Digital compositing

Four images assembled into one final image

Digital compositing is the process of digitally assembling multiple images to make a final image, typically for print, motion pictures or screen display. It is the digital analogue of optical film compositing. It's part of VFX processing.

Mathematics

The basic operation used in digital compositing is known as alpha blending, where an opacity value, 'α', is used to control the proportions of two input pixel values that end up a single output pixel.

As a simple example, suppose two images of the same size are available and they are to be composited. The input images are referred to as the foreground image and the background image. Each image consists of the same number of pixels. Compositing is performed by mathematically combining information from the corresponding pixels from the two input images and recording the result in a third image, which is called the composited image.

Consider three pixels;

  • a foreground pixel, f
  • a background pixel, b
  • a composited adetpixel, c

and

  • α, the opacity value of the foreground pixel. (α = 1 for an opaque foreground, α = 0 for a completely transparent foreground). A monochrome raster image where the pixel values are to be interpreted as alpha values is known as a matte.

Then, considering all three colour channels, and assuming that the colour channels are expressed in a γ=1 colour space (that is to say, the measured values are proportional to light intensity), we have:

cr = α fr + (1 − α) br
cg = α fg + (1 − α) bg
cb = α fb + (1 − α) bb

Note that if the operations are performed in a colour space where γ is not equal to 1 then the operation will lead to non-linear effects which can potentially be seen as aliasing artifacts (or "jaggies") along sharp edges in the matte. More generally, nonlinear compositing can have effects such as "halos" around composited objects, because the influence of the alpha channel is non-linear. It is possible for a compositing artist to compensate for the effects of compositing in non-linear space.

Performing alpha blending is an expensive operation if performed on an entire image or 3D scene. If this operation has to be done in real time video games, there is an easy trick to boost performance.

cout = α fin + (1 − α) bin
cout = α fin + bin − α bin
cout = bin + α (fin − bin)

By simply rewriting the mathematical expression, one can save 50% of the multiplications required.

Algebraic properties

When many partially transparent layers need to be composited together, it is worthwhile to consider the algebraic properties of compositing operators used. Specifically, the associativity and commutativity determine when repeated calculation can or cannot be avoided.

Consider the case when we have four layers to blend to produce the final image: F=A*(B*(C*D)) where A, B, C, D are partially transparent image layers and "*" denotes a compositing operator (with the left layer on top of the right layer). If only layer C changes, we should find a way to avoid re-blending all of the layers when computing F. Without any special considerations, four full-image blends would need to occur. For compositing operators that are commutative, such as additive blending, it is safe to re-order the blending operations. In this case, we might compute T=A*(B*D) only once and simply blend T*C to produce F, a single operation. Unfortunately, most operators are not commutative. However, many are associative, suggesting it is safe to re-group operations to F=(A*B)*(C*D), i.e. without changing their order. In this case, we may compute S:=A*B once and save this result. To form F with an associative operator, we need only do two additional compositing operations to integrate the new layer S, by computing F:=S*(C*D). This expression indicates compositing C with all of the layers below it in one step, and then blending all of the layers on top of it with the previous result to produce the final image in the second step.

If all layers of an image change regularly but many layers still need to be composited (such as in distributed rendering), the commutativity of a compositing operator can still be exploited to speed up computation through parallelism even when there is no gain from pre-computation. Again, consider the image F=A*(B*(C*D)). Each compositing operation in this expression depends on the next, leading to serial computation. However, associativity can allow us to rewrite F=(A*B)*(C*D) where there are clearly two operations that do not depend on each other that may be executed in parallel. In general, we can build a tree of pair-wise compositing operations with a height that is logarithmic in the number of layers.

Software

The most historically significant nonlinear compositing system was the Cineon, which operated in a logarithmic color space, which more closely mimics the natural light response of film emulsions (the Cineon System, made by Kodak, is no longer in production). Due to the limitations of processing speed and memory, compositing artists did not usually have the luxury of having the system make intermediate conversions to linear space for the compositing steps. Over time, the limitations have become much less significant, and now most compositing is done in a linear color space, even in cases where the source imagery is in a logarithmic color space.

Compositing often also includes scaling, retouching and colour correction of images.

Node-based and layer-based compositing

There are two radically different digital compositing workflows: node-based compositing and layer-based compositing.

Node-based compositing represents an entire composite as a directed acyclic graph, linking media objects and effects in a procedural map, intuitively laying out the progression from source input to final output, and is in fact the way all compositing applications internally handle composites. This type of compositing interface allows great flexibility, including the ability to modify the parameters of an earlier image processing step "in context" (while viewing the final composite). Node-based compositing packages often handle keyframing and time effects poorly, as their workflow does not stem directly from a timeline, as do layer-based compositing packages. Software which incorporates a node based interface include Natron, Shake, Blender, Blackmagic Fusion, and Nuke. Nodes are a great way to organize the effects in a complex shot while maintaining a grip on the smaller details.

Layer-based compositing represents each media object in a composite as a separate layer within a timeline, each with its own time bounds, effects, and keyframes. All the layers are stacked, one above the next, in any desired order; and the bottom layer is usually rendered as a base in the resultant image, with each higher layer being progressively rendered on top of the previously composited of layers, moving upward until all layers have been rendered into the final composite. Layer-based compositing is very well suited for rapid 2D and limited 3D effects, such as in motion graphics, but becomes awkward for more complex composites entailing numerous layers. A partial solution to this is some programs' ability to view the composite-order of elements (such as images, effects, or other attributes) with a visual diagram called a flowchart to nest compositions, or "comps," directly into other compositions, thereby adding complexity to the render-order by first compositing layers in the beginning composition, then combining that resultant image with the layered images from the proceeding composition, and so on.

See also

Further reading

  • Mansi Sharma; Santanu Chaudhury; Brejesh Lall (2014). Content-aware seamless stereoscopic 3D compositing. Proceedings of the 2014 Indian Conference on Computer Vision Graphics and Image Processing, ACM New York, NY, USA. doi:10.1145/2683483.2683555.
  • T. Porter and T. Duff, "Compositing Digital Images", Proceedings of SIGGRAPH '84, 18 (1984).
  • The Art and Science of Digital Compositing (ISBN 0-12-133960-2)
  • Samuel Collett, "Node Based Compositing Explained(Video)" (2023)

Read other articles:

Nicola Leali Informasi pribadiNama lengkap Nicola LealiTanggal lahir 17 Februari 1993 (umur 31)Tempat lahir Castiglione delle Stiviere, ItalyTinggi 1,88 m (6 ft 2 in)Posisi bermain GoalkeeperInformasi klubKlub saat ini Cesena (pinjaman dari Juventus)Nomor 1Karier junior2003–2011 BresciaKarier senior*Tahun Tim Tampil (Gol)2011–2012 Brescia 17 (0)2012– Juventus 0 (0)2012–2013 →Lanciano (pinjaman) 37 (0)2013–2014 →Spezia (pinjaman) 38 (0)2014– →Cesena (pinj...

 

 

Artikel ini sebatang kara, artinya tidak ada artikel lain yang memiliki pranala balik ke halaman ini.Bantulah menambah pranala ke artikel ini dari artikel yang berhubungan atau coba peralatan pencari pranala.Tag ini diberikan pada Desember 2022. Edhie dapat merujuk pada: Sarwo Edhie Wibowo (1925–1989), tentara Indonesia. Pramono Edhie Wibowo (1955–2020), tentara Indonesia. Hartanto Edhie Wibowo (lahir 1969), politikus Indonesia. Edhie Baskoro Yudhoyono (lahir 1980), politikus Indonesia. I...

 

 

  لاتحاد في فترة لاحقة، طالع اتحاد الجمهوريات العربية. اتفق العراق ومصر وسوريا بالفعل على العلم المشترك في العام 1963. لقد ألغت سوريا هذا العلم في العام 1972 فيما لم تعتمده مصر أبدًا في مارس 1972، اقترح العراق على مصر وسوريا إعادة تأسيس الجمهورية العربية المتحدة التي سقطت في...

Disambiguazione – Se stai cercando altri significati, vedi Coppa del Re 2013-2014 (disambigua). Copa del Rey 2013-2014 Competizione Copa del Rey Sport Calcio Edizione 112ª Organizzatore FEF Date dal 4 settembre 2013al 16 aprile 2014 Luogo  Spagna Partecipanti 84 Risultati Vincitore Real Madrid(19º titolo) Secondo Barcellona Semi-finalisti Atlético MadridReal Sociedad Statistiche Miglior marcatore Lionel Messi (5) Incontri disputati 112 Gol segnati 278 (2,48 per in...

 

 

Campo di Villa ChayesCampo di San Jacopo Il campo di Villa Chayes nella sfida tra Pro Vercelli e Bologna (2-1) valevole per la finale del torneo settentrionale, 17 luglio 1921. Informazioni generaliStato Italia UbicazioneViale Regina Margherita, Livorno Inizio lavori1915 Inaugurazione1915 Chiusura1933 ProprietarioComune di Livorno Informazioni tecnichePosti a sedereCirca 4 000 su 6 000 totali[1]. CoperturaTribuna coperta Mat. del terrenoErba Dim. del terreno95 x 60 m[2] U...

 

 

Vladimir AntonovВладимир АнтоновAntonov, circa 1905NationalityRussianOccupationArchitectBuildingsZanaetchiski Dom Banovinska Gradska Bolnica Sokolana Hotel Kumanovo Church, Holy Trinity Gradski Park Church, Holy Trinity Vladimir Antonov (Macedonian: Владимир Антонов) was a Russian architect who worked for most of his career in Kumanovo, Macedonia in the beginning of the 20th century.[1][2][3] He was a member of the White Guardians and beca...

Feux d'artifice au SkyDome de Toronto après la victoire en Série mondiale des Blue Jays le 23 octobre 1993. La Série mondiale 1993 était la 90e série finale des Ligues majeures de baseball. Elle a débuté le 16 octobre 1993 et opposait les champions de la Ligue américaine et champions en titre du baseball, les Blue Jays de Toronto, aux champions de la Ligue nationale, les Phillies de Philadelphie. Cette série 4 de 7 s'est terminée le 23 octobre 1993 par une victoire des Blue Jay...

 

 

College football bowl game College football game2018 Lockheed Martin Armed Forces Bowl16th Armed Forces Bowl Houston Cougars Army Black Knights (8–4) (10–2) The American Independent 14 70 Head coach: Major Applewhite Head coach: Jeff Monken APCoaches 2225 1234 Total Houston 0707 14 Army 14281414 70 DateDecember 22, 2018Season2018StadiumAmon G. Carter StadiumLocationFort Worth, TexasMVPKelvin Hopkins (QB, Army) & Romello Brooker (TE, Houston)[1]FavoriteArmy ...

 

 

Cet article est une ébauche concernant Los Angeles. Vous pouvez partager vos connaissances en l’améliorant (comment ?) selon les recommandations des projets correspondants. Beverly GroveGéographiePays  États-UnisÉtat CalifornieComté comté de Los AngelesCharter city Los AngelesSuperficie 4,27 km2Coordonnées 34° 04′ 25″ N, 118° 22′ 36″ ODémographiePopulation 21 417 hab. (2000)Densité 5 015,7 hab./km2 (2000)Fonction...

  لمعانٍ أخرى، طالع بون (توضيح). بون     الإحداثيات 38°15′00″N 104°15′18″W / 38.25°N 104.255°W / 38.25; -104.255   تقسيم إداري  البلد الولايات المتحدة[1][2]  التقسيم الأعلى مقاطعة بويبلو  خصائص جغرافية  المساحة 0.961764 كيلومتر مربع0.961987 كيلومتر مربع (1 أبريل ...

 

 

Hitler bersama dengan Ernst Hanfstaengl dan Hermann Göring, pada 21 Juni 1932. Kenaikan Adolf Hitler dimulai di Jerman pada September 1919 saat Hitler bergabung dengan partai politik yang dikenal sebagai Deutsche Arbeiterpartei – DAP (Partai Buruh Jerman). Namanya diubah pada 1920 menjadi Nationalsozialistische Deutsche Arbeiterpartei – NSDAP (Partai Buruh Jerman Sosialis Nasional, umum dikenal sebagai Partai Nazi). Partai politik tersebut terbentuk dan berkembang pada era pasc...

 

 

 本表是動態列表,或許永遠不會完結。歡迎您參考可靠來源來查漏補缺。 潛伏於中華民國國軍中的中共間諜列表收錄根據公開資料來源,曾潛伏於中華民國國軍、被中國共產黨聲稱或承認,或者遭中華民國政府調查審判,為中華人民共和國和中國人民解放軍進行間諜行為的人物。以下列表以現今可查知時間為準,正確的間諜活動或洩漏機密時間可能早於或晚於以下所歸�...

Latvian politician and political scientist Marija GolubevaMinister of the InteriorIn office3 June 2021 – 16 May 2022Preceded bySandis ĢirģensSucceeded byArtis PabriksMember of 13th SaeimaIn officeNovember 6, 2018 – November 1, 2022Parliamentary groupDevelopment/For! Personal detailsBorn (1973-06-28) 28 June 1973 (age 50)Alma materUniversity of Latvia (BA)Central European University (MA)University of Cambridge (PhD)OccupationPoliticianPolitical scientistHistorian M...

 

 

Welsh theologian (1817–1870) Not to be confused with the archbishop and theologian Rowan Williams (born 1950). Rowland Williams Reverend Professor Rowland Williams Rowland Williams (16 August 1817 – 18 January 1870) was a Welsh theologian and educationalist. He was vice-principal and Professor of Hebrew at St David's College, Lampeter, from 1849 to 1862 and one of the most influential theologians of the nineteenth century. He supported biblical criticism and pioneered comparative reli...

 

 

当時の築地小劇場 築地小劇場跡の碑 (碑文は里見弴によるもの) 築地小劇場(つきじしょうげきじょう)は、土方与志と小山内薫が1924年(大正13年)6月13日に開設した新劇の常設劇場である。また、劇場付属の劇団の名称でもあった。 概要 所在地は、東京府東京市京橋区築地2丁目5番地。現在の東京メトロ日比谷線築地駅からほど近い、東京都中央区築地2丁目11番�...

У Вікіпедії є статті про інші значення цього терміна: 9-та армія. 9-та армія9. Armee Колона танків Panzer III перед початком операції «Цитадель». Червень 1943На службі 15 травня 1940 — 8 травня 1945Країна  Третій РейхНалежність  ВермахтВид  Сухопутні військаЧисельність польова...

 

 

  لمعانٍ أخرى، طالع الكنيسة الأثرية (توضيح). هذه المقالة يتيمة إذ تصل إليها مقالات أخرى قليلة جدًا. فضلًا، ساعد بإضافة وصلة إليها في مقالات متعلقة بها. (مارس 2023) الكنيسة الأثرية فرنانة تقديم البلد  تونس مدينة فرنانة نوع كنيسة الموقع الجغرافي تعديل مصدري - تعديل   ال�...

 

 

Национальный парк Амбоселиангл. Amboseli National Park Панорама парка Категория МСОП — II (Национальный парк) Основная информация Площадь392 км²  Дата основания1974 год  Посещаемость120 000 (оценка) (2006)  Управляющая организацияСлужба охраны дикой природы Кении Распол�...

Arlette Laguiller Arlette Laguiller en 2005. Fonctions Porte-parole de Lutte ouvrière 1973 – 8 décembre 2008(35 ans) Prédécesseur Fonction créée Successeur Nathalie Arthaud Députée européenne 20 juillet 1999 – 19 juillet 2004(4 ans, 11 mois et 29 jours) Élection 13 juin 1999 Circonscription France Législature 5e Groupe politique GUE/NGL Conseillère régionale d'Île-de-France 23 mars 1998 – 28 mars 2004(6 ans et 5 jours) Élection 15 mars 1998 ...

 

 

1966 film of Raj Kapoor Teesri KasamTheatrical PosterDirected byBasu BhattacharyaScreenplay byNabendu GhoshPhanishwar Nath Renu (Dialogue)Story byPhanishwar Nath Renu[1]Based on Maare Gaye Gulfamby Phanishwar Nath RenuProduced byShailendraStarringRaj KapoorWaheeda RehmanRehanaCinematographySubrata Mitra[1]Edited byIqbalMusic byShankar-JaikishenShailendra (Lyrics)Hasrat Jaipuri (Lyrics)ProductioncompanyImage MakersRelease date 1966 (1966) Running time159 minCountryIndiaLan...