An optical low pass filter or blur filter, and method of making the filters, using an article having a birefringent surface for refracting incoming light when used with an image sensor. The birefringent surface of the article, such as a film, is structured or tilted such that, when the blur filter is placed within an optical path between a lens and the image sensor, the birefringent surface causes refraction of a light signal in the optical path into multiple light signals each being incident upon different sub-pixels within the pixels in the image sensor to prevent or reduce artifacts, such as undesirable color moiré effects, in the resulting digital image. The structures on the surface have a variable pitch or angles. The variable pitch can include a periodic, aperiodic, or quasi-aperiodic pitch, to reduce diffractive artifacts in the resulting image.