The paper demonstrates a method of simultaneously testing the spatial and tonal resolution of a camera. Unlike the modulation transfer function which has been used in the past, the measure proposed rates the resolution as a single number rather than a response over varied resolution, simplifying the measure and making it possible to compare the performance of different camera cameras easily. Previous work was subject to perturbations caused by aliasing at high frequencies. The measure proposed is immune to such perturbations, and is therefore appropriate for measuring a wide range of image sensing systems.