Finish Adaptive Space Carving Anselmo A. Montenegro †, Marcelo Gattass ‡, Paulo Carvalho † and...

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Adaptive Space CarvingAdaptive Space CarvingAnselmo A. MontenegroAnselmo A. Montenegro††, Marcelo Gattass, Marcelo Gattass‡‡ , P, Paulo Carvalhoaulo Carvalho†† and Land Luiz Velhouiz Velho††

††[anselmo,lvelho,pcezar]@visgraf.impa.br, [anselmo,lvelho,pcezar]@visgraf.impa.br, ‡‡ mgattass@tecgraf.puc-rio.br mgattass@tecgraf.puc-rio.br

3D object reconstruction is one of the most investigated topics 3D object reconstruction is one of the most investigated topics in computer graphics and vision. Among different techniques, in computer graphics and vision. Among different techniques, image based reconstruction is considered one of the most image based reconstruction is considered one of the most promising as high quality digital cameras are becoming a promising as high quality digital cameras are becoming a commodity hardware.commodity hardware.

Problems with photometric approaches:Problems with photometric approaches:Registration and evaluation of Registration and evaluation of thousandsthousands of individual of individual elements.elements.

Solution: Solution: Registration based on projective texture mapping.Registration based on projective texture mapping.Photo-consitency evaluation done by GPU programmingPhoto-consitency evaluation done by GPU programming..

Volumetric carving is a very Volumetric carving is a very common technique use for common technique use for image based reconstruction. It image based reconstruction. It may use silhouette and/or may use silhouette and/or photometric information. photometric information. Silhouette based methods Silhouette based methods were successfully used in real-were successfully used in real-time reconstructions. This is time reconstructions. This is not the case when we consider not the case when we consider photometric approaches.photometric approaches.

Still some problems:Still some problems: Too much elementsToo much elements Memory wasteMemory waste

Solution:Solution:Hierarchical representation Hierarchical representation of scene spaceof scene spaceRefinement approachRefinement approachAdaptive CarvingAdaptive Carving

Background estimation

Camera calibration

Image capture

Object segmentation

Reconstruction by Adaptive

Space Carving

Fixed pre-calibrated cameras setupFixed pre-calibrated cameras setup

Calibration by model recongnition

Adaptive space carving:Adaptive space carving:

•Works on an octree representation of the scene space.Works on an octree representation of the scene space.

•The reconstruction is obtained by a refinement process based The reconstruction is obtained by a refinement process based on photo-consistency tests.on photo-consistency tests.

•Uses photometric and silhouette information in multiresolution to Uses photometric and silhouette information in multiresolution to detect coarse empty regions as soon as possible.detect coarse empty regions as soon as possible.

•Classification of the cells: Classification of the cells: CONSISTENT, INCONSISTENT and UNDEFINED.CONSISTENT, INCONSISTENT and UNDEFINED.

•Undefined cells are subdivided and classified in later stages.Undefined cells are subdivided and classified in later stages.

Level 5

Segmentation based on intervals of confidence

Adaptive Space CarvingAdaptive Space CarvingSpace CarvingSpace Carving

No cell subdivided ?

Last registration plane of the level?

Subdivide undefined cells and colorize photo-consistent cells. Update visibility maps.

Test the consistency of the non- classified cells intersected by the current registration plane

Project images on the current registration plane with resolution compatible to the octree level

AlgorithmAlgorithm Levels of refinementLevels of refinement

Level 6

Level7 Level 8

Zoom

Fixed cameras reconstruction resultsFixed cameras reconstruction results

Final considerationsFinal considerations

In this work we only explored convencional GPU hardware In this work we only explored convencional GPU hardware accelerated operations, as in the registration step by projective accelerated operations, as in the registration step by projective texture mapping . The mechanism of copying framebuffer texture mapping . The mechanism of copying framebuffer information to main memory introduces significant overhead to the information to main memory introduces significant overhead to the overall processing time. We believe that by combining our adaptive overall processing time. We believe that by combining our adaptive approach with photo-consistency test done by GPU programming approach with photo-consistency test done by GPU programming we can obtain considerable gains in efficiency. we can obtain considerable gains in efficiency.

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Determine the registration planes at the current level

Initialize the octree root cell with the bounding box of the scene

Images and

segmentation

Visibility and noise maps