1. A method of estimating the noise in a digital image for use in subsequent image processing, comprising the steps of: a) receiving a source digital image having a plurality of pixels; b) selecting a pixel of interest; c) providing a plurality of orientations for the pixel of interest; d) using gradient analysis on the source digital image and the plurality of orientations to select the most suitable orientation for estimating noise for the pixel of interest; e) using the selected orientation in the pixel of interest to determine a noise-free pixel estimate for the pixel of interest; and f) repeating steps b)-e) for other pixels of interest and using the noise-free pixel estimates to calculate a noise characteristic value representing the noise estimate for the source digital image.