The Academy Color Encoding System (ACES) is an image and color management architecture designed primarily for the production, mastering and long-term archiving of motion pictures, although it is being successfully used in television production as well. Developed by the Academy of Motion Picture Arts and Sciences in collaboration with many motion picture production and color science experts, ACES provides a set of digital image encoding specifications, transforms and recommended practices that enable the creation and processing of high fidelity images. It offers a larger dynamic range of scene tones, a wider color gamut and greater mathematical precision than is possible with 10-bit Cineon encoding or High Definition Television standards such as ITU-R Rec. BT.709.


ACES solves a critically urgent need in today’s rapidly evolving digital imaging production and postproduction workflows. 


Consistent color reproduction has become increasingly difficult to manage across multiple image capture/origination and image display platforms and devices. Once upon a time, it was relatively simple to manage color for motion picture production and postproduction because it was based exclusively on photochemical color science within an analog film-based (film negative/film intermediate/film print) workflow.

The transition from traditional film-based photochemical workflow to digital workflows (via hybrid film digital intermediate post finishing) created significant challenges in maintaining consistent color and contrast reproduction. Kodak’s Cineon system pioneered the Digital Intermediate (DI) process to protect the image integrity of film color reproduction within digital workflows by developing (non-video) film scanning, along with carefully crafted print film emulation transforms applied when color grading digitally scanned film images. The color graded images could then be filmed out via a film recorder to make film prints for distribution and/or DCPs (Digital Cinema Package) for digital cinema release. The color graded images were rendered in the color space and gamut of a target output referred display device (e.g., a digital cinema projector) where film print emulation (in the form of a Look Up Table, or LUT) provided the reference for matching digital cinema color reproduction with film prints. Any color and/or tone scale components in the original camera images that fell outside the color gamut and tone scale rendering parameters of the target display device would be clipped. 

A separate color grading pass was then necessary for creating a High Definition (HDTV) master rendered in Rec 709 color space for HDTV and Blu-ray distribution. 

Digital Intermediate also promised a more effective and efficient integration of CGI VFX with live action film image capture, but ensuring consistent reproduction of wide gamut color space, along with extended range tone scale reproduction between CGI and film origination was challenging. Being limited to rendering color graded images within the color gamut and tone scale reproduction capability of digital projection (or monitoring) not only restricted color and dynamic range reproduction, but also the lack of industry standards created variances and vagaries in the transforms used by different post facility implementations of color space. Each facility developed their own "secret sauce” transforms (usually in the form of LUTs {Look Up Tables}) to manage color display reproduction. Even the DPX file format, on which Cineon was based and was standardized through SMPTE, failed to gain strict industry adherence to the written specification. 

The introduction of digital video camera capture into feature film production and post-production workflow added further difficulty in managing consistent color and contrast reproduction when integrated with scanned film and CGI. Different digital cameras introduced different color space and contrast parameters that both derived from and also deviated from the standard Rec 709 HDTV color space/gamut display reference. Things became even more complicated with the relatively recent introduction of digital motion picture cameras that record “RAW” data capture. RAW data capture generally incorporates greater precision of color reproduction (greater bit-depth), a wider color gamut and wider dynamic range of scene tones than HD video cameras. RAW images are also not gamut limited to the capabilities of a specific display device. 

The integration of disparate imaging sources (various digital cameras, scanned film, and VFX) into a final

digital master which does not limit color bit-depth and color fidelity, as well as dynamic range, has been an almost insurmountable challenge.


Why ACES is needed


To protect this expanded color range and wide dynamic range of scene tone reproduction, it is necessary to utilize a color management system that can support images containing greater color bit depth (e.g., the Sony F65 and Sony F55 both output 16-bit color), along with a wide dynamic range of scene tones, within a wide-gamut color space. Also, to more effectively and compatibly integrate these digitally originated images with film origination and film print distribution, ACES incorporates ADX (Academy Density Exchange), a 16-bit film scanning format incorporating a high precision and high dynamic range printing density specification.

ACES image interchange support includes unambiguous transforms between linear and log encoding that enable the introduction of scene (i.e., input) referred color management independent of any prior dependence on rendering to any output device referred color space/gamut and dynamic range. This enables color grading to be rendered within ACES wide gamut color space and then gamut-mapped and dynamic range-mapped to any number of display device specific color spaces.

ACES is the answer to an increasingly urgent industry need for an open, transparent and cross-platform, i.e., device independent, wide gamut color management system. ACES utilizes a standardized wide gamut color encoding, and file format suitable for archiving, that can effectively and efficiently manage disparate color space/color gamut/dynamic range variances of different imaging input sources, in conjunction with different output devices. In addition, ACES provides a future proofing road map that enables current image content to take full advantage of future display devices that support expanded color gamut with greater bit depth, as well as a higher dynamic range of scene tones.

Archiving:

Archival of film was a relatively easy process. The final cut negative was sent to an archive and kept in a temperature and humidity-controlled environment. The negative was archived because that material represented the product in the film chain with the most fidelity and the least compromise. New prints could easily be struck from an archived original negative with reasonable expectation that they would match past prints from the original negative using appropriate printer lights to reproduce the cinematographer’s original creative intent. This was due to the fact that print materials are mostly static photographic media with color science and screen projection parameters that have changed comparatively little from generation to generation.

In the Cineon system the primary archival deliverable was still a film-out negative for the vault.

Alternately, the digital files from the DI were saved, but the usefulness was limited due the ambiguity around which particular viewing LUTs should be used and a lack of film-out standards.

In digital video, the source material is prepared for a specific display device, thereby limiting the ability to remaster the material in the future for new display devices. The archiving of such inherently compromised material is akin to only archiving the print from a film-based production. RAW digital camera files represent a higher level of fidelity, but as they are only a single element of the final movie, they do not have all the necessary components to serve as the digital equivalent of the cut negative in the archive.

ACES files are intended to serve as a high fidelity digital source master for archiving. The archived ACES files contain all composited elements, VFX, and color correction. Viewing archived ACES files is unambiguous with a standardized reference rendering transform. Ambiguities about which LUT should be used to view the images are eliminated.


Summary of ACES benefits:


ACES provides a set of digital image encoding specifications, transforms and recommended practices that enable the creation and processing of high fidelity images. It offers a larger dynamic range of scene tones, a wider color gamut and greater mathematical precision than is possible with 10-bit Cineon encoding or High Definition Television standards such as ITU-R Rec. BT.709.

ACES also resolves ambiguities frequently linked to transforms between so-called “log" and “linear” image encoding, as well as those associated with using a variety of display devices during production, post-production and mastering. ACES supports flexible image pipeline development for many different processes including film and digital acquisition, digital intermediate, visual effects production, remastering and on-set look management.

For cinematographers, ACES provides the following benefits:

• Eliminates uncertainty between on-set look management and downstream color correction through standardized viewing transforms and equipment calibration methods

• Preserves the full range of highlights, shadows and colors captured on-set for use throughout post-production and mastering

• Preserves the ability to use traditional photometric tools for exposure control rather than having to compensate for custom or proprietary viewing transforms in conjunction with video monitoring

• Simplifies matching of images from different camera sources

• Enables future expansion of the creative palette by removing the limitations of legacy workflows

For post-production facilities, ACES provides the following benefits:

• Simplifies interchange of unfinished motion picture materials

• Provides a standard color management platform on which hardware and software vendors can innovate

• Eliminates uncertainty associated with undocumented or poorly documented file formats and color encodings

• Provides a means to repurpose source materials in the creation of alternate deliverables

• Establishes standards for metadata

For visual effects facilities, ACES provides the following benefits:

• Provides well-documented color encodings and file formats based on existing, production tested, technologies such as OpenEXR

• Eliminates the confusion associated with “show LUTs”

• Establishes a common vocabulary and framework for software vendors to provide a consistent color management experience across packages

For producers and studios, ACES provides the following benefits:

• Ensures the archive contains the highest fidelity digital source master possible representing the digital equivalent of the cut negative

• Protects the viability of digital assets by ensuring they can be repurposed to take advantage of future high dynamic range, wide color gamut output devices

Key components and features of ACES include:

• A standardized, fully-specified high-precision, high dynamic range, wide gamut color encoding specification (SMPTE ST2065-1:2012 Academy Color Encoding Specification) encompassing the full range of image color and detail captured by current and future digital cameras

• A standardized, fully-specified high precision and high dynamic range printing density specification (SMPTE ST2065-3:2012 Academy Density Exchange and the related SMPTE ST2065-2:2012 Academy Printing Density) encompassing the full range of image color and detail captured by modern motion picture film stocks

• Standardized file formats for colorimetric and densitometric data based on the popular OpenEXR (SMPTE 2065-4:2013) and DPX data containers (SMPTE 268M-A1)

• A methodology for display device-independent mastering that produces higher quality images than are possible with legacy workflows

• Recommended best-practices for interfacing digital motion picture camera RAW data and film scanner output data to ACES

• A path to an archival digital master that contains the full fidelity of the original image element sources, but in a form which represents the final production

• Support for ASC-CDL in on-set/near-set look management systems. The full benefits of ACES are achieved when cameras, color correctors, image creation and processing tools, and display devices correctly implement the ACES specifications and recommended practices.


For more information about ACES please visit ACESCentral at http://acescentral.com/.