Lukas Tönne
67134a7bf6
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.
69 lines
1.9 KiB
C++
69 lines
1.9 KiB
C++
/*
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* Copyright 2011, Blender Foundation.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*
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* Contributor:
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* Dalai Felinto
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*/
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#ifndef _COM_DisplaceOperation_h
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#define _COM_DisplaceOperation_h
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#include "COM_NodeOperation.h"
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class DisplaceOperation : public NodeOperation {
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private:
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/**
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* Cached reference to the inputProgram
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*/
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SocketReader *m_inputColorProgram;
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SocketReader *m_inputVectorProgram;
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SocketReader *m_inputScaleXProgram;
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SocketReader *m_inputScaleYProgram;
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float m_width_x4;
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float m_height_x4;
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public:
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DisplaceOperation();
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/**
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* we need a 2x2 differential filter for Vector Input and full buffer for the image
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*/
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bool determineDependingAreaOfInterest(rcti *input, ReadBufferOperation *readOperation, rcti *output);
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/**
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* the inner loop of this program
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*/
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void executePixelSampled(float output[4], float x, float y, PixelSampler sampler);
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void pixelTransform(const float xy[2], float r_uv[2], float r_deriv[2][2]);
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/**
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* Initialize the execution
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*/
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void initExecution();
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/**
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* Deinitialize the execution
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*/
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void deinitExecution();
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private:
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bool read_displacement(float x, float y, float xscale, float yscale, const float origin[2], float &r_u, float &r_v);
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};
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#endif
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