1. Method for forming a model for improving image quality of a digital image captured with an imaging module comprising at least an imaging optics and an image sensor, where the image is formed through the imaging optics onto the light sensitive image sensor, the method comprising: determining a vignetting effect of the digital image captured with the imaging module for at least two of plural primary color components of the imaging module, formulating vignetting models for said at least two primary color components of said imaging module, and combining said vignetting models into a single correction function defined using correction coefficients, the correction function defining a correction gain for different points (x,y) of the image.