Any projection of a 3D scene into a wide-angle image unavoidably results in distortion. Current projection methods either bend straight lines in the scene, or locally distort the shapes of scene objects. We present a method that minimizes this distortion by adapting the projection to content in the scene, such as salient scene regions and lines, in order to preserve their shape. Our optimization technique computes a spatially-varying projection that respects user-specified constraints while minimizing a set of energy terms that measure wide-angle image distortion. We demonstrate the effectiveness of our approach by showing results on a variety of wide-angle photographs, as well as comparisons to standard projections.

/pdf/optimizing-content-preserving-projections-for-wide-angle-40rmgbqk1i.pdf

Optimizing content-preserving projections for wide-angle images

Pictures taken by a rotating camera cover the viewing sphere surrounding the center of rotation. Having a set of images registered and blended on the sphere what is left to be done, in order to obtain a flat panorama, is projecting the spherical image onto a picture plane. This step is unfortunately not obvious - the surface of the sphere may not be flattened onto a page without some form of distortion. The objective of this paper is discussing the difficulties and opportunities that are connected to the projection from viewing sphere to image plane. We first explore a number of alternatives to the commonly used linear perspective projection. These are 'global' projections and do not depend on image content. We then show that multiple projections may coexist successfully in the same mosaic: these projections are chosen locally and depend on what is present in the pictures. We show that such multi-view projections can produce more compelling results than the global projections

/pdf/squaring-the-circle-in-panoramas-23db68ogqz.pdf

Squaring the circle in panoramas

Various types of video can be captured with fisheye lenses; their wide field of view is particularly suited to surveillance video. However, fisheye lenses introduce distortion, and this changes as objects in the scene move, making fisheye video difficult to interpret. Current still fisheye image correction methods are either limited to small angles of view, or are strongly content dependent, and therefore unsuitable for processing video streams. We present an efficient and robust scheme for fisheye video correction, which minimizes time-varying distortion and preserves salient content in a coherent manner. Our optimization process is controlled by user annotation, and takes into account a wide set of measures addressing different aspects of natural scene appearance. Each is represented as a quadratic term in an energy minimization problem, leading to a closed-form solution via a sparse linear system. We illustrate our method with a range of examples, demonstrating coherent natural-looking video output. The visual quality of individual frames is comparable to those produced by state-of-the-art methods for fisheye still photograph correction.

/pdf/fisheye-video-correction-3y90zpvzlp.pdf

Fisheye Video Correction

Works of art possess what we may call nominal authenticity, defined simply as the correct identification of the origins, authorship, or provenance of an object, ensuring that an object of aesthetic experience is properly named. However, the concept of authenticity often connotes something else, having to do with an object’s character as a true expression of an individual’s or a society’s values and beliefs. This second sense of authenticity can be called expressive authenticity. The following discussion will summarize some of the problems surrounding nominal authenticity and will conclude with a general examination of expressive authenticity. This paper is excerpted from a longer version published in the Oxford Handbook of Aesthetics.

Albert Flocon

Papers

Curvilinear Perspective: From Visual Space to the Constructed Image

La perspective curviligne : de l'espace visuel à l'image construite