Soft adaptive gradient angle interpolation of grayscale images

We introduce a new edge-directed interpolator based on locally defined, straight line approximations to image isophotes. The first spatial derivatives of image intensity are used to describe the behavior of pixel-intersecting isophotes in terms of their slopes. Slopes are determined by inverting a tridiagonal matrix and are forced to vary linearly from pixel to pixel. Image resizing is performed using standard, 1D interpolators along the approximated isophotes. The proposed method can accommodate arbitrary scaling factors, provides state-of-the-art results in terms of PSNR as well as other quantitative quality metrics, and has the advantage of computational complexity that is directly proportional to the number of pixels.