], literally - “color key”; from Greek χρώμα - “color”) is a technology for combining two or more images or frames in one composition, color electronic key projection (or key projection), used on television and in modern digital film production technology. Using chromakey, you can “remove” the background and “add” an image or video through a video editor. Also in everyday life chromakey they call the screen itself, against which they are filming.
Some sources in Russian use the following names: key projection, key projection, chroma key, color keying, teleinlay, chromakey, chroma key, sometimes in Russian transliteration "chroma key". Another name for the technology is keying(eng. keying, color keying).
Story
Origin
In cinema before the advent of television technology and digital ways Film production used methods of combining the acting scene with the background, known as “rear projection”, “front projection” and “wandering mask”, giving a visual effect similar to chromakey.
Blue screen
Blue screen technology was created in the 1930s by the film studio RKO Pictures.
Technology
The most common colors used in projection are green and blue (cyan), because such colors are not found in human skin tones. The most popular background color for combined filming in film production is green (which gave the technology its name “ Green screen"), for television programs a blue background is more often used (" Blue screen"), although the color of the fabric for “keying” depends on the creative task set by the director and the characteristics of the equipment on which the projection is made, as well as the color of clothing and objects present in the frame.
The use of computers makes it easier to combine several images with each other, even if the shooting is done handheld.
The main subject is photographed against a background of one color or against a background with a relatively small difference in colors. Usually blue or green backgrounds are used, since human skin does not have such colors. The process of replacing the original background with another is called compositing or keying.
Blue chromakey
Blue chromakey was widely used when shooting on film. The color negative was printed on high-contrast black-and-white film using a color filter that eliminated the blue channel. This area became completely black, creating an alpha channel. Then another image was superimposed using double exposure.
Green chromakey
Currently, the green background is used most often, since digital cameras are most sensitive to green shades due to the Bayer filter matrices they use. The image in the green channel contains less noise, is cleaner and is easier to process with high quality during compositing. The green background became more widely used due to the widespread use of blue jeans, as well as the presence of blue eyes in people.
Basic conditions
The main factor is the significant color difference between the foreground (subject being photographed) and the background (green screen). For example, a blue box on a green background.
Lighting
If the subject being photographed is close to the green screen, then re-reflected light may fall on it. In such cases, human skin acquires a green tint or green shades appear in glossy metal and glass surfaces. This effect is called spill:p20. The solution is to use a larger green screen and increase the distance from the subject to the background.
Camera
Cloth
You should avoid clothing that contains shades close to the background colors, because clothing can be removed in a video editor along with the background.
However, sometimes clothes of the same colors are specifically used. This is how the scene in the Harry Potter film with the invisibility cloak was filmed. The foreground distorts the background and creates the desired effect.
In this case, difficulties may arise when there must be two objects in the frame at once, one of which is blue and the other green. So in the movie Spider-Man there is a fight scene between the main character and the Green Goblin. Each character had to be shot separately against a contrasting background.
To facilitate the compositing process, the boundaries between the main subject and the background should be clearly separated. The greatest difficulties are caused by translucent objects, such as individual locks of hair, transparent raincoats or umbrellas, glass.
Background color
The blue background was most often used when shooting on film.
The green background is more often used outdoors, in shots where the sky is visible. Digital cameras They perceive green tones better and record them with less noise.
A red background is used for scenes where objects are being photographed rather than people, since red skin tones do not allow such a background to be used.
When shooting on film, a yellow screen is also used:16.
One of the most modern techniques is the use of reflectors. The background is illuminated by LED lamps located as close as possible to the camera lens, the light from which is returned to the lens. This technology allows the use of lamps with minimal power and much smaller sizes compared to standard solutions.
Thermo-Key technology uses light in the infrared spectrum, invisible to the human eye.
It is also possible to use ultraviolet light. These special fluorescent lamps were used during the filming of Star Trek: The Next Generation.
In addition, instead of a single-color background, any colored static image can be used for keying. To do this, first the background used as chromakey is shot from a tripod without any actors or objects in the foreground. Then, without moving the camera, the main subject is shot against the same background. And then in the video editor, using the subtraction method, only the main object is left. However, it is extremely important that the objects in the background do not move. And also so that there is no noise in the image. A textured background is more often used when the main subject has many different colors.
Additional requirements
Light uniformity
To make it easier to separate the subject from the background, it is necessary to avoid shadows and highlights in chromakey and illuminate it as evenly as possible. The matte surface of the background reflects light more evenly and there are no bright reflections on it.
In this case, sometimes they deliberately leave a shadow from the object being photographed on the background in order to use it when combining layers.
Exposition
To obtain a high-quality result, it is important to set the exposure correctly in the camera. A background that is too dark or too light will have insufficient color saturation. If the image is too dark, it will contain noise, which will also negatively affect the quality of the material.
Criticism
Advantages
Thanks to the use of chromakey, you can significantly reduce the cost of the production process. And also create or combine objects that cannot exist in reality.
Flaws
The disadvantage of chromakey is that if a person’s clothing has a color similar to the background color, then the person begins to “shine through” (“glow”). Therefore, when choosing a costume for an actor or TV presenter, avoid colors that match the background. Although this problem can be solved by applying masks in a video editor.
Compositing programs
see also
Notes
- Felix Voroisky. Computer science. Encyclopedic dictionary-reference book. - Litres, 2016-01-28. - P. 413. - 769 p. - ISBN 9785457966338.
- Make a movie. DIY chromakey (undefined) . snimikino.com articles. Retrieved January 10, 2017.
- Dictionary Lingvo Electronics (En-Ru) chromakey - color electronic key projection
- Sergey Orlov. English - Russian dictionary of computer technology and information technology. - P. 139.
- Mastering 3ds max 5. - Williams Publishing House, 2004. - P. 37. - 771 p. - ISBN 9785845905499.
- Team of authors. Adobe Premiere Pro CC. - Litres, 2014. - P. 444. - 543 p. - ISBN 9785457592391.
- Television and radio broadcasting. - 1990. - P. 190. - 776 p.
- Eduard Efimov. Television yesterday, today, tomorrow. - Art, 1983. - P. 141. - 248 p.
- Directory of licenses of the Federal Service for Television and Radio Broadcasting of the Russian Federation and the Ministry of Communications of the Russian Federation. . - 625, 1995. - P. 193. - 200 p.
- Kiryanova E. Video editing, animation and DVD authoring for everyone: Adobe Premiere Pro CS4 and After Effects CS4. - BHV-Petersburg, 2010. - P. 184. - 416 p. - ISBN 9785977503839.
- Kathryn Ramey. Experimental Filmmaking: Break the Machine. - P. 70.
- Foster, Jeff. The Green Screen Handbook: Real-World Production Techniques. - John Wiley & Sons, 2010. -
On a green background. The heroes do something, run, jump, and then we see how they do it in space or in some other fantastic environment. The process of replacing the background is called keying, and the technique of combining two or more pictures is called chromakey (from English chroma key - “color key”). I'll tell you how to do it DIY chromakey.
As you already understood, we will need a background, light and a background replacement program.
The background for chromakey is called greenscreen (from English green screen - green screen) or bluescreen (from English blue screen - blue screen), depending on the color. A suitable background can be purchased for as little as $200 (the price is affected by the size of the background, the presence of stands and the quality of the fabric). But since the article is called “CHROMAKEY WITH YOUR OWN HANDS,” I will tell you how I made the background for the chromakey.
Like everyone else, I knew that the fabric should be green, or rather light green. But after searching all the fabric stores in the city, I realized that I couldn’t find the right shade. Therefore, in order not to waste money, I bought blue fabric, which is also great for chromakey.
WHY ONLY BLUE AND GREEN?
As you may have guessed, in the last stage of keying we will select the background color with an eyedropper and “remove” this color from the image. If the background color is, for example, red, then the faces of the actors will disappear along with the background. And blue and green, as it turned out, are the most opposite colors to skin color.
As someone who shot chromakey on a blue screen for several years, I can say the following:
- You can’t shoot blue things against a blue background - this was a problem for me when I realized that half of my things were blue;
- if your actor is black, it's best to use green screen.
WHAT TO MAKE A SCREEN FROM
My first screen was made of paper. I didn’t have money for fabric, much less for a professional screen. So I decided to buy light green A4 paper and glue it with tape. I couldn't find lime green paper, so I bought white paper and lime green markers. Oh yes, I was a persistent guy! Over the course of a few days, I colored the paper with markers in a light green color. with total area 3 m2. And he attached this work to a wooden frame. In general, the background turned out well, but the tape that I used to fasten the sheets together cast glare that remained as white dots in the video. For some time I deleted them manually, and then abandoned this matter and made another background.
The second background was blue, and it would be made of fabric. I bought 6 meters of blue fabric, which I cut in half and sewed together. As a result, I got a blue canvas 3mx2.8m. I hung this screen in my room on top of the curtains - this is how the problem with the stands was solved.
The first thing you realize when working with chromakey is that you need a lot of light. You should have a separate set of lights for the screen so that there are no shadows on it. You should also position your subject away from the screen so that their shadow does not fall on the screen. You should ensure that the screen in the video looks as monochromatic as possible. Make sure there are no overexposed or dark areas. This will help make better keying.
When it comes to lighting your subject, think about the end result. Where will you move your hero? What light sources will shine on it in the virtual environment? In accordance with this and c, you need to light your hero so that when replacing the background, random highlights or shadows do not raise questions. Also, if possible and consistent with the intended environment, illuminate the subject with backlight (the light is located opposite the camera and illuminates the “invisible” side of the object) - this way you will make the picture more voluminous and better separate your hero from the background.
III. SHOOTING.
Watch the edges of the frame!
First, your green (or blue) screen needs to extend to the edges of the frame so that you can crop your subject even if they end up on the edge of the frame.
Second, if you're filming a person, make sure they don't wave their arms too much. If the frame boundaries cut off his arms, you won't be able to move him around the frame when you replace the background.
IV. REPLACING THE BACKGROUND.
I'm doing a background replacement in Adobe After Effect. There is a very good effect called Keylight. Using this effect, you can make very high-quality cuttings. I learned this from Andrew Kramer, who you can always find at videocopilot.net. On the Internet there is a video tutorial of his, translated into Russian, dedicated to chromakey in After Effect. I suggest you watch it (the lesson starts at 2:30).
Perhaps this is all on the topic “Do-it-yourself Chromakey”. Now there is nothing stopping you from building your own film studio in your home or garage. Post links to what you came up with in the comments. Here's what I once did:
Chromakey(English chroma key - literal translation "color key") is a technology for combining two or more images or chroma key, which is used in cinema and television.
Actress Marcy Williams in front of the blue wall, which will later turn into a beautiful harbor in the TV series Game of Thrones
During filming, the object is placed on a single-color background, which allows you to place another image in place of the background during editing. Also in the bypass, chromakey refers to the color key screen itself, against which the shooting is performed. Another common name for the technology is keying (color keying).
Scene from the movie "Deadly Honeymoon" before and after special effects
The most common colors used in key projection are green and blue (cyan). This is due to the fact that these colors do not contain human skin tones. However, in practice, you can use any other colors, in particular black or white.
Most often, a green screen is used for combined filming in films (which gives the technology the name “Green screen”). On television, blue color (“Blue screen”) is more often used. Although in each individual case the color of the rear screen may depend on the artistic task at hand and the characteristics of the equipment used.
Scene from the series "The Walking Dead"
Chroma key technology allows you to save a lot of money and time when shooting films or TV shows. The only downside is that if the person being photographed’s clothes contains a color similar to the background color, the person begins to “shine through” (“glow”). In this connection, when choosing a costume for actors or TV presenters, avoid colors that match the background.
A few examples of “before and after” - the shooting of famous films and the result after processing and editing.
How to use chromakey in action
"The Secret is in His Eyes"
Film "Ugly" - interview
Filming of the film "Paranoia" - street cafe
Abandoned military camp near the hospital from The Walking Dead
Of course, the use of chromakey is far, far from being limited to these scenes! Below are a few more pairs of photographs from the filming of famous films and TV series of recent times.
"Life of Pi" and special effects with a boat and a tiger
Chroma key is a technology that allows you to change the background of a video or photographic material. To do this, the original footage is processed by a special computer program.
Why do you need chromakey technology?
Where can I use chromakey? It is actively used by video makers, video bloggers, in advertising and the film industry.
Using chromakey allows you to simplify the process of obtaining finished processed video material. Agree, it is much cheaper, faster and easier to complete the missing surroundings and elements on the computer than to rebuild a studio and fill it with full-scale decorations.
Chroma key successfully copes with this task: you can easily shoot video in any room, including your home, and only then process the material with software. And now - in front of you is a video, made as if at the sea, in the mountains or in a television studio.
Types of chromakey
You can process a video that has any background, but mainly green and blue colors are used for chromakey. Why? These two shades are not typical for natural human skin, which facilitates software processing of video material.
Typically, fabric is used for chromakey, and it must meet the following conditions: be plain, matte, i.e., eliminate glare.
Sometimes for this technology they take special chromakey paper or paint the walls in the required color.
Instructions for creating chromakey at home
- Measure the area of the wall or other surface near which the shooting will take place.
- In the sewing department, buy a piece of fabric of the required size. When choosing fabric, rely on the following requirements:
- The color of the canvas should be blue or green.
- Buy the material in one color.
- The surface of the fabric can only be matte, not shiny, and not giving glare when light hits it.
- Fasten the selected canvas to a wall or other surface using buttons. You can build a frame base and fix the fabric on it. The fabric should be stretched evenly, without folds or folds.
- Prepare lighting. In addition to the subject, the background fabric will also be illuminated. You need to try to ensure that the lighting of the entire surface is uniform, with a single color shade. This is the only way to use keying to exclude this color from the editor and insert the necessary elements.
That is why there will be 4 light sources: two of them are placed on both sides of the object being photographed; the third, frontal, is directed towards the object; and the last one is installed on the side or behind the person being removed.
- Proceed directly to shooting. The subject should be placed 50 cm from the background fabric. This will separate the background during keying.
When placing an object, you need to monitor the location of the light and prevent shadows from falling on the chromakey.
Important: there should not be any elements on the subject that match the color of the background screen. It is even more reliable if there are no similar shades.
- The footage is processed with a special program. You can find a sufficient number of paid and free versions on the Internet. The most common options are: Sony Vegas Pro and Adobe After Effects.
A few words about Sony Vegas Pro. This is a simple program, easy to use and understandable even for beginners, while its functionality is quite impressive.
And lastly, it is preferable to make video with a camera whose resolution is at least HD or Full HD, since the quality of keying depends on the source material.
Video
Today we dive into the history of visual deception in Hollywood. She is also a backstory modern composition the so-called green screen (Green Screen) or chromakey (Chromakey).
Magic screen
Now that video cameras and computers are everywhere in modern world, it's easy to forget that the first motion pictures were themselves special effects. Here, at the beginning of the film industry, we will begin our journey. The end of the 19th century, one of the first world cinematographers, creating several films a year, a man who studied the art of illusion all his life - Georges Méliès.
Georges Méliès
In his film A Man Has Several Heads (1898), Méliès uses a visual trick that is the germ of what we now call green screen composition. Using "matte" for different exposures.
Composition is a way of combining different frames and elements into one image. The matte shot was the first composition technique used by early filmmakers, including Méliès.
In his film, Méliès darkened some parts of the frame with glass and black paint. This "matte" prevented light from reaching the film, preventing it from being exposed. Méliès would then rewind the film and darken everything else, revealing only the part of the film that was underneath the matte finish. The resulting double exposure combined several frames in one. And this was all done inside the camera.
Train
This matte technique was also used in Edwin Porter's 1903 film The Great Train Robbery, but not as a magic trick, but as a way to create a larger, more realistic world.
Note the moving train outside the station window, as well as the open postal car door with the landscape in the background. Both of these shots were done using matte and double exposure.
A natural question arises: “Why didn’t they just film in a real station or train carriage?”
The fact is that at that time it was technically impossible. The first orthochromatic films required a lot of light. And the technology of electric lighting necessary for film will only be invented in a couple of decades. Not to mention the obvious exposure issues that come with shooting indoors and having a window in the frame. Even now, the camera may have problems with brightness differences between indoors and outdoors. In order for the film to look and feel natural, we had to use visual trickery.
During the 1900s and 1920s, the film industry evolved and new ways were developed to expand film sets and create artificial realities.
“Glass shot” is a technique of drawing elements on glass that was placed between the subject and the camera. It's a kind of "natural" composition, perfected by early cinematographer Norman Down. He used it on film sets, visually enlarging and changing them without the expense of construction.
ONE OF THE FIRST CINEMATOGRAPHERS NORMAN DOWN
The disadvantage of using a "glass frame" was that the images had to be ready to shoot. Norman Down solved this problem by painting the glass black and using this frame as a "matte". He then inserted the film into the second camera. After which, the matte artists could paint the background images without haste. This method of drawing "matte" was also used in the golden era of Hollywood. In general, it is still used today, even in the modern digital world.
JAMES CAMERON WORKING ON THE GLASS FRAME FOR ESCAPE TO NEW YORK (1981)
"Black screen
The disadvantage of "matte" is that the camera must be completely still. Nothing should cross the invisible matte line between the actual action and the background image. This is how the moving “matte” appeared.
In 1918, Frank Williams patented and demonstrated in the film Sunrise by Friedrich Wilhelm Murnau (1927) the process of using black "matte". In it, objects were shot against a completely black background. The film was then copied onto very high contrast negatives until it was developed black and white silhouette. This black and white silhouette was used as “matte”. It was called a moving "matte" because it moved along the frame.
This "black-and-white matte" effect was called the Williams Process and it made famous John Fulton's film The Invisible Man (1933). To capture the footage of the Invisible Man undressing, actor Cloud Raines was dressed in a black velvet suit and filmed against a black background. .
The effect produced was so striking and memorable that this method was used in subsequent sequels to the film, even though more efficient processes became available over time.
Blue screen
The Williams Process had its drawbacks. For example, against a changing background, any shadows on the object were not taken into account. An alternative was invented by Dodge Dunning around 1925. It would later be called the Dunning Process.
Colored lighting was used in this process. The screen in the background was illuminated in blue, and the object in the foreground was illuminated in yellow. Using dyes and filters, blue and yellow could be separated from each other to create moving "matte". The Dunning Process was first used in King Kong in 1933.
The disadvantage of the Dunning Process was that it only worked on black and white film. Color film required a different technique. It was created by special effects artist Larry Butler. He demonstrated it in the film “The Thief of Baghdad” (1940). Butler shot the subject against a blue background on a Technicolor three-film camera. Blue was chosen because it is the least represented color in human skin. And blue film has the smallest “grain”.
By separating the blue film from three Technicolor negatives, Butler created a "matte" silhouette similar to Williams' Process. Then, using an optical printer, a relatively new invention at the time that combined different filmstrips into one, Butler first removed the blue background from the front plate, and, using a negative of the changing matte, removed the foreground space from the back plate. The last step was to connect the front and back plates.
This blue screen technique earned Lawrence Butler an Academy Award for Best Special Effects in 1940, but it also had its drawbacks.
Firstly, this process was time consuming, as it involved several steps with an optical printer. Secondly, a significant drawback was the presence of a blue border, almost always visible in the frame.
In addition, it did not take into account small details such as hair, smoke or motion blur.
But despite this, the Blue Screen process was actively used in such box-office films as “The Ten Commandments” in 1956.
"Yellow" chromakey
Hollywood continued to experiment with variations of the blue screen process, including ultraviolet matte, such as in The Old Man and the Sea.
But the real challenger to blue screen was created in the late 50s. And this was done by one of the giants in the world of composition - Petro Vlahos.
PETRO VLACHOS
In the mid-50s, Vlachos developed the "sodium process". This process was used extensively by Walt Disney Studios in the 60s and 70s. The process involved the actors standing in front of a white screen and being standardly lit. The screen itself was illuminated by powerful sodium lamps, similar to orange street lamps.
Sodium vapor produces light of an unusual wavelength - approximately 589.3 nanometers, and no longer. Using a specially coated prism inside an old Technicolor three-film camera, this wavelength of sodium light was separated. Then it was recorded on a special black and white film, automatically creating a moving black and white “matte”. The rest of the light was captured by standard Technicolor film, which is insensitive to yellow-orange sodium light.
This technique created the best moving “matte” of that time. It was first used by Disney in The Parent Trap and then in The Absent-Minded Professor in 1961. In 1964, the sodium process earned the film Mary Poppins an Academy Award for Best Special Effects.
This technique had only one drawback. There was only one sodium prism, so only one chamber in the world could perform this process. This camera belonged to Disney and they did not rent it for small amounts.
Revenge of the Blue Screen
In the late 50s, MGM was going to shoot Ben Hur in the MGM Camera 65 format (65 mm film). Then they turned to Petro Vlahos to help them with the composition. Vlahos
was the inventor of the sodium process.
They didn't want the problems that came with filming The Ten Commandments on a blue screen. But the sodium process could not be used since its prism was made for 35 mm. film, not 65mm.
So Vlahos was asked to do something to improve the blue screen process. After 6 months of difficult work, Vlahos made a discovery.
And here's where things get a little complicated...
Most colors that are not pure green or pure blue contain approximately equal amounts of blue and green.
Therefore, when creating the "matte" of the blue screen, Vlachos separated the green (or positive). He ran it under blue light along with the original color negative, exposing both pieces of film at the same time to create a "blue matte of difference." In this “matte” the blue and green colors matched.
Then, the blue positive was combined with the original negative and placed under red light. This made it possible to obtain a “front” “matte”. This "matte" was superimposed on the original separated colors. The exception was that the blue part was replaced by green with a green difference mask. Although, in essence, this was an artificial blue department.
This difficult process required 12 pieces of film to go from a general negative to a general internegative. But it was amazing because it solved the problems with edges and fine details that blue screen caused.
This process was so successful that it was actively used for almost 40 years. The creation of a microprocessor-based optical printer made it faster and more accurate. This printer was used by Richard Edlund in the movie The Empire Strikes Back. Next big change will be digital.
OPTICAL PRINTER IN “INDUSTRIAL LIGHT & MAGIC” FOR “THE EMPIRE STRIKES BACK”
Digital Green Screen Victory
I deliberately avoided the word " Chromakey" (Further " chromakey") all this time. The fact is that historically this term was applied only to video systems. Now it can be used without fear. In early video mixers, "keyer" was the name given to the mathematical process. It created a color range in the video signal and made it transparent. This is a very common effect that has been used to create special effects. For example, weather maps or almost all TV channel news studios.
Blue screen color still dominated, but green began to take over when digital film post-processing began in the late 90s.
Why green? Mainly because green screen is easier and cheaper to light than blue screen. Green appears brighter on electronic displays, it was good for picking up keys when filming outdoors (where blue could match the color of the sky) and bright green was much less common in actors' clothing than blue.
BAYER FILTER IS A MATRIX OF RED, GREEN AND BLUE PHOTO AREAS ON MANY MODERN DIGITAL CAMERAS.
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