69-540: CNET Video is a San Francisco and New York based network showing original programming catering to the niche market of technology enthusiasts, operated by Red Ventures through their CNET brand. CNET Video originated as the television program production arm of CNET Networks in the United States, producing programs starting in the mid-to-late 1990s. It was CNET Networks' first project. Technology-themed television shows produced by CNET Video also aired on G4 in . CNET Video
138-426: A garbage matte to expose only the window areas. In order to have figures in one exposure actually move in front of a substituted background in the other, a travelling matte was needed, to occlude the correct portion of the background in each frame. In 1918 Frank Williams patented a travelling matte technique, again based on using a black background. This was used in many films, such as The Invisible Man . In
207-474: A stage hypnotist . In 1882 he teamed up with Douglas Blackburn in an act at the Brighton Aquarium involving muscle reading , in which the blindfolded performer identifies objects selected by the audience, and second sight , in which the blindfolded performer finds objects hidden by his assistant somewhere in the theatre. The Society for Psychical Research (SPR) accepted Smith's claims that
276-598: A "key". Green is used as a backdrop for TV and electronic cinematography more than any other colour because television weather presenters tended to wear blue suits. When chroma keying first came into use in television production, the blue screen that was then the norm in the movie industry was used out of habit, until other practical considerations caused the television industry to move from blue to green screens. Broadcast-quality colour television cameras use separate red, green and blue image sensors, and early analog TV chroma keyers required RGB component video to work reliably. From
345-427: A bright and saturated image. There are several different quality- and speed-optimised techniques for implementing colour keying in software. 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 fully in the green screen, α ≥ 1 means
414-484: A chroma-key background and inserted into the background shot with a distortion effect, in order to create a cloak that is marginally detectable. Difficulties emerge with blue screen 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
483-463: A computer can use these markers to compute the camera's position and thus render an image that matches the perspective and movement of the foreground perfectly. Modern advances in software and computational power have eliminated the need to accurately place the markers — the software figures out their position in space; a potential disadvantage of this is that it requires camera movement, possibly contributing to modern cinematographic techniques whereby
552-416: A default value of 1.0. A very simple g () is ( r , min( g , b ), b ). This is fairly close to the capabilities of analog and film-based screen pulling. Modern examples of these functions are best described by two closed nested surfaces in 3D RGB space, often quite complex. Colours inside the inner surface are considered green screen. Colours outside the outer surface are opaque foreground. Colours between
621-446: A field monitor, to the side of the screen, to see where they are putting their hands against the background images. A newer technique is to project a faint image onto the screen. 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 be composited together, which allows actors to be filmed separately and then placed together in
690-425: A filter or the high contrast film's colour sensitivity to expose only blue (and higher) frequencies. Blue light only shines through the colour negative where there is not blue in the scene, so this left the film clear where the blue screen was, and opaque elsewhere, except it also produced clear for any white objects (since they also contained blue). Removing these spots could be done by a suitable double-exposure with
759-460: A green screen and the Green Goblin had to be shot in front of a blue screen. The colour difference is because Spider-Man wears a costume which is red and blue in colour and the Green Goblin wears a costume which is entirely green in colour. If both were shot in front of the same screen, parts of one character would be erased from the shot. For a clean division of foreground from background, it
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#1732765062006828-515: A green top to make it appear that the subject has no body), because the clothing may be replaced with the background image/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
897-668: A joint show of Smith and Méliès' films at the Alhambra Theatre , Brighton in late 1898 and early 1899. In 1899 Smith, with the financial assistance of Urban, constructed a glass house film studio at St. Ann's Well Gardens, ushering in a highly creative period for him as a film maker. That year he shot the single scene The Kiss in the Tunnel (1899) which was then seamlessly edited into Cecil Hepworth 's View From an Engine Front - Train Leaving Tunnel (1899) to enliven
966-530: A monkey house, a fortune teller, a hermit living in a cave and magic lantern shows of a series of dissolving views . Smith also began to present these dioramic lectures at the Brighton Aquarium, where he had first performed with Douglas Blackburn in 1882. Smith's skilful manipulation of the lantern, cutting between lenses (from slide to slide) to show changes in time, perspective and location necessary for story telling, would allow him to develop many of
1035-433: A narrow frequency band, which can then be separated from the other light using a prism, and projected onto a separate but synchronized film carrier within the camera. This second film is high-contrast black and white, and is processed to produce the matte. 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
1104-420: A quarter of the time needed for other methods. In principle, any type of still background can be used as a chroma key instead of a solid colour. First the background is captured without actors or other foreground elements; then the scene is recorded. The image of the background is used to cancel the background in the actual footage; for example in a digital image, each pixel will have a different chroma key. This
1173-463: A reasonable match. For outdoor scenes, overcast days create a diffuse, evenly coloured light which can be easier to match in the studio, whereas direct sunlight needs to be matched in both direction and overall colour based on time of day. A studio shot taken in front of a green screen will naturally have ambient light the same colour as the screen, due to its light scattering. This effect is known as spill . This can look unnatural or cause portions of
1242-483: A scene featuring a genie escaping from a bottle was the first use of a proper bluescreen process to create a travelling matte for The Thief of Bagdad (1940), which won the Academy Award for Best Special Effects that year. In 1950, Warner Brothers employee and ex- Kodak researcher Arthur Widmer began working on an ultraviolet travelling matte process. He also began developing bluescreen techniques: one of
1311-440: A technological perspective it was equally possible to use the blue or green channel, but because blue clothing was an ongoing challenge, the green screen came into common use. Newscasters sometimes forget the chroma key dress code, and when the key is applied to clothing of the same colour as the background, the person would seem to disappear into the key. Because green clothing is less common than blue, it soon became apparent that it
1380-435: Is a 2012 Technology People's Voice Webby Award Winner.On July 24, 2013, CNET Video launched a new CNET Video+ app for ,and Xbox SmartGlass. Current programming of CNET Video consists of short-form video shot in-studio or in front of a greenscreen and long-form video productions made of packaged clips or new content. All current productions are distributed as podcasts and most programming is available for download at CNET , on
1449-405: Is achieved by a simple numerical comparison between the video and the pre-selected colour. If the colour 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. In order to create an illusion that characters and objects filmed are present in the intended background scene, the lighting in the two scenes must be
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#17327650620061518-451: Is also important that clothing and hair in the foreground shot have a fairly simple silhouette, as fine details such as frizzy hair may not resolve properly. Similarly, partially transparent elements of the costume cause problems. Blue was originally used for the film industry as making the separations required a film that would only respond to the screen colour, and film that responded only to blue and higher frequencies (ultraviolet, etc.)
1587-496: Is best to have as narrow a colour range as possible being replaced. A shadow would present itself as a darker colour 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 or scenes reshot. 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
1656-409: Is some use of the specific full-intensity magenta colour #FF00FF in digital colour images to encode (1-bit) transparency; this is sometimes referred to as "magic pink". This is not a photographic technique and the extraction of the foreground from the background is trivial. The biggest challenge when setting up a blue screen or green screen is even lighting and the avoidance of shadow because it
1725-437: Is sometimes referred to as a difference matte . However, this makes it easy for objects to be accidentally removed if they happen to be similar to the background, or for the background to remain due to camera noise or if it happens to change slightly from the reference footage. A background with a repeating pattern alleviates many of these issues, and can be less sensitive to wardrobe colour than solid-colour backdrops. There
1794-468: Is still running). Greenscreen Chroma key compositing , or chroma keying , is a visual-effects and post-production technique for compositing (layering) two or more images or video streams together based on colour hues ( chroma range). The technique has been used in many fields to remove a background from the subject of a photo or video – particularly the newscasting , motion picture , and video game industries. A colour range in
1863-573: The Natural Color Kinematograph Company , intended to commercially exploit the Kinemacolor process. Urban’s future wife, Ada Jones, purchased the Kinemacolor patent from Smith. This enabled Urban to sell Kinemacolor licenses all around the world. Smith felt he was cheated into selling his invention too cheaply, and Urban believed that Smith was selling secrets to rival inventors. However, Smith remained an employee of
1932-407: The focal length of the lenses used can affect the success of chroma key. Another challenge for blue screen or green screen is proper camera exposure . Underexposing or overexposing a coloured backdrop can lead to poor saturation levels. In the case of video cameras, underexposed images can contain high amounts of noise , as well. The background must be bright enough to allow the camera to create
2001-690: The iTunes Store and on the CNET Video app for platforms such as Roku . A 24-hour CNET channel can be found on Pluto TV channel 684 (this channel was added to the service well before the two became sister properties by the re-merger of Viacom and CBS in late 2019). Until Summer 2012, CNET Video streamed live programming on its subsite CNET Live , consisting of audio talk shows with video feeds, which also were distributed as podcasts . On March 23, 2012, CNET TV's flagship talk show Buzz Out Loud announced that it and most of CNET Live will be cancelled for more on-demand content (save for The 404 Show, which
2070-437: The 1920s, Walt Disney used a white backdrop to include human actors with cartoon characters and backgrounds in his Alice Comedies . The blue screen method was developed in the 1930s at RKO Radio Pictures . At RKO, Linwood Dunn used an early version of the travelling matte to create "wipes" – where there were transitions like a windshield wiper in films such as Flying Down to Rio (1933). Credited to Larry Butler ,
2139-749: The Natural Color Kinematograph Company and testified on its behalf during the 1914 lawsuit by rival inventor William Friese-Greene , which challenged Smith's Kinemacolor patent. Smith's patent for the Kinemacolor process was revoked in 1915, after which it faded out of public view. In the late 1940s he was rediscovered by the British film community, being made a Fellow of the British Film Academy in 1955. Smith died in Brighton on 17 May 1959. Hove Museum has
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2208-841: The Star Films studio in Montreil, Paris, on a pre-enactment of the Coronation of Edward VII and Alexandra of Denmark commissioned by Charles Urban of the Warwick Trading Company after rival company Mutoscope and Biograph acquired the rights to film the actual event. In 1903 Charles Urban left the Warwick Trading Company to form the Charles Urban Trading Company taking the rights to Smith's films with him, at what marked
2277-614: The act was genuine and after becoming a member of the society he was appointed private secretary to the Honorary Secretary Edmund Gurney from 1883 to 1888. In 1887, Gurney carried out a number of "hypnotic experiments" in Brighton, with Smith as his "hypnotiser", which in their day made Gurney an impressive figure to the British public. Since then it has been heavily studied and critiqued by Trevor H. Hall in his study The Strange Case of Edmund Gurney . Hall concluded that Smith (using his stage abilities) faked
2346-405: The actor in front of a blue screen together with the background footage, one frame at a time. In the early 1970s, American and British television networks began using green backdrops instead of blue for their newscasts. During the 1980s, minicomputers were used to control the optical printer. For the film The Empire Strikes Back , Richard Edlund created a "quad optical printer" that accelerated
2415-566: The background as the subject moves. Prior to the introduction of travelling mattes and optical printing , double exposure was used to introduce elements into a scene which were not present in the initial exposure. This was done using black draping where a green screen would be used today. George Albert Smith first used this approach in 1898. In 1903, The Great Train Robbery by Edwin S. Porter used double exposure to add background scenes to windows which were black when filmed on set, using
2484-453: 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 in the 1990s of practical blue LEDs, which also allow for emerald green LEDs. There is also a form of colour keying that uses light spectrum invisible to human eye. Called Thermo-Key, it uses infrared as
2553-478: The camera being more sensitive to green light. In analog television , colour 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 pre-selected colour. In-phase portions of the video are replaced by the alternate background video. In digital colour TV , colour is represented by three numbers (red, green, blue intensity levels). Chroma key
2622-452: The camera is always in motion. The principal subject is filmed or photographed against a background consisting of a single colour or a relatively narrow range of colours, usually blue or green because these colours are considered to be the furthest away from skin tone. The portions of the video which match the pre-selected colour are replaced by the alternate background video. This process is commonly known as " keying ", "keying out" or simply
2691-454: The characters to disappear, so must be compensated for, or avoided by using a larger screen placed far from the actors. The depth of field used to record the scene in front of the coloured screen should match that of the background. This can mean recording the actors with a larger depth of field than normal. A chroma key subject must avoid wearing clothes which are similar in colour to the chroma key colour(s) (unless intentional e.g., wearing
2760-445: The cleanest key. In the digital television and cinema age, much of the tweaking that was required to make a good quality key has been automated. However, the one constant that remains is some level of colour coordination to keep foreground subjects from being keyed out. Before electronic chroma keying, compositing was done on (chemical) film. The camera colour negative was printed onto high-contrast black and white negative, using either
2829-409: The colour positive (thus turning any area containing red or green opaque), and many other techniques. The result was film that was clear where the blue screen was, and opaque everywhere else. This is called a female matte , similar to an alpha matte in digital keying. Copying this film onto another high-contrast negative produced the opposite male matte . The background negative was then packed with
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2898-571: The end of his most active period as a film-maker. In 1904, A. H. Tee took over the lease on St Ann's Well Gardens, and Smith moved to a new home in Southwick , Sussex , dubbed Laboratory Lodge , where with finance from Charles Urban, he went on to develop the Lee-Turner Process , which had been acquired by Urban following the death of Edward Raymond Turner in 1903, into the first successful colour film process, Kinemacolor . Smith
2967-663: The end of his twice-daily programme of projected entertainment at the Brighton Aquarium, as an outlet for his burgeoning film production. Many of Smith's early films, including The Miller and the Sweep and Old Man Drinking a Glass of Beer (both filmed in 1897) were comedies thanks to the influence of his wife, Laura Bayley , who had previously acted in pantomime and comic revue. However Smith also corresponded with special effects pioneer Georges Méliès whose influence can be seen in The X-Rays and The Haunted Castle (both 1897)
3036-433: The female matte and exposed onto a final strip of film, then the camera negative was packed with the male matte and was double-printed onto this same film. These two images combined creates the final effect. The most important factor for a key is the colour separation of the foreground (the subject) and background (the screen) – a blue screen will be used if the subject is predominantly green (for example plants), despite
3105-514: The first films to use them was the 1958 adaptation of the Ernest Hemingway novella, The Old Man and the Sea , starring Spencer Tracy . The name "Chroma-Key" was RCA 's trade name for the process, as used on its NBC television broadcasts, incorporating patents granted to RCA's Albert N. Goldsmith. A very early broadcast use was NBC's George Gobel Show in fall 1957. Petro Vlahos
3174-476: The first successful colour film process, Kinemacolor . Smith was born in Cripplegate , London in 1864. His father Charles Smith was a ticket-writer and artist. He moved with his family to Brighton, where his mother ran a boarding house on Grand Parade, following the death of his father. It was in Brighton in the early 1880s that Smith first came to public attention touring the city's performance halls as
3243-715: The foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as colour keying , colour-separation overlay ( CSO ; primarily by the BBC ), or by various terms for specific colour-related variants such as green screen or blue screen ; chroma keying can be done with backgrounds of any colour that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from any human skin colour . No part of
3312-427: The green channel. Green can also be used outdoors where the light colour temperature is significantly blue. Red is avoided as it is in human skin, and any other colour is a mix of primaries and thus produces a less clean extraction. A so-called " yellow screen " is accomplished with a white backdrop. Ordinary stage lighting is used in combination with a bright yellow sodium lamp. The sodium light falls almost entirely in
3381-414: The green screen two stops higher than the subject, or vice versa. Sometimes a shadow can be used to create a visual effect. Areas of the blue screen or green screen with a shadow on them can be replaced with a darker version of the desired background video image, making it look like the person is casting a shadow on them. Any spill of the chroma key colour will make the result look unnatural. A difference in
3450-438: The image in which the colour is blue. If the news presenter wears blue clothes, their clothes will also be replaced with the background video. Chroma keying is also common in the entertainment industry for visual effects in movies and video games. Rotoscopy may instead be carried out on subjects that are not in front of a green (or blue) screen. Motion tracking can also be used in conjunction with chroma keying, such as to move
3519-423: The key colour, which would not be replaced by background image during postprocessing . For Star Trek: The Next Generation , an ultraviolet light matting process was proposed by Don Lee of CIS Hollywood 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
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#17327650620063588-411: The later of which, along with The Corsican Brothers , Photographing a Ghost and, perhaps his most accomplished work from this time, Santa Claus (all 1898), include special effects created using a process of double-exposure patented by Smith. Many of Smith's films were acquired for distribution by Charles Urban for the Warwick Trading Company and the two began a long business relationship with
3657-409: 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 colour range. In order to get the cleanest key from shooting green screen, it is necessary to create a value difference between the subject and the green screen. In order to differentiate the subject from the screen, a two-stop difference can be used, either by making
3726-439: The pixel is fully in the foreground object, and intermediate values indicate the pixel is partially covered by the foreground object (or it is transparent). A further function g ( r , g , b ) → ( r , g , b ) is needed to remove green spill on the foreground objects. A very simple f () function for green screen is A ( r + b ) − Bg where A and B are user adjustable constants with
3795-462: The process considerably and saved money. He received a special Academy Award for his innovation. For decades, travelling 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. Meteorologists on television often use
3864-535: The results that Gurney trusted in his research papers, and this may have led to Gurney's mysterious death from a narcotic overdose in June 1888. Following Gurney's death, his successors, F. W. H. Myers and Frank Podmore , continued to employ Smith as their private secretary. In 1889, he co-authored (with Henry Sidgwick and Eleanor Mildred Sidgwick ) the paper, Experiments in Thought Transference , for
3933-441: The same scene. Chroma key allows performers to appear to be in any location without leaving the studio. Advances in computer technology have simplified the incorporation of motion into composited shots, even when using handheld cameras. Reference points such as a painted grid, X's marked with tape, or equally spaced tennis balls attached to the wall, can be placed onto the coloured background to serve as markers. In post-production,
4002-580: The scene, and values from user-drawn masks. These produce closed surfaces in space with more than three dimensions. 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. George Albert Smith (film pioneer) George Albert Smith (4 January 1864 – 17 May 1959)
4071-699: The skills he would later put to use as a pioneering film maker developing the grammar of film editing. Smith had attended the Lumière programme in Leicester Square in March 1896 and spurred on by the films of Robert Paul , which played in Brighton for that summer season, he and local chemist James Williamson acquired a prototype cine cameras from local engineer Alfred Darling , who had begun to manufacture film equipment after carrying out repairs for Brighton-based film pioneer Esmé Collings . In 1897, with
4140-593: The society's journal. Blackburn publicly admitted fraud in 1908 and again in 1911, although Smith consistently denied it. In 1892, after leaving the SPR, he acquired the lease of the St. Ann's Well Gardens in Hove from the estate of financier and philanthropist Sir Isaac Lyon Goldsmid , which he cultivated into a popular pleasure garden, where from 1894 he started staging public exhibitions of hot air ballooning, parachute jumps,
4209-713: The staid phantom ride genre and demonstrate the possibilities of creative editing. The following year he experimented with reversing in The House That Jack Built (1900), developed dream-time and the dissolve effect in Let Me Dream Again (1900) and pioneered the use of the close-up with Grandma's Reading Glass , As Seen Through a Telescope and Spiders on a Web (all 1900). Film historian Frank Gray describes this experimental period, from 1897 to 1900, as Smith's laboratory years. In 1902 Smith collaborated with old friend Georges Méliès at
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#17327650620064278-411: The subject being filmed or photographed may duplicate the colour used as the backing, or the part may be erroneously identified as part of the backing. It is commonly used for live weather forecast broadcasts in which a news presenter is seen standing in front of a large CGI map which is really a large blue or green background. Using a blue screen, different weather maps are added on the parts of
4347-409: The surfaces are partially covered, they are more opaque the closer they are to the outer surface. Sometimes more closed surfaces are used to determine how to remove green spill. It is also very common for f () to depend on more than just the current pixel's colour, it may also use the ( x , y ) position, the values of nearby pixels, the value from reference images or a statistical colour model of
4416-486: The technical assistance of Darling and chemicals purchased from Williamson, Smith turned the pump house into a film factory for developing and printing and developed into a successful commercial film processor as well as patenting a camera and projector system of his own. Both he and his neighbour Williamson would go on to become pioneering film makers in their own right creating numerous historic minute-long films. On 29 March 1897, Smith added animated photographs to
4485-665: Was an English stage hypnotist , psychic , magic lantern lecturer, Fellow of the Royal Astronomical Society , inventor and a key member of the loose association of early film pioneers dubbed the Brighton School by French film historian Georges Sadoul . He is best known for his controversial work with Edmund Gurney at the Society for Psychical Research , his short films from 1897 to 1903, which pioneered film editing and close-ups, and his development of
4554-410: Was awarded an Academy Award for his refinement of these techniques in 1964. His technique exploits the fact that most objects in real-world scenes have a colour whose blue-colour component is similar in intensity to their green-colour component. Zbigniew Rybczyński also contributed to bluescreen technology. An optical printer with two projectors, a film camera and a "beam splitter", was used to combine
4623-427: Was easier to use a green matte screen than it was to constantly police the clothing choices of on-air talent. Also, because the human eye is more sensitive to green wavelengths, which lie in the middle of the visible light spectrum, the green analog video channel typically carried more signal strength, giving a better signal to noise ratio compared to the other component video channels, so green screen keys could produce
4692-507: Was far easier to manufacture and make reliable than film that somehow excluded both frequencies higher and lower than the screen colour. In television and digital film making, however, it is equally easy to extract any colour, and green quickly became the favoured colour. Bright green is less likely to be in the foreground objects, colour film emulsions usually had much finer grain in the green, and lossy compression used for analog video signals and digital images and movies retain more detail in
4761-471: Was granted a patent for the new process, which abandoned the three-colour approach of Edward Turner in favour of a two-colour (red-green) The process was first demonstrated on 1 May 1908, followed by further demonstrations in 1908 and public demonstration from early 1909 as far afield as Paris and New York, for which Smith was awarded a silver medal by the Royal Society of Arts . In 1909 Urban founded
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