Abstract: A method and system for selectively transforming a spatially varying optical characteristic (F) of an image in a pixel array. The pixel array is segmented into stripes of contiguous rows. A two-dimensional convolution C(x, y) of F is determined at only selected pixels (x, y). C(x, y) is a function of a product of a horizontal kernel h(x) and a vertical kernel v(y). Determining C(x, y) at each selected pixel (x, y) includes determining n vertical convolutions, wherein each vertical convolution is equal to a scalar product of F and v(y) in a kernel space surrounding (x,y), forming an array (V) from the n vertical convolutions, and computing C(x,y) as a scalar product of V and a constant horizontal vector (H) formed from h(x). The stripes are collected to form a transformed image which is stored and/or displayed. A cache facilitates selective reuse of vertical convolutions for determining C(x,y).