Sharp image interpolation by mapping level curves
Hiep Quang Luong, Wilfried R. Philips · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2005
In this paper we describe a novel approach to image interpolation while preserving sharp edge information. Many interpolation methods already have been proposed in the literature, but suffer from one or more artifacts such as aliasing, blurring, ringing etc. Non-linear methods or edge-directed methods result in sharp interpolated images but often look segmented or have great visual degradation in fine structured textures. We concentrate in this paper on tackling blurred edges by mapping the image's level curves. Image's level curves or isophotes are spatial curves with a constant intensity level. The mapping of these intensity levels can be seen as a local contrast enhancement problem, therefore we can rely on some contrast enhancement techniques. A great advantage of this approach is that the shape of the level curves (and of the objects) are preserved and no explicit edge detection is needed here. Additional constraints in function of the image interpolation are defined in this flexible framework. Different strategies of extending greyscale interpolation to colour images are also discussed in this paper. The results show a large improvement in visual quality: the edges are sharper and ringing effects are removed.