In his seminal paper "Early Processing of Visual Information,” David Marr introduced the primal sketch concept as a rich multiscale representation of "significant” intensity changes. The goal of building that primal sketch is, to date, unrealized. We have extended the concept to apply to significant changes in other important representations of visual information, specifically curvature changes along planar curves and surface changes in range maps. We have performed preliminary investigations of the primal sketch of intensity changes. In each case, we introduce a set of parametrized discontinuities as primitives and derive expressions for their convolutions with the first and second derivatives of a Gaussian. We derive symbolic signatures for each primitive and describe implemented algorithms that discover instances of the primitives. Applications of the resulting representations are sketched.