212:
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438:, 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.
466:, 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.
33:
496:, 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
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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
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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
354:") 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.
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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
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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
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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.
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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.
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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
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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
434:, 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
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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.
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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.
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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
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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
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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
299:, 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:
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283:α, the opacity value of the foreground pixel. (α = 1 for an opaque foreground, α = 0 for a completely transparent foreground). A monochrome
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from the corresponding pixels from the two input images and recording the result in a third image, which is called the composited image.
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628:. Proceedings of the 2014 Indian Conference on Computer Vision Graphics and Image Processing, ACM New York, NY, USA.
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There are two radically different digital compositing workflows: node-based compositing and layer-based compositing.
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If all layers of an image change regularly but many layers still need to be composited (such as in
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By simply rewriting the mathematical expression, one can save 50% of the multiplications required.
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The most historically significant nonlinear compositing system was the
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Simplified online digital compositor to create a photomontage.
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or screen display. It is the digital analogue of optical film
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value, 'α', is used to control the proportions of two input
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The basic operation used in digital compositing is known as
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Node-based compositing represents an entire composite as a
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Mansi Sharma; Santanu
Chaudhury; Brejesh Lall (2014).
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may be too technical for most readers to understand
625:Content-aware seamless stereoscopic 3D compositing
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500:). Node-based compositing packages often handle
222:is the process of digitally assembling multiple
150:but its sources remain unclear because it lacks
647:, "Compositing Digital Images", Proceedings of
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654:The Art and Science of Digital Compositing (
226:to make a final image, typically for print,
61:Learn how and when to remove these messages
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258:values that end up a single output pixel.
215:Four images assembled into one final image
199:Learn how and when to remove this message
181:Learn how and when to remove this message
111:Learn how and when to remove this message
95:, without removing the technical details.
667:Node Based Compositing Explained(Video)"
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789:Autodesk Inferno, Flame and Flint (IFF)
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485:Node-based and layer-based compositing
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42:This article has multiple issues.
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50:or discuss these issues on the
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577:Digital on-screen graphic
275:a composited adetpixel, c
136:This article includes a
634:10.1145/2683483.2683555
265:Consider three pixels;
165:more precise citations.
494:directed acyclic graph
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597:Motion graphic design
443:distributed rendering
272:a background pixel, b
269:a foreground pixel, f
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951:Compositing software
885:Avid Elastic Reality
774:Left Angle Autograph
713:Free and open-source
587:Graphics coordinator
417:Algebraic properties
18:Compositing software
895:Avid Media Illusion
769:Adobe After Effects
704:Digital compositing
220:Digital compositing
910:Pinnacle Commotion
865:Autodesk Softimage
609:Digital Compositor
557:Broadcast designer
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138:list of references
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479:colour correction
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779:Apple Motion
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809:Saber (ILM)
481:of images.
447:parallelism
436:associative
428:commutative
369:+ (1 − α) b
339:+ (1 − α) b
325:+ (1 − α) b
311:+ (1 − α) b
250:, where an
242:Mathematics
232:compositing
163:introducing
935:Categories
562:Chroma key
502:keyframing
475:retouching
430:, such as
101:April 2012
47:improve it
726:Cinelerra
641:T. Porter
544:flowchart
498:composite
53:talk page
746:OpenShot
731:Kdenlive
706:software
649:SIGGRAPH
551:See also
530:rendered
454:Software
348:aliasing
880:Avid DS
834:Piranha
824:Mistika
814:Houdini
751:Shotcut
721:Blender
645:T. Duff
514:Blender
471:scaling
352:jaggies
252:opacity
159:improve
87:Please
819:Fusion
736:Natron
669:(2023)
658:
520:, and
506:Natron
460:Cineon
401:+ α (f
224:images
920:Shake
741:Olive
510:Shake
464:Kodak
387:− α b
379:= α f
365:= α f
335:= α f
321:= α f
307:= α f
289:matte
279:and
256:pixel
144:, or
829:Nuke
656:ISBN
643:and
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477:and
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405:− b
397:= b
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