It has been suggested that Free-software community be merged into this article or section. (Discuss) Proposed since December 2011.

Free software

While most GNU/Linux distributions are composed almost entirely[1] of free software, only a minority of them, such as Trisquel, meet the FSF's strict guidelines by completely eschewing proprietary components.[2]

Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients have the same rights under which it was obtained and that manufacturers of consumer products incorporating free software provide the software as source code. The word free in the term free software refers to freedom (liberty) and is not at all related to monetary cost. The Free Software Foundation advises people to "avoid using terms like 'give away' or 'for free,' because those terms imply that the issue is about price, not freedom."^[3] Free software is generally available without charge but is not bound to such a restriction.

Fees are usually charged for distribution on compact discs and bootable USB drives, or for services of installing or maintaining the operation of free software. Development of large, commercially-used free software is often funded by a combination of user donations, corporate contributions, and tax money. The SELinux project at the United States National Security Agency is an example of a federally-funded free software project.

In practice, for software to be distributed as free software, the source code, a human-readable form of the program from which an executable form is produced, must be accessible to the recipient along with a document granting the same rights to free software under which it was published. Such a document is either a free software license or the release of the source code into the public domain.

The free software movement was conceived in 1983 by Richard Stallman to satisfy the need for and to give the benefit of software freedom to computer users.^[4] Stallman founded the Free Software Foundation in 1985 to provide the organizational structure to advance his free software ideas.

From 1998 onward, alternative terms for free software came into use. The most common are software libre, free and open source software (FOSS) and free, libre and open source software (FLOSS). The Software Freedom Law Center was founded in 2005 to protect and advance FLOSS.^[5] Commercial software may sometimes offer freedoms which are typical of free and open source software. Contrary to a popular misconception that software is either free or commercial, they are unrelated traits, since free software can be commercial and proprietary software can be non-commercial. One example of free commercial software is GNAT, an Ada compiler from the company AdaCore.^[6] It has been developed and is available commercially (i.e., against payment), but is free software because of its non-proprietary nature, with the source code publicly available. On the other hand, free software and proprietary software are opposite traits, and an application can be one or the other but never both, contingent upon the availability of the source code under certain minimum freedoms.

Free software, which may or may not be distributed free of charge, is distinct from freeware, which by definition does not require payment for use. The authors or copyright holders of freeware may retain all rights to the software; it is not necessarily permissible to reverse engineer, modify, or redistribute freeware.^[7][8]

Since free software may be freely redistributed, it is generally available at little or no cost. Free software business models are usually based on adding value such as applications, support, training, customization, integration, or certification. At the same time, some business models which work with proprietary software are not compatible with free software, such as those that depend on the user to pay for a license in order to lawfully use the software product.

History[link]

Richard Stallman, the founder of the Free Software Movement

In the 1950s, 1960s, and until the early 1970s, it was normal for computer users to have the software freedoms associated with free software. Software was commonly shared by individuals who used computers and by hardware manufacturers who welcomed the fact that people were making software that made their hardware useful. Organizations of users and suppliers, for example, SHARE, were formed to facilitate exchange of software. By the early 1970s, the picture changed: software costs were dramatically increasing, a growing software industry was competing with the hardware manufacturer's bundled software products (free in that the cost was included in the hardware cost), leased machines required software support while providing no revenue for software, and some customers able to better meet their own needs did not want the costs of "free" software bundled with hardware product costs. In United States vs. IBM, filed January 17, 1969, the government charged that bundled software was anticompetitive.^[9] While some software might always be free, there would be a growing amount of software that was for sale only. In the 1970s and early 1980s, the software industry began using technical measures (such as only distributing binary copies of computer programs) to prevent computer users from being able to study and modify software. In 1980 copyright law was extended to computer programs.

In 1983, Richard Stallman, longtime member of the hacker community at the MIT Artificial Intelligence Laboratory, announced the GNU project, saying that he had become frustrated with the effects of the change in culture of the computer industry and its users. Software development for the GNU operating system began in January 1984, and the Free Software Foundation (FSF) was founded in October 1985. He developed a free software definition and the concept of "copyleft", designed to ensure software freedom for all.

Some non-software industries are beginning to use techniques similar to those used in free software development for their research and development process; scientists, for example, are looking towards more open development processes, and hardware such as microchips are beginning to be developed with specifications released under copyleft licenses (see the OpenCores project, for instance). Creative Commons and the free culture movement have also been largely influenced by the free software movement.

Naming[link]

The FSF recommends using the term "free software" rather than "open source software" because, as they state in a paper on Free Software philosophy, the latter term and the associated marketing campaign focuses on the technical issues of software development, avoiding the issue of user freedoms. The FSF also notes that "Open Source" has exactly one specific meaning in common English, namely that "[y]ou can look at the source code." Stallman states that while the term "Free Software" can lead to two different interpretations, one of them is consistent with FSF definition of Free Software so there is at least some chance that it could be understood properly, unlike the term "Open Source".^[10] "Libre" is often used to avoid the ambiguity of the word "free" in English language; see Gratis versus libre.

Definition[link]

The first formal definition of free software was published by FSF in February 1986.^[11] That definition, written by Richard Stallman, is still maintained today and states that software is free software if people who receive a copy of the software have the following four freedoms.^[12] (The numbering begins with zero since many computer systems use zero-based numbering.)

• Freedom 0: The freedom to run the program for any purpose.
• Freedom 1: The freedom to study how the program works, and change it to make it do what you wish.
• Freedom 2: The freedom to redistribute copies so you can help your neighbor.
• Freedom 3: The freedom to improve the program, and release your improvements (and modified versions in general) to the public, so that the whole community benefits.

Freedoms 1 and 3 require source code to be available because studying and modifying software without its source code is highly impractical.

Thus, free software means that computer users have the freedom to cooperate with whom they choose, and to control the software they use. To summarize this into a remark distinguishing libre (freedom) software from gratis (zero price) software, the Free Software Foundation says: "Free software is a matter of liberty, not price. To understand the concept, you should think of 'free' as in 'free speech', not as in 'free beer'".^[13] See Gratis versus libre.

In the late 1990s, other groups published their own definitions which describe an almost identical set of software. The most notable are Debian Free Software Guidelines published in 1997,^[14] and the Open Source Definition, published in 1998.

The BSD-based operating systems, such as FreeBSD, OpenBSD, and NetBSD, do not have their own formal definitions of free software. Users of these systems generally find the same set of software to be acceptable, but sometimes see copyleft as restrictive. They generally advocate permissive free software licenses, which allow others to use the software as they wish, without being legally forced to provide the source code. Their view is that this permissive approach is more free. The Kerberos, X11, and Apache software licenses are substantially similar in intent and implementation.

Examples of free software[link]

The Free Software Directory maintains a large database of free software packages. Some of the best-known examples include the Linux Kernel, the BSD and GNU/Linux operating systems, the GNU Compiler Collection and C library; the MySQL relational database; the Apache web server; and the Sendmail mail transport agent. Other influential examples include the emacs text editor; the GIMP raster drawing and image editor; the X Window System graphical-display system; the LibreOffice office suite; and the TeX and LaTeX typesetting systems.

Free software licenses[link]

All free software licenses must grant users all the freedoms discussed above. However, unless the applications' licenses are compatible, combining programs by mixing source code or directly linking binaries is problematic, because of license technicalities. Programs indirectly connected together may avoid this problem.

The majority of free software falls under a small set of licenses. The most popular of these licenses are:

• the GNU General Public License
• the GNU Lesser General Public License
• the BSD License
• the Mozilla Public License
• the MIT License
• the Apache License

The Free Software Foundation and the Open Source Initiative both publish lists of licenses that they find to comply with their own definitions of free software and open-source software respectively.

• List of FSF approved software licenses
• List of OSI approved software licenses

The FSF list is not prescriptive: free licenses can exist which the FSF has not heard about, or considered important enough to write about. So it's possible for a license to be free and not in the FSF list. The OSI list only lists licenses that have been submitted, considered and approved. All Open Source licenses must meet the Open Source Definition in order to be officially recognized as open source software. Free software on the other hand is a more informal classification that does not rely on official recognition. Nevertheless, software licensed under licenses that do not meet the Free Software Definition cannot rightly be considered free software.

Apart from these two organizations, the Debian project is seen by some to provide useful advice on whether particular licenses comply with their Debian Free Software Guidelines. Debian doesn't publish a list of approved licenses, so its judgments have to be tracked by checking what software they have allowed into their software archives. That is summarized at the Debian web site.^[15]

It is rare that a license announced as being in-compliance with the FSF guidelines does not also meet the Open Source Definition, although the reverse is not necessarily true (for example, the NASA Open Source Agreement is an OSI-approved license, but non-free according to FSF).

Different types of licenses[link]

There are different categories of free software.

• Public domain software – the copyright has expired, the work was not copyrighted, or the author has released the software onto the public domain (in countries where this is possible). Since public-domain software lacks copyright protection, it may be freely incorporated into any work, whether proprietary or free.
• Permissive licenses, also called BSD-style because they are applied to much of the software distributed with the BSD operating systems. These licenses are also known as copyfree as they have no restrictions on distribution.^[16] The author retains copyright solely to disclaim warranty and require proper attribution of modified works, and permits redistribution and any modification, even closed source ones.
• Copyleft licenses, with the GNU General Public License being the most prominent. The author retains copyright and permits redistribution under the restriction that all such redistribution is licensed under the same license. Additions and modifications by others must also be licensed under the same "copyleft" license whenever they are distributed with part of the original licensed product. This is also known as a Viral license. Due to the restriction on distribution not everyone considers this type of license to be free.^{[17][18][19][20]}

Security and reliability[link]

There is debate over the security of free software in comparison to proprietary software, with a major issue being security through obscurity. A popular quantitative test in computer security is to use relative counting of known unpatched security flaws. Generally, users of this method advise avoiding products which lack fixes for known security flaws, at least until a fix is available.

Free software advocates say that this method is biased by counting more vulnerabilities for the free software, since its source code is accessible and its community is more forthcoming about what problems exist,^[21] (This is called "Security Through Disclosure"^[22]) and proprietary software can have undisclosed flaws discoverable by or known to malicious users. As users can analyse and trace the source code, many more people with no commercial constraints can inspect the code and find bugs and loopholes than a corporation would find practicable. According to Richard Stallman, user access to the source code makes deploying free software with undesirable hidden spyware functionality far more difficult than for proprietary software.^[23] As examples, he named two aspects of Windows XP that reveal information to Microsoft, which were discovered in spite of the estimated 50 million or more lines of Windows code having not been available to individual users for personal auditing.

Some quantitative studies have been done on the subject.^[24][25]

Selling free software[link]

Selling Software under the BSD license is permissible and commercial use of the project is part of the intent of the license.^[26][27]

The Free Software Foundation encourages selling free software. As the Foundation has written, "Distributing free software is an opportunity to raise funds for development. Don't waste it!".^[28] For example the GNU GPL which is the Free Software Foundation's license states that "[the user] may charge any price or no price for each copy that you convey, and you may offer support or warranty protection for a fee."^[29]

It is a common misbelief however that consumers shouldn't or aren't allowed to redistribute software under the GPL for profit,^{[citation needed]} and some opposing parties state such notions. For example Microsoft CEO Steve Ballmer stated in 2001 that "Open source is not available to commercial companies. The way the license is written, if you use any open-source software, you have to make the rest of your software open source."^[30] When you distribute software under the GPL, you must provide the source code as well and must allow others to distribute it. Yet there are large companies, e.g. Red Hat and IBM, which succeed in doing it.

Economical aspects and adoption[link]

Free software played a significant part in the development of the Internet, the World Wide Web and the infrastructure of dot-com companies.^[31][32] Free software allows users to cooperate in enhancing and refining the programs they use; free software is a pure public good rather than a private good. Companies that contribute to free software can increase commercial innovation amidst the void of patent cross licensing lawsuits.^{[citation needed]} (See mpeg2 patent holders.)

The economic viability of free software has been recognized by large corporations such as IBM, Red Hat, and Sun Microsystems.^{[33][34][35][36][37]} Many companies whose core business is not in the IT sector choose free software for their Internet information and sales sites, due to the lower initial capital investment and ability to freely customize the application packages.

Under the free software business model^{[further explanation needed]}, free software vendors may charge a fee for distribution and offer pay support and software customization services. Proprietary software uses a different business model, where a customer of the proprietary software pays a fee for a license to use the software. This license may grant the customer the ability to configure some or no parts of the software themselves. Often some level of support is included in the purchase of proprietary software, but additional support services (especially for enterprise applications) are usually available for an additional fee. Some proprietary software vendors will also customize software for a fee.^[38]

Free software is generally available at no cost and can result in permanently lower TCO costs compared to proprietary software.^[39] With free software, businesses can fit software to their specific needs by changing the software themselves or by hiring programmers to modify it for them. Free software often has no warranty, and more importantly, generally does not assign legal liability to anyone. However, warranties are permitted between any two parties upon the condition of the software and its usage. Such an agreement is made separately from the free software license.

A report by Standish Group estimates that adoption of free software has caused a drop in revenue to the proprietary software industry by about $60 billion per year.^[40]

Controversies[link]

Binary blobs[link]

In 2006, OpenBSD started the first campaign against the use of binary blobs, in kernels. Blobs are usually freely distributable device drivers for hardware from vendors that do not reveal driver source code to users or developers. This restricts the users' freedom effectively to modify the software and distribute modified versions. Also, since the blobs are undocumented and may have bugs, they pose a security risk to any operating system whose kernel includes them. The proclaimed aim of the campaign against blobs is to collect hardware documentation that allows developers to write free software drivers for that hardware, ultimately enabling all free operating systems to become or remain blob-free.

The issue of binary blobs in the Linux kernel and other device drivers motivated some developers in Ireland to launch gNewSense, a GNU/Linux based distribution with all the binary blobs removed. The project received support from the Free Software Foundation and stimulated the creation, headed by the Free Software Foundation Latin America, of the Linux-libre kernel.^[41] The project has since been classified dormant by Distrowatch.^[42] As of 2012, Trisquel is the most popular FSF endorsed GNU/Linux distribution ranked by Distrowatch. ^[43]

BitKeeper[link]

Larry McVoy invited high-profile free software projects to use his proprietary distributed version control system, BitKeeper, free of charge, in order to attract paying users. In 2002, Linux coordinator Linus Torvalds decided to use BitKeeper to develop the Linux kernel, a free software project, claiming no free software alternative met his needs. This controversial decision drew criticism from several sources, including the Free Software Foundation's founder Richard Stallman.^[44]

Following the apparent reverse engineering of BitKeeper's protocols, McVoy withdrew permission for gratis use by free software projects. Linus Torvalds quickly developed a free software replacement called Git, while fellow Linux kernel contributor Matt Mackall developed another free software replacement called Mercurial. The Linux kernel eventually settled on Git for its own development process, while some other free software projects have chosen Mercurial.

Patent deals[link]

In November 2006, the Microsoft and Novell software corporations announced a controversial partnership involving, among other things, patent protection for some customers of Novell under certain conditions.^[45] FSF included as a result of this deal conditions in the GPL to prevent deals like it in the future.^[46]

Criticism[link]

Eric S. Raymond argues that the term free software is too ambiguous and intimidating for the business community. Raymond promotes the term open source software as a more friendly alternative for the business and corporate world.^[47]

See also[link]

	Free software portal
	Software portal

Lists[link]

References[link]

Books and articles[link]

• Puckette, Miller. “Who Owns our Software?: A first-person case study.” eContact! 11.3 — Logiciels audio « open source » / Open Source for Audio Application^{[dead link]} (September 2009). Montréal: CEC.
• Hancock, Terry. "The Jargon of Freedom: 60 Words and Phrases with Context" Free Software Magazine. 2010-20-24
• Stallman, Richard M. (2002). Free software, free society: Selected Essays of Richard M. Stallman. GNU Press. ISBN 978-1-882114-98-6. http://www.gnu.org/philosophy/fsfs/rms-essays.pdf. 

External links[link]

Wikimedia Commons has media related to: Free software

Wikinews has news related to: FLOSS

• The Free Software Definition
• Software Freedom Law Center
• Free Software Definition at The Linux Information Project
• Donation Central: a directory listing the donation pages of various Free software projects.

This article may require copy editing for grammar and tense. You can assist by editing it. (August 2011)

Today's practicality of green screen compositing is demonstrated by Iman Crosson in a self-produced YouTube video.
Top panel: A frame of Crosson in a full motion video that was shot in his own living room.
Bottom panel: The corresponding frame in the final version, in which Crosson, impersonating Barack Obama, "appears" in the White House's East Room.^[1]

Chroma key compositing, or chroma keying, is a special effects / post-production technique for compositing (layering) two images or video streams together, used heavily in many fields to remove a background from the subject of a photo or video - particularly the newscasting, motion picture and videogame industries. A color range in the top layer is made transparent, revealing another image behind. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as color keying, colour-separation overlay (CSO; primarily by the BBC^[2]), or by various terms for specific color-related variants such as green screen, and blue screen - chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most human skin colors and no part of the subject being filmed or photographed may duplicate a color used in the background.^[3] It is commonly used for weather forecast broadcasts, wherein the news presenter appears to be standing in front of a large map during live television newscasts, though in actuality it is a large blue or green background. When using a blue screen, different weather maps are added on the parts of the image where the color is blue. If the news presenter wears blue clothes, his clothes will also be replaced with the background video. A complementary system is used for green screens. Chroma keying is also used in the entertainment industry for special effects in movies and videogames. The advanced state of the technology and much commercially available computer software, such as Pinnacle Studio, Adobe Premiere, and dozens of other computer programs, makes it possible and relatively easy for the average home computer user to create videos using the "chromakey" function and easily affordable greenscreen or bluescreen kits.

History[link]

In filmmaking, a complex and time-consuming process known as "travelling matte" was used prior to the introduction of digital compositing. The blue screen and traveling matte method were developed in the 1930s at RKO Radio Pictures and other studios, and were used to create special effects for The Thief of Bagdad (1940). At RKO, Linwood Dunn used a travelling matte to create "wipes" – where there were transitions like a windshield wiper in films such as Flying Down to Rio (1933).

The development of the bluescreen is credited to Larry Butler, who won the Academy Award for special effects for The Thief of Bagdad.

In 1950, Warner Brothers employee and ex-Kodak researcher Arthur Widmer began working on an ultra violet travelling matte process. He also began developing bluescreen techniques: one of the first films to use them was the 1958 adaptation of the Ernest Hemingway novella, The Old Man and the Sea, starring Spencer Tracy.^[4]

The background footage is shot first and the actor or model is filmed carrying out their actions against a bluescreen. To simply place the foreground shot over the background shot would create a ghostly image over a blue-tinged background. The actor or model must be separated from the background and placed into a specially-made "hole" in the background footage. The bluescreen shot was first rephotographed through a blue filter so that only the background is exposed. A special film is used that creates a black and white negative image — a black background with a subject-shaped hole in the middle. This is called a 'female matte'. The bluescreen shot was then rephotographed again, this time through a red and green filter so that only the foreground image was cast on film, creating a black silhouette on an unexposed (clear) background. This is called a 'male matte'.

The background image is then rephotographed through the male matte, and the shot rephotographed through the female matte. An optical printer with two projectors, a film camera and a 'beam splitter' combines the images together one frame at a time. This part of the process must be very carefully controlled to ensure the absence of 'black lines'. During the 1980s, minicomputers were used to control the optical printer. For The Empire Strikes Back, Richard Edlund created a 'quad optical printer' that accelerated the process considerably and saved money. He received a special Academy Award for his innovation.

One drawback to the traditional traveling matte is that the cameras shooting the images to be composited can't be easily synchronized. For decades, such matte shots had to be done "locked-down" so that neither the matted subject nor the background could shift their camera perspective at all. Later, computer-timed motion control cameras alleviated this problem, as both the foreground and background could be filmed with the same camera moves.

Petro Vlahos was awarded an Academy Award for his development of these techniques. His technique exploits the fact that most objects in real-world scenes have a color whose blue color component is similar in intensity to their green color component. Zbigniew Rybczyński also contributed to bluescreen technology.

For Star Trek: The Next Generation, an ultraviolet light matting process was proposed by Don Lee of CIS and developed by Gary Hutzel and the staff of Image G. This involved a fluorescent orange backdrop which made it easier to generate a holdout matte, thus allowing the effects team to produce effects in a quarter of the time needed for other methods.^[5]

Some films make heavy use of chroma key to add backgrounds that are constructed entirely using computer-generated imagery (CGI). Performances from different takes can even be composited together, which allows actors to be filmed separately and then placed together in the same scene. Chroma key allows performers to appear to be in any location without even leaving the studio.

Computer development also made it easier to incorporate motion into composited shots, even when using handheld cameras. Reference-points can now be placed onto the colored background (usually as a painted grid, X's marked with tape, or equally spaced tennis balls attached to the wall). In post-production, a computer can use the references to adjust the position of the background, making it match the movement of the foreground perfectly. Modern advances in software and computational power have even eliminated the need to use grids or tracking marks – the software analyzes the relative motion of colored pixels against other colored pixels and solves the 'motion' to create a camera motion algorithm which can be used in compositing software to match the motion of composited elements to a moving background plate.

Weathermen often use a field monitor to the side of the screen to see where they are putting their hands. A newer technique is to project a faint image onto the screen.

Process[link]

Film set for The Spiderwick Chronicles, where a special effects scene using bluescreen chroma key is in preparation.

The principal subject is filmed or photographed against a background consisting of a single color or a relatively narrow range of colors, usually blue or green because these colors are considered to be the furthest away from skin tone.^[3] The portions of the video which match the preselected color are replaced by the alternate background video. This process is commonly known as "keying", "keying out" or simply a "key".

Green is currently used as a backdrop more than any other color because image sensors in digital video cameras are most sensitive to green, due to the bayer pattern allocating more pixels to the green channel, mimicking the human eye's increased sensitivity to green light.^[6] Therefore, the green camera channel contains the least "noise" and can produce the cleanest key/matte/mask. Additionally, less light is needed to illuminate green, again because of the higher sensitivity to green in image sensors.^[7] Bright green has also become favored as a blue background may match a subject's eye color or common items of clothing, such as jeans, or a dark-navy suit.

Blue was used before digital keying became commonplace because it was necessary for the optical process, but it needed more illumination than green. However, it is also further in the visual spectrum from red, the predominant color in human skin.

The most important factor for a key is the color separation of the foreground (the subject) and background (the screen) – a bluescreen will be used if the subject is predominately green (for example plants), despite the camera being more sensitive to green light.

In analog color TV, color is represented by the phase of the chroma subcarrier relative to a reference oscillator. Chroma key is achieved by comparing the phase of the video to the phase corresponding to the preselected color. In-phase portions of the video are replaced by the alternate background video.

In digital color TV, color is represented by three numbers (red, green, blue). Chroma key is achieved by a simple numerical comparison between the video and the preselected color. If the color at a particular point on the screen matches (either exactly, or in a range), then the video at that point is replaced by the alternate background video.

Clothing[link]

A chroma key subject must not wear clothing similar in color to the chroma key color(s) (unless intentional), because the clothing may be replaced with the background video. An example of intentional use of this is when an actor wears a blue covering over a part of his body to make it invisible in the final shot. This technique can be used to achieve an effect similar to that used in the Harry Potter films to create the effect of an invisibility cloak. The actor can also be filmed against a chroma key background and inserted into the background shot with a distortion effect in order to create a cloak that is marginally detectable.^[8]

Difficulties emerge with bluescreen when a costume in an effects shot must be blue, such as Superman's traditional blue outfit. In the 2002 film Spider-Man, in scenes where both Spider-Man and the Green Goblin are in the air, Spider-Man had to be shot in front of the greenscreen and the Green Goblin had to be shot in front of a bluescreen, because Spider-Man wears a costume which is red and blue in color and the goblin wears a costume which is entirely green in color. If both were shot in front of the same screen, one character would have been partially erased from the shot.

Background[link]

Demonstration of the creation of special effects techniques utilizing chroma key.

Blue is generally used for both weather maps and special effects because it is complementary to human skin tone. The use of blue is also tied to the fact that the blue emulsion layer of film has the finest crystals and thus good detail and minimal grain (in comparison to the red and green layers of the emulsion.) In the digital world, however, green has become the favored color because digital cameras retain more detail in the green channel and it requires less light than blue. Green not only has a higher luminance value than blue but also in early digital formats the green channel was sampled twice as often as the blue, making it easier to work with. The choice of color is up to the effects artists and the needs of the specific shot. In the past decade, the use of green has become dominant in film special effects. Also, the green background is favored over blue for outdoors filming where the blue sky might appear in the frame and could accidentally be replaced in the process. Although green and blue are the most common, any color can be used. Red is usually avoided due to its prevalence in normal human skin pigments, but can be often used for objects and scenes which do not involve people.

Occasionally, a magenta background is used, as in some software applications where the magenta or fuchsia key value #FF00FF is sometimes referred to as "magic pink".^[9]

With better imaging and hardware, many companies are avoiding the confusion often experienced by weather presenters, who must otherwise watch themselves on a monitor to see the image shown behind them, by lightly projecting a copy of the background image onto the blue/green screen. This allows the presenter to accurately point and look at the map without referring to monitors.

A newer technique is to use a retroreflective curtain in the background, along with a ring of bright LEDs around the camera lens. This requires no light to shine on the background other than the LEDs, which use an extremely small amount of power and space unlike big stage lights, and require no rigging. This advance was made possible by the invention of practical blue LEDs in the 1990s, which also allow for emerald green LEDs.

There is also a form of color keying that uses light spectrum invisible to human eye. Called Thermo-Key, it uses infrared as the key color, which would not be replaced by background image during postprocessing.^[10][11]

Even lighting[link]

The biggest challenge when setting up a bluescreen or greenscreen is even lighting and the avoidance of shadow, because it is best to have as narrow a color range as possible being replaced. A shadow would present itself as a darker color to the camera and might not register for replacement. This can sometimes be seen in low-budget or live broadcasts where the errors cannot be manually repaired. The material being used affects the quality and ease of having it evenly lit. Materials which are shiny will be far less successful than those that are not. A shiny surface will have areas that reflect the lights making them appear pale, while other areas may be darkened. A matte surface will diffuse the reflected light and have a more even color range. In order to get the cleanest key from shooting greenscreen it is necessary to create a value difference between the subject and the greenscreen. In order to differentiate the subject and screen a two-stop difference can be used, either by making the greenscreen two stops higher than the subject or vice versa.

Sometimes a shadow can be used to create a special effect. Areas of the bluescreen or greenscreen with a shadow on them can be replaced with a darker version of the desired background video image, making it look like the person casting the shadow is actually casting a shadow on the background image instead.

Another common, related, problem is lighting the subjects in a manner that is complementary to the scene being keyed in behind. Attention has to be paid to matching the direction of lighting and the color balance in the background. Any spill of the chroma key color will make the result look unnatural. Even a difference in the focal length of the lenses used can affect the success of chroma key.

Exposure[link]

Another challenge for bluescreen or greenscreen is proper camera exposure. Underexposing or overexposing a colored backdrop can lead to poor saturation levels. In the case of video and digital cinema cameras, underexposed images can contain high amounts of noise, as well. The background must be bright enough to allow the camera to create a bright and saturated image.

Programming[link]

There are several different quality- and speed-optimized techniques for implementing color keying in software.^[12]

In most versions, a function f(r, g, b) → α is applied to every pixel in the image. α (alpha) has a meaning similar to that in alpha compositing techniques. α ≤ 0 means the pixel is the green screen, α ≥ 1 means the pixel is in the foreground object. Values between 0 and 1 indicate a pixel that is partially covered by the foreground object. A usable green screen example, which matches how chroma key was done on an optical printer, is f(r, g, b) = K₀ * b − K₁ * g + K₂ (K_0..2 are user-adjustable constants, 1 is a good initial guess for all of them).

Often the software does screen spill removal from the colors as well as figure out the alpha. This may be a separate function g(r, g, b) → (r, g, b), a very simple green screen example is g(r, g, b) → (r, min(g, b), b). Or f is changed to return (r, g, b, a) all at once, this is useful if part of the calculation is shared.

Most keyers use far more complicated functions. A popular approach is to describe a closed 3D surface in RGB space and determine the signed distance the point (r, g, b) is from this surface, or to find the distance the point (r, g, b) is between two closed nested surfaces. It is also very common for f() to depend on more than just the current pixel's color, it may also use the (x, y) position, the values of nearby pixels, the value from reference images, and values from user-drawn masks.

A different class of algorithm tries to figure out a 2D path that separates the foreground from the background. This path can be the output, or the image can be drawn by filling the path with α = 1 as a final step. An example of such an algorithm is the use of active contour. Most research in recent years has been into these algorithms.

See also[link]

• Compositing
• Federal Standard 1037C
• Filmmaking
• Drew Carey's Green Screen Show
• Film production
• Front projection effect
• Live action
• Matte (filmmaking)
• Muslin
• Optical printer
• Primatte chromakey technology
• Rear projection effect
• Reverse bluescreen
• Schüfftan process
• Signal processing
• Sodium vapor process
• Special effects
• Video switcher
• Virtual set

References[link]

External links[link]

• Building a Chroma Key on a low budget (Google Knol)
• How Blue Screens Work
• Stargate Studios Virtual Backlot Reel 2012 -- An awesome demonstration of green screen work!!!

Richard Matthew Stallman
Richard Stallman at the University of Pittsburgh 2010
Born	(1953-03-16) March 16, 1953 (age 59) New York City, New York, United States
Nationality	American
Other names	rms, St. iGNUcius (avatar)
Alma mater	Harvard University Massachusetts Institute of Technology
Occupation	President of the Free Software Foundation
Known for	Free software movement, GNU, Emacs
Website
www.stallman.org

Richard Matthew Stallman (born 16 March 1953), often shortened to rms,^[1] is an American software freedom activist and computer programmer. In September 1983, he launched the GNU Project^[2] to create a free Unix-like operating system, and he has been the project's lead architect and organizer. With the launch of the GNU Project, he initiated the free software movement; in October 1985^[3] he founded the Free Software Foundation.

Stallman pioneered the concept of copyleft, and he is the main author of several copyleft licenses including the GNU General Public License, the most widely used free software license.^[4] Since the mid-1990s, Stallman has spent most of his time advocating for free software, as well as campaigning against software patents, digital rights management, and what he sees as excessive extension of copyright laws. Stallman has also developed a number of pieces of widely used software, including the original Emacs,^[5] the GNU Compiler Collection,^[6] the GNU Debugger,^[7] and various tools in the GNU coreutils.^[8] He co-founded the League for Programming Freedom in 1989.

Early years[link]

Stallman was born to Daniel Stallman and Alice Lippman,^[9] in 1953 in New York City. His first experience with computers was at the IBM New York Scientific Center when he was in high school. He was hired for the summer to write a numerical analysis program in Fortran. He completed the task after a couple of weeks and spent the rest of the summer writing a text editor in APL.^[10] Stallman spent the summer after his high-school graduation writing another program, a preprocessor for the PL/I programming language on the IBM System/360.^{[citation needed]}

During this time, Stallman was also a volunteer laboratory assistant in the biology department at Rockefeller University. Although he was already moving toward a career in mathematics or physics, his teaching professor at Rockefeller thought he would have a future as a biologist.^[11]

As a first-year student at Harvard University, Stallman was known for his strong performance in Math 55.^{[citation needed]} In 1971 he became a programmer at the MIT Artificial Intelligence Laboratory, and became a regular in the hacker community, where he was usually known by his initials, rms (which was the name of his computer accounts). In the first edition of the Hacker's Dictionary, he wrote "'Richard Stallman' is just my mundane name; you can call me 'rms'."^[1] Stallman graduated from Harvard magna cum laude earning a BA in Physics in 1974.^[12]

Stallman enrolled as a graduate student at MIT, but then ended his pursuit of a doctorate in physics to focus on his programming at the MIT AI Laboratory.

While a graduate student at MIT, Stallman published a paper with Gerald Jay Sussman on an AI truth maintenance system, called dependency-directed backtracking.^[13] This paper was an early work on the problem of intelligent backtracking in constraint satisfaction problems. As of 2003, the technique Stallman and Sussman introduced is still the most general and powerful form of intelligent backtracking.^[14] The technique of constraint recording, wherein partial results of a search are recorded for later reuse, was also introduced in this paper.^[14]

As a hacker in MIT's AI laboratory, Stallman worked on software projects like TECO, Emacs, and the Lisp machine Operating System. He would become an ardent critic of restricted computer access in the lab, which at that time was funded primarily by the Defense Advanced Research Projects Agency. When MIT's Laboratory for Computer Science (LCS) installed a password control system in 1977, Stallman found a way to decrypt the passwords and sent users messages containing their decoded password, with a suggestion to change it to the empty string (that is, no password) instead, to re-enable anonymous access to the systems. Around 20% of the users followed his advice at the time, although passwords ultimately prevailed. Stallman boasted of the success of his campaign for many years afterward.^[15]

Decline of MIT's hacker culture[link]

In the late 1970s and early 1980s, the hacker culture that Stallman thrived on began to fragment. To prevent software from being used on their competitors' computers, most manufacturers stopped distributing source code and began using copyright and restrictive software licenses to limit or prohibit copying and redistribution. Such proprietary software had existed before, and it became apparent that it would become the norm. This shift in the legal characteristics of software can be regarded as a consequence triggered by the U.S. Copyright Act of 1976, as stated by Stallman's MIT fellow Brewster Kahle.^[16]

When Brian Reid in 1979 placed time bombs in the Scribe markup language and word processing system to restrict unlicensed access to the software, Stallman proclaimed it "a crime against humanity."^[17] He clarified, years later, that it is blocking the user's freedom that he believes is a crime, not the issue of charging for the software.^[18]

In 1980, Stallman and some other hackers at the AI Lab were refused access to the source code for the software of a newly-installed laser printer, the Xerox 9700. Stallman had modified the software for the Lab's previous laser printer (the XGP, Xerographic Printer), so it electronically messaged a user when the person's job was printed, and would message all logged-in users waiting for print jobs if the printer was jammed. Not being able to add these features to the new printer was a major inconvenience, as the printer was on a different floor from most of the users. This experience convinced Stallman of people's need to be free to modify the software they use.^[19]

Richard Greenblatt, a fellow AI Lab hacker, founded Lisp Machines, Inc. (LMI) to market Lisp machines, which he and Tom Knight designed at the lab. Greenblatt rejected outside investment, believing that the proceeds from the construction and sale of a few machines could be profitably reinvested in the growth of the company. In contrast, the other hackers felt that the venture capital-funded approach was better. As no agreement could be reached, hackers from the latter camp founded Symbolics, with the aid of Russ Noftsker, an AI Lab administrator. Symbolics recruited most of the remaining hackers including notable hacker Bill Gosper, who then left the AI Lab. Symbolics forced Greenblatt to also resign by citing MIT policies. While both companies delivered proprietary software, Stallman believed that LMI, unlike Symbolics, had tried to avoid hurting the lab's community. For two years, from 1982 to the end of 1983, Stallman worked by himself to clone the output of the Symbolics programmers, with the aim of preventing them from gaining a monopoly on the lab's computers.^[20]

Stallman argues that software users should have the freedom to share with their neighbor and to be able to study and make changes to the software that they use. He maintains that attempts by proprietary software vendors to prohibit these acts are antisocial and unethical.^[21] The phrase "software wants to be free" is often incorrectly attributed to him, and Stallman argues that this is a misstatement of his philosophy.^[22] He argues that freedom is vital for the sake of users and society as a moral value, and not merely for pragmatic reasons such as possibly developing technically superior software.

In February 1984, Stallman quit his job at MIT to work full-time on the GNU project, which he had announced in September 1983.

GNU project[link]

Richard Stallman in 2003 at the opening ceremony of NIXAL (a GLUG) at Netaji Subhash Engineering College, Calcutta, India

Stallman announced the plan for the GNU operating system in September 1983 on several ARPANET mailing lists and USENET.^[23]

In 1985, Stallman published the GNU Manifesto, which outlined his motivation for creating a free operating system called GNU, which would be compatible with Unix. The name GNU is a recursive acronym for "GNU's Not Unix." Soon after, he started a non-profit corporation called the Free Software Foundation to employ free software programmers and provide a legal infrastructure for the free software movement. Stallman is the nonsalaried president of the FSF, which is a 501(c)(3) non-profit organization founded in Massachusetts.^[24] Stallman popularized the concept of copyleft, a legal mechanism to protect the modification and redistribution rights for free software. It was first implemented in the GNU Emacs General Public License, and in 1989 the first program-independent GNU General Public License (GPL) was released. By then, much of the GNU system had been completed. Stallman was responsible for contributing many necessary tools, including a text editor (Emacs), compiler (GCC), debugger (gdb), and a build automator (gmake). The notable exception was a kernel. In 1990, members of the GNU project began a kernel called GNU Hurd, which has yet to achieve the maturity level required for widespread usage.

In 1991, Linus Torvalds, a Finnish student, used the GNU development tools to produce the Linux kernel. The existing programs from the GNU project were readily ported to run on the resultant platform; most sources use the name Linux to refer to the general-purpose operating system thus formed. This has been a longstanding naming controversy in the free software community. Stallman argues that not using GNU in the name of the operating system unfairly disparages the value of the GNU project and harms the sustainability of the free software movement by breaking the link between the software and the free software philosophy of the GNU project.

Cover picture for O'Reilly Media's book Free as in Freedom

Stallman's influences on hacker culture include the name POSIX^[25] and the Emacs editor. On UNIX systems, GNU Emacs's popularity rivaled that of another editor vi, spawning an editor war. Stallman's take on this was to canonize himself as St. IGNUcius of the Church of Emacs^[26][27] and acknowledge that "vi vi vi is the editor of the beast," while "using a free version of vi is not a sin; it is a penance".^[28]

Around 1992, developers at Lucid Inc. doing their own work on Emacs clashed with Stallman and ultimately forked the software into what would become XEmacs.^[29] Technology journalist Andrew Leonard has characterized what he sees as Stallman's uncompromising stubbornness as common among elite computer programmers:

There's something comforting about Stallman's intransigence. Win or lose, Stallman will never give up. He'll be the stubbornest mule on the farm until the day he dies. Call it fixity of purpose, or just plain cussedness, his single-minded commitment and brutal honesty are refreshing in a world of spin-meisters and multimillion-dollar marketing campaigns.

—Andrew Leonard, Salon.com^[30]

Activism[link]

Richard Stallman giving a speech on "Free Software and your freedom" at the biennale du design of Saint Etienne (2008)

Stallman has written many essays on software freedom and since the early 1990s has been an outspoken political campaigner for the free software movement. The speeches he has regularly given are titled The GNU project and the Free Software movement,^[31] The Dangers of Software Patents,^[32] and Copyright and Community in the age of computer networks.^[33] In 2006 and 2007, during the eighteen month public consultation for the drafting of version 3 of the GNU General Public License, he added a fourth topic explaining the proposed changes.^[34]

Linus Torvalds has criticized Stallman for what he considers "black-and-white thinking" and bringing more harm than good to the free software community.^[35]

Stallman's staunch advocacy for free software inspired the Virtual Richard M. Stallman (vrms), software that analyzes the packages currently installed on a Debian GNU/Linux system, and report those that are from the non-free tree.^[36] Stallman would disagree with parts of Debian's definition of free software.^[37]

In 1999, Stallman called for development of a free on-line encyclopedia through the means of inviting the public to contribute articles.^[38] The resulting GNUPedia was eventually retired in favour of the emerging Wikipedia, which had similar aims and was enjoying greater success.^[39]

In Venezuela, Stallman has delivered public speeches and promoted the adoption of free software in the state's oil company (PDVSA), in municipal government, and in the nation's military. In meetings with Chávez and in public speeches, Stallman criticised some policies on television broadcasting, free speech rights, and privacy.^[40][41] Stallman was on the Advisory Council of Latin American television station teleSUR from its launch^[42] but resigned in February 2011, criticizing pro-Gaddafi propaganda during the 2011 North Africa uprisings.^[43]

In August 2006 at his meetings with the government of the Indian State of Kerala, he persuaded officials to discard proprietary software, such as Microsoft's, at state-run schools. This has resulted in a landmark decision to switch all school computers in 12,500 high schools from Windows to a free software operating system.^[44]

After personal meetings, Stallman has obtained positive statements about the free software movement from the then-President of India, Dr. A.P.J. Abdul Kalam,^[45] French 2007 presidential candidate Ségolène Royal,^[46] and the president of Ecuador Rafael Correa.^[47]

Richard Stallman giving a speech at WSIS-2005

Stallman has participated in protests about software patents,^[48] DRM,^[49][50] and proprietary software.

Protesting against proprietary software in April 2006, Stallman held a "Don't buy from ATI, enemy of your freedom" placard at a speech by an ATI representative in the building where Stallman works, resulting in the police being called.^[51] ATI has since merged with AMD Corporation and has taken steps to make their hardware documentation available for use by the free software community.^[52]

Stallman has also helped and supported the International Music Score Library Project in getting back online, after it had been taken down on October 19, 2007 following a cease and desist letter from Universal Edition.^[53]

After the death of Steve Jobs, Stallman wrote the following eulogy:

Steve Jobs, the pioneer of the computer as a jail made cool, designed to sever fools from their freedom, has died.

As Chicago Mayor Harold Washington said of the corrupt former Mayor Daley, "I'm not glad he's dead, but I'm glad he's gone." Nobody deserves to have to die — not Jobs, not Mr. Bill, not even people guilty of bigger evils than theirs. But we all deserve the end of Jobs' malign influence on people's computing.

Richard Stallman using his Lemote machine at Indian Institute of Technology Madras, Chennai before his lecture on 'Free Software, Freedom and Education' organized by Free Software Foundation, Tamil Nadu (FSFTN).

Unfortunately, that influence continues despite his absence. We can only hope his successors, as they attempt to carry on his legacy, will be less effective.

—Richard Stallman^[54]

Stallman's remark stirred up accusations of being in bad taste, while Eric S. Raymond, author of Cathedral and the Bazaar, summarized that Stallman's statement was not personal, but was simply criticizing walled gardens.^[55]

Stallman's only computer is a Lemote Yeeloong netbook (using the same company's Loongson processor) which he chose because it can run with 100% free software even at the BIOS level, stating "freedom is my priority. I've campaigned for freedom since 1983, and I am not going to surrender that freedom for the sake of a more convenient computer."^[56] Lemote is a joint venture of the Institute of Computing Technology of the Chinese Academy of Sciences, an institution of the State Council of China.

Stallman has suggested that the United States government may encourage^[57][58] the use of software as a service because this would allow them to access users' data without needing a search warrant.^[59][60][61]

Terminology[link]

Richard Stallman gets into his St. iGNUcius avatar at Techniche, IIT Guwahati, India

Stallman places great importance on the words and labels people use to talk about the world, including the relationship between software and freedom. He untiringly asks people to say free software and GNU/Linux, and to avoid the terms intellectual property and piracy (in relation to copyright). His requests that people use certain terms, and his ongoing efforts to convince people of the importance of terminology are a source of regular misunderstanding and friction with parts of the free software and open source communities.

One of his criteria for giving an interview to a journalist is that the journalist agree to use his terminology throughout the article.^[62] Sometimes he has even required journalists to read parts of the GNU philosophy before an interview, for "efficiency's sake".^{[citation needed]} He has been known to turn down speaking requests over some terminology issues.^[63]

Stallman rejects a common alternative term, open source software, because it does not call to mind what Stallman sees as the value of the software: freedom.^[64] Thus it will not inform people of the freedom issues, and will not lead to people valuing and defending their freedom.^[65] Two alternatives which Stallman does accept are software libre and unfettered software, but free software is the term he asks people to use in English. For similar reasons, he argues for the term "proprietary software" rather than "closed source software", when referring to software that is not free software.

Stallman repeatedly asks that the term GNU/Linux, which he pronounces "GNU slash Linux", be used to refer to the operating system created by combining the GNU system and the Linux kernel. Stallman refers to this operating system as "a variant of GNU, and the GNU Project is its principal developer."^[63] He claims that the connection between the GNU project's philosophy and its software is broken when people refer to the combination as merely Linux.^[66] Starting around 2003, he began also using the term GNU+Linux, which he pronounces "GNU plus Linux", to prevent others from pronouncing the phrase "GNU/Linux" as "GNU Linux", which would erroneously imply that the Linux kernel is maintained by the GNU project. (See: GNU/Linux naming controversy)

Stallman argues that the term intellectual property is designed to confuse people, and is used to prevent intelligent discussion on the specifics of copyright, patent, trademark and other laws by lumping together areas of law that are more dissimilar than similar.^[67] He also argues that by referring to these laws as property laws, the term biases the discussion when thinking about how to treat these issues.

These laws originated separately, evolved differently, cover different activities, have different rules, and raise different public policy issues. Copyright law was designed to promote authorship and art, and covers the details of a work of authorship or art. Patent law was intended to encourage publication of ideas, at the price of finite monopolies over these ideas — a price that may be worth paying in some fields and not in others. Trademark law was not intended to promote any business activity, but simply to enable buyers to know what they are buying.^[68]

An example of cautioning others to avoid other terminology while also offering suggestions for possible alternatives, is this sentence of an email by Stallman to a public mailing list:

I think it is ok for authors (please let's not call them creators, they are not gods) to ask for money for copies of their works (please let's not devalue these works by calling them content) in order to gain income (the term compensation falsely implies it is a matter of making up for some kind of damages).^[69]

Personal life[link]

Stallman has devoted the bulk of his life’s energies to political and software activism.^[70] Professing to care little for material wealth, he explains that "I've always lived cheaply ... like a student, basically. And I like that, because it means that money is not telling me what to do."^[71]