The independent pixel approximation (IPA), which treats radiative properties of each pixel independently using standard plane-parallel calculations, preserves scale-invariance found in the analyses of the horizontal variability of liquid water in marine stratocumulus clouds. Several studies however report a violation of scale-invariance in Landsat cloud radiance fields which are much smoother than cloud structure on small scales. This shows a limitation of IPA on small scales: it is unable to simulate the smooth small-scale behavior which is due to the horizontal photon transport. This paper introduces a ÒnonlocalÓ independent pixel approximation (NIPA) which extends the IPA by incorporating empirically the smoothing effects of horizontal interpixel fluxes. It also treats the inverse problem of cloud optical depth retrieval from satellite data, showing how NIPA can be used to overcome the limitations of current IPA-based methods at small scales.