attributes of an image such ascontrast, color,saturation, detail,black level, andwhite balance may be enhanced whether for motion pictures, videos, or still images.
Color grading andcolor correction are often used synonymously as terms for this process and can include the generation of artistic color effects through creative blending andcompositing of differentlayer masks of the source image. Color grading is generally now performed in a digital process either in a controlled environment such as acolor suite, and is usually done in a dim or dark environment.
The earlierphotochemical film process, referred to ascolor timing, was performed at afilm lab duringprinting by varying the intensity and color of light used to expose the rephotographed image. Since, with this process alone, the user was unable to immediately view the outcome of their changes, the use of a Hazeltine color analyzer was common for viewing these modifications in real time. In the 2000s, with the increase of digital technology, color grading inHollywood films became more common.
Color timing is used in reproducing film elements. "Color grading" was originally a lab term for the process of changing color appearance in film reproduction when going to theanswer print or release print in the film reproduction chain. By the late 2010s, this film grading technique had become known ascolor timing and still involved changing the duration of exposure through different filters during the film development process. Color timing is specified inprinter points which represent presets in a lab contact printer where 7 to 12 printer points represent onestop of light. The number of points per stop varied based upon negative or print stock and different presets at film labs.
In a film production, the creative team would meet with the “lab timer” who would watch a running film and make notes dependent upon the team's directions. After the session, the timer would return to the lab and put the film negative on a device (the Hazeltine) which had preview filters with a controlled backlight, picking exact settings of each printer point for each scene. These settings were then punched onto a paper tape and fed to the high-speed printer where the negative was exposed through a backlight to a print stock. Filter settings were changed on the fly to match the printer lights that were on the paper tape. For complex work such as visual effects shots, "wedges” running through combinations of filters were sometimes processed to aid the choice of the correct grading.
This process is used wherever film materials are being reproduced.
With the advent of television, broadcasters quickly realised the limitations oflive television broadcasts and they turned to broadcasting feature films from release prints directly from atelecine. This was before 1956 whenAmpex introduced the firstQuadruplex videotape recorder (VTR) VRX-1000. Live television shows could also be recorded to film and aired at different times in different time zones by filming a video monitor. The heart of this system was thekinescope, a device for recording a television broadcast to film.[1]
The early telecine hardware was the "film chain" for broadcasting from film and utilized a film projector connected to a video camera. As explained byJay Holben inAmerican Cinematographer Magazine, "The telecine didn't truly become a viablepost-production tool until it was given the ability to perform colour correction on a video signal."[2]
In acathode-ray tube (CRT) system, an electron beam is projected at a phosphor-coated envelope, producing a small spot of light. This beam is then scanned across a film frame from left to right, capturing the "vertical" frame information. Horizontal scanning of the frame is then accomplished as the film moves past the CRT's beam. Once this photon beam passes through the film frame, it encounters a series ofdichroic mirrors which separate the image into its primary red, green and blue components. From there, each individual beam is reflected onto aphotomultiplier tube (PMT) where the photons are converted into an electronic signal to be recorded to tape.
In acharge-coupled device (CCD)telecine, a white light is shone through the exposed film image onto aprism, which separates the image into the three primary colors, red, green and blue. Each beam of colored light is then projected at a different CCD, one for each color. The CCD converts the light into an electronic signal, and the telecine electronics modulate these into a video signal that can then be color graded.
Early color correction on Rank Cintel MkIII CRTtelecine systems was accomplished by varying the primary gain voltages on each of the three photomultiplier tubes to vary the output of red, green and blue. Further advancements converted much of the color-processing equipment from analog to digital and then, with the next-generation telecine, the Ursa, the coloring process was completely digital in the 4:2:2color space. The Ursa Gold brought about color grading in the full 4:4:4 color space.[2]
Color correction control systems started with the Rank Cintel TOPSY (Telecine Operations Programming SYstem) in 1978.[1] In 1984Da Vinci Systems introduced their first color corrector, a computer-controlled interface that would manipulate the color voltages on the Rank Cintel MkIII systems. Since then, technology has improved to give extraordinary power to the digital colorist. Today there are many companies making color correction control interfaces including Da Vinci Systems andPandora International.
Some telecines are still in operation in 2018.
Some of the main artistic functions of color correction (digital color grading) include:[1]
Note that some of these functions must be prioritized over others; for example, color grading may be done to ensure that the recorded colors match those of the original scene, whereas other times, the goal may instead be to establish a very artificial stylized look. Color grading is one of the most labour intensive parts of video editing.
Traditionally, color grading was done towards practical goals. For example, in the filmMarianne, grading was used so that night scenes could be filmed more cheaply in daylight. Secondary color grading was originally used to establish color continuity; however, the trend today is increasingly moving towards creative goals such as improving the aesthetics of an image, establishing stylized looks, and setting the mood of a scene through color. Due to this trend, some colorists suggest the phrase "color enhancement" over "color correction".
Primary color grading affects the whole image by providing control over thecolor density curves of red, green, blue color channels, across the entire frame. Secondary grading can isolate a range of hue, saturation and brightness values to bring about alterations in hue, saturation and luminance only in that range, allowing the grading ofsecondary colors, while having a minimal or usually no effect on the remainder of the color spectrum.[1] Usingdigital grading, objects and color ranges within a scene can be isolated with precision and adjusted. Color tints can be manipulated and visual treatments pushed to extremes not physically possible with laboratory processing. With these advancements, the color grading process has become increasingly similar to well-established digital painting techniques, ushering forth a new era ofdigital cinematography.
The evolution of digital color grading tools has advanced to the point where the colorist can use geometric shapes (such as mattes or masks in photo software such asAdobe Photoshop) to isolate color adjustments to specific areas of an image. These tools can highlight a wall in the background and color only that wall, leaving the rest of the frame alone, or color everything but that wall. Subsequent color grading tools (typically software-based) have the ability to use spline-based shapes for even greater control over isolating color adjustments. Color keying is also used for isolating areas to adjust.
Inside and outside of area-based isolations, digital filtration can be applied to soften, sharpen or mimic the effects of traditional glass photographic filters.
When trying to isolate a color adjustment on a moving subject, the colorist traditionally would manually move a mask to follow the subject. In its most simple form, motion tracking software automates this time-consuming process using algorithms to evaluate the motion of a group of pixels. These techniques are generally derived frommatch moving techniques used in special effects and compositing work.
In the 2000s, with the increase of digital technology, color grading in Hollywood films became more common. From 2010, many films, such asHot Tub Time Machine andIron Man 2, began using thecomplementary colors orange and teal.[3]
The evolution of thetelecine device intofilm scanning allowed the digital information scanned from a film negative to be of sufficient resolution to transfer back to film. In the early 1990s, Kodak developed the Cineon Film System to capture, manipulate, and record back to film and they called this the “Digital Intermediate”. This term stuck. The first full digital intermediate of any form was the Cinesite restoration of “Snow White and The Seven Dwarves” in 1993 (previously, in 1990, forRescuers Down Under, the Disney CAPS system had been used to scan artwork, color and composite it, and then record it to film, but this was also intermixed with a traditional lab development process over a length of time).
In the late 1990s, the filmsPleasantville andO Brother, Where Art Thou? advanced the technology to the point that the creation of adigital intermediate was practical, which greatly expanded the capabilities of the digital telecine colorist to the traditionally-oriented world of feature films. Since 2010, almost all feature films have gone through the DI process, while manipulation through photochemical processing is rare or used on archival films.
In Hollywood,O Brother, Where Art Thou? was the first film to be wholly digitally graded. The negative was scanned with aSpirit DataCine at2K resolution, then colors were digitally fine-tuned using a Pandora MegaDef color corrector on aVirtual DataCine. The process took several weeks, and the resultingdigital master was output to film again with a Kodak laserrecorder to create a masterinternegative.
Modern motion picture processing typically uses both digital cameras and digital projectors. Calibrated devices are most commonly used to maintain a consistent appearance within the workflow.
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In early use, hardware-based systems (da Vinci 2K,Pandora International MegaDEF, etc.) have historically offered better performance but a smaller feature set than software-based systems. Their real time performance was optimized to particular resolution and bit depths, as opposed to software platforms using standard computer industry hardware that often trade speed for resolution independence, e.g.Apple's Color (previously Silicon Color Final Touch),ASSIMILATE SCRATCH,Adobe SpeedGrade andSGO Mistika. While hardware-based systems always offer real-time performance, some software-based systems need to pre-render as the complexity of the color grading increases. On the other hand, software-based systems tend to have more features such as spline-based windows/masks and advanced motion tracking.
The line between hardware and software no longer exists as many software-based color correctors (e.g.Pablo,Mistika,SCRATCH,Autodesk Lustre,Nucoda Film Master andFilmLight's Baselight) use multi processor workstations and aGPU (graphics processing unit) as a means ofhardware acceleration. As well, some newer software-based systems use a cluster of multiple parallel GPUs on the one computer system to improve performance at the very high resolutions required for feature film grading. e.g.Blackmagic Design'sDaVinci Resolve. Some color grading software like Synthetic Aperture's Color Finesse runs solely as software and will even run on low-end computer systems. High-speed RAID arrays are an essential part of the process for all systems.
Hardware systems are no longer common because of the price/performance of software systems. The control panels are placed in acolor suite for the colorist to operate the telecine remotely.