HOME

TheInfoList



OR:

OpenEXR is a high-dynamic range, multi-channel raster
file format A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free. Some file format ...
, released as an
open standard An open standard is a standard that is openly accessible and usable by anyone. It is also a prerequisite to use open license, non-discrimination and extensibility. Typically, anybody can participate in the development. There is no single definitio ...
along with a set of software tools created by
Industrial Light & Magic Industrial Light & Magic (ILM) is an American motion picture visual effects company that was founded on May 26, 1975 by George Lucas. It is a division of the film production company Lucasfilm, which Lucas founded, and was created when he began pr ...
(ILM), under a
free software license A free-software license is a notice that grants the recipient of a piece of software extensive rights to modify and redistribute that software. These actions are usually prohibited by copyright law, but the rights-holder (usually the author) ...
similar to the
BSD license BSD licenses are a family of permissive free software licenses, imposing minimal restrictions on the use and distribution of covered software. This is in contrast to copyleft licenses, which have share-alike requirements. The original BSD lice ...
. It is notable for supporting multiple channels of potentially different pixel sizes, including 32-bit unsigned integer, 32-bit and 16-bit floating point values, as well as various compression techniques which include lossless and
lossy compression In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data si ...
algorithms. It also has arbitrary channels and encodes multiple points of view such as left- and right-camera images.


Overview

A full technical introduction of the format is available on the OpenEXR website. OpenEXR, or EXR for short, is a deep raster format developed by ILM and broadly used in the computer-graphics industry, both visual effects and animation. OpenEXR's multi-resolution and arbitrary channel format makes it appealing for
compositing Compositing is the process or technique of combining visual elements from separate sources into single images, often to create the illusion that all those elements are parts of the same scene. Live action, Live-action shooting for compositing is ...
, as it alleviates several painful elements of the process. Since it can store arbitrary channels— specular, diffuse,
alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whi ...
, RGB, normals, and various other types—in one file, it takes away the need to store this information in separate files. The multi-channel concept also reduces the necessity to "bake" in the aforementioned data to the final image. If a compositer is not happy with the current level of specularity, they can adjust that specific channel. OpenEXR's API makes tools development a relative ease for developers. Since there are almost never two identical production pipelines, custom tools always need to be developed to address problems (e.g. image-manipulation issue). OpenEXR's library allows quick and easy access to the image's attributes such as tiles and channels. The OpenEXR library is developed in
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
and is available in source format as well as compiled format for
Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...
,
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
and
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
. Python bindings for the library are also available for version 2.x.


History

OpenEXR was created by ILM in 1999 and released to the public in 2003 along with an
open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized so ...
software library In computer science, a library is a collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and sub ...
. It soon received wide adoption by software used in
computer graphics Computer graphics deals with generating images with the aid of computers. Today, computer graphics is a core technology in digital photography, film, video games, cell phone and computer displays, and many specialized applications. A great de ...
, particularly for
film A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmospher ...
and
television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, ...
production. The format has been updated several times, adding support for tiles, mipmaps, new compression methods, and other features. In 2007, OpenEXR was honored with an
Academy Award for Technical Achievement The Technical Achievement Award is one of three Scientific and Technical Awards given from time to time by the Academy of Motion Picture Arts and Sciences. (The other two awards are the Scientific and Engineering Award and the Academy Award of Mer ...
. OpenEXR 2.0 was released in April 2013, extending the format with support for deep image buffers and multiple images embedded in a single file. Version 2.2, released August 2014, added the lossy DWA compression format.


Distribution

The OpenEXR software distribution includes: * libraries * Half, a C++ class for manipulating half values as if they were a built-in C++ data type * exrdisplay, a sample application for viewing OpenEXR images on a display at various exposure settings


Libraries

* = library made by
Industrial Light & Magic Industrial Light & Magic (ILM) is an American motion picture visual effects company that was founded on May 26, 1975 by George Lucas. It is a division of the film production company Lucasfilm, which Lucas founded, and was created when he began pr ...
(Ilm) for low-level operations on the files with OpenEXR image format (Imf) ** on linux ** on windows * *


Color depth

OpenEXR has support for
color depth Color depth or colour depth (see spelling differences), also known as bit depth, is either the number of bits used to indicate the color of a single pixel, or the number of bits used for each color component of a single pixel. When referring ...
using: * 16-bit floating-point (half) * 32-bit floating-point * 32-bit unsigned integer


Compression methods

There are three general types of lossless compression built into OpenEXR, with two different methods of Zip compressing. For most images without a lot of grain, the two Zip compression methods seem to work best, while the PIZ compression algorithm is better suited to grainy images. The following options are available: ; None: Disables all compression. ; Run Length Encoding (RLE): This is a basic form of compression that is comparable to that used by standard
Targa Targa or TARGA may refer to: Car racing events *Targa Adelaide, in Australia * Targa Canada West, in British Columbia *Targa Florio, in Sicily, Italy, 1906–1977 * Targa Florio Rally, in Sicily, Italy, from 1978 * Targa High Country, in Victoria ...
files. ; Zip (per scanline): deflate compression with zlib wrapper applied to individual
scanline A scan line (also scanline) is one line, or row, in a raster scanning pattern, such as a line of video on a cathode ray tube (CRT) display of a television set or computer monitor. On CRT screens the horizontal scan lines are visually discernible, ...
s (not based on the
ZIP file format ZIP is an archive file format that supports lossless data compression. A ZIP file may contain one or more files or directories that may have been compressed. The ZIP file format permits a number of compression algorithms, though DEFLATE is th ...
despite its name). ; Zip (16 scanline blocks): deflate compression applied to blocks of 16 scanlines at time. This tends to be the most effective style of compression to use with rendered images that do not have film grain applied. ; PIZ (
wavelet A wavelet is a wave-like oscillation with an amplitude that begins at zero, increases or decreases, and then returns to zero one or more times. Wavelets are termed a "brief oscillation". A taxonomy of wavelets has been established, based on the num ...
compression): This lossless method uses a new combined wavelet / Huffman compression. This form of compression is quite effective when dealing with grainy images, and will often surpass any of the other options under grainy conditions. ; PXR24 (24-bit data conversion then deflate compression): This form of compression from
Pixar Animation Studios Pixar Animation Studios (commonly known as Pixar () and stylized as P I X A R) is an American computer animation studio known for its critically and commercially successful computer animated feature films. It is based in Emeryville, Califor ...
converts 32-bit floats to 24 bits then uses deflate compression. It is lossless for half and 32-bit integer data and slightly lossy for 32-bit float data. ; B44: This form of compression is lossy for half data and stores 32-bit data uncompressed. It maintains a fixed compression size of either 2.28:1 or 4.57:1 and is designed for realtime playback. B44 compresses uniformly regardless of image content. ; B44A: An extension to B44 where areas of flat color are further compressed, such as alpha channels. ; DWAA: JPEG-like lossy compression format contributed by
DreamWorks Animation DreamWorks Animation LLC (DWA, also known as DreamWorks Animation Studios and simply known as DreamWorks) is an American animation studio that produces animated films and television programs and is a subsidiary of Universal Pictures, a divisio ...
. Compresses 32 scanlines together. ; DWAB: Same as DWAA, but compresses blocks of 256 scanlines.


Credits

From OpenEXR.org's Technical Introduction:
The ILM OpenEXR file format was designed and implemented by Florian Kainz, Wojciech Jarosz, and Rod Bogart. The PIZ compression scheme is based on an algorithm by Christian Rouet. Josh Pines helped extend the PIZ algorithm for 16-bit and found optimizations for the float-to-half conversions. Drew Hess packaged and adapted ILM's internal source code for public release and maintains the OpenEXR software distribution. The PXR24 compression method is based on an algorithm written by Loren Carpenter at Pixar Animation Studios.


See also

*
High dynamic range High dynamic range (HDR) is a dynamic range higher than usual, synonyms are wide dynamic range, extended dynamic range, expanded dynamic range. The term is often used in discussing the dynamic range of various signals such as images, videos, au ...


References


External links

*
exrtools incl. exrtoppm exe
{{Graphics file formats Free graphics software High dynamic range High dynamic range file formats Lucasfilm Open formats Raster graphics file formats Software using the BSD license