Moiré patterns are undesirable artifacts in printing applications. Sampling moiré is caused by aliasing due to image resampling from one lattice to another. In color printing each color separation uses its own halftone lattice. Therefore, moiré patterns display an unexpected new frequency and orientation, but also influence the color appearance itself. These artifacts are frequently encountered in commercial (even high quality) printing since the interpolation algorithms used in RIPs are fairly simple (e.g., bilinear interpolation). Additionally, high-resolution images become everyday fare which increases the chance of highfrequency components and so moiré patterns. Approaches such as simple low-pass filtering unacceptably blurs the edges, while manual smoothing by an operator is very time-consuming.This paper proposes an optimal prefilter which is based on a least-squares resampling technique. Such an approach requires a suitable discrete/continuous model and computes the reconstruction function which minimizes the error between the continuous representations of the images on the source and target lattice. The reconstruction function jointly takes into account the Nyquist areas of the color separations and can be used as an optimal prefilter before halftoning. Experimental results show that after prefiltering, the images are much less prone to moiré and look as sharp as without prefiltering.