This invention relates to a method for improving image quality of a digital image captured with an imaging module comprising at least imaging optics and an image sensor, where the image is formed through the imaging optics, the image consisting of at least one colour component. In the method, the degradation information of each colour component of the image is found and is used for improving image quality. The degradation information of each colour component is specified by a point-spread function. Each colour component is restored by the degradation function. The image can be unprocessed image data. The invention also relates to several alternatives for implementing the restoration, and for controlling and regularizing the inverse process independently of the image degradation. The invention also relates to a device, to a module, to a system and to a computer program products and to a program modules.