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Basically filtering was happening twice, first time by applying weights of EWA
filter itself and then by applying subpixel offset while reading pixel values.
EWA sampling is designed for downsampling images, i.e. scaling down the size of
input image pixels, which happens regularly in compositing. While the standard
sampling methods (linear, cubic) work reasonably well for linear
transformations, they don't yield good results in non-linear cases like
perspective projection or arbitrary displacement. EWA sampling is comparable to
mipmapping, but avoids problems with discontinuities.
To work correctly the EWA algorithm needs partial derivatives of the mapping
functions which convert output pixel coordinates back into the input image
space (2x2 Jacobian matrix). With these derivatives the EWA algorithm
projects ellipses into the input space and accumulates colors over their
area. This calculation was not done correctly in the compositor, only the
derivatives du/dx and dv/dy were calculation, basically this means it only
worked for non-rotated input images.
The patch introduces full derivative calculations du/dx, du/dy, dv/dx, dv/dy for
the 3 nodes which use EWA sampling currently: PlaneTrackWarp, MapUV and
Displace. In addition the calculation of ellipsis area and axis-aligned
bounding boxes has been fixed.
For the MapUV and Displace nodes the derivatives have to be estimated by
evaluating the UV/displacement inputs with 1-pixel offsets, which can still have
problems on discontinuities and sub-pixel variations. These potential problems
can only be alleviated by more radical design changes in the compositor
functions, which are out of scope for now. Basically the values passed to the
UV/Displacement inputs would need to be associated with their 1st order
derivatives, which requires a general approach to derivatives in all nodes.
Distinguish the 3 different methods for acquiring pixel color values (executePixel, executePixelSampled, executePixelFiltered).
This makes it easier to keep track of the different sampling methods (and works nicer with IDEs that do code parsing).
Differential Revision: http://developer.blender.org/D7
`````|````` | | | ..''''
| | | |______ .''
| | | | ..'
| | |_______ |___________ ....''
merge to TRUNK!
* The old compositor is still available (Debug Menu: 200)
This commit was brought to you by:
Developers:
* Monique Dewanchand
* Jeroen Bakker
* Dalai Felinto
* Lukas Tönne
Review:
* Brecht van Lommel
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* Nate Wiebe
* Wolfgang Faehnle
* Carlo Andreacchio
* Daniel Salazar
* Artur Mag
* Christian Krupa
* Francesco Siddi
* Dan McGrath
* Bassam Kurdali
But mostly by the community:
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Michael Tiemann
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Blender Guru
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Olaf Beckman
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Kajimba
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Film Works
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Blender 3D Graphics and Animation
Henk Vostermans
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BlenderDay/2011
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Jérôme Scaillet
Bronze (Ivo Grigull, Dylan Urquidi, Philippe Derungs, Phil Beauchamp, Bruce Parrott, Mathieu Quiblier, Daniel Martinez, Leandro Inocencio, Lluc Romaní Brasó,
Jonathan Williamson, Michael Ehlen, Karlis Stigis, Dreamsteep, Martin Lindelöf, Filippo Saracino, Douwe van der Veen, Olli Äkräs, Bruno D'Arcangeli,
Francisco Sedrez Warmling, Watchmike.ca, peter lener, Matteo Novellino, Martin Kirsch, Austars Schnore, KC Elliott, Massimiliano Puliero, Karl Stein,
Wood Design Studios, Omer Khan, Jyrki Kanto, Michał Krupa, Lars Brubaker, Neil Richmond, Adam Kalisz, Robert Garlington, Ian Wilson, Carlo Andreacchio,
Jeremias Boos, Robert Holcomb, Gabriel Zöller, Robert Cude, Natibel de Leon, Nathan Turnage, Nicolas Vergnes, Philipp Kleinhenz, Norman Hartig, Louis Kreusel,
Christopher Taylor, Giovanni Remondini, Daniel Rentzsch, Nico Partipilo, Thomas Ventresco, Johannes Schwarz, Александр Коротеев, Brendon Harvey,
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Philipp Oeser, Daniel Thul, Thobias Johansson, Mauro Bonecchi, Georg Piorczynski, Sebastian Michailidis, L M Weedy, Gen X, Stefan Hinze, Nicolò Zubbini,
Erik Pusch, Rob Scott, Florian Koch, Charles Razack, Adrian Baker, Oliver Villar Diz, David Revoy, Julio Iglesias Lopez, Coen Spoor, Carlos Folch,
Joseph Christie, Victor Hernández García, David Mcsween, James Finnerty, Cory Kruckenberg, Giacomo Graziosi, Olivier Saraja, Lars Brubaker, Eric Hudson,
Johannes Schwarz, David Elguea, Marcus Schulderinsky, Karel De Bruijn, Lucas van Wijngaarden, Stefano Ciarrocchi, Mehmet Eribol, Thomas Berglund, Zuofei Song,
Dylan Urquidi )
