Correcting defects in an image

1. A method of correcting defects in a representation of an image, using an image processor, comprising the steps in the image processor of identifying pixels at the periphery of a region of the image, to which region an image correction process has been applied; evaluating a gradient measure at said pixels at the periphery; accumulating said gradient measure along the periphery to form a periphery gradient measure and controlling the application of said image correction process to that region in accordance with the periphery gradient measure in which the said periphery gradient measure is evaluated for a corrected image region and for the same region of the same image without correction and the application of image correction to that region is controlled by the result of a comparison between the said periphery gradient measure with and without correction.

2. A method according to claim 1 in which the said image correction process is inhibited in regions where the said periphery gradient measure for a corrected image would be higher than the said periphery gradient measure for the same region in the uncorrected image.

3. A method according to claim 1 in which the said periphery gradient measure is a sum along the periphery of pixel value magnitude differences between pixels at the edge of the said region and respective adjacent pixels outside the said region.

4. A method according to claim 1 in which the said correction process is a process that corrects artefacts due to film dirt.

5. Apparatus for correcting defects in a representation of an image, the apparatus comprising an image correction unit receiving an image input; a periphery analysis unit for identifying the periphery of a region of the image which has been corrected in the image correction unit and for evaluating a periphery gradient measure for said region with and without correction, in which the application of correction to that region in an image output is controlled by the result of a comparison between the said measure with correction and the said measure without correction.

6. Apparatus according to claim 5 in which the said image correction unit is inhibited in regions where the said periphery gradient measure for a corrected image would be higher than the said measure for the same region in the uncorrected image.

7. Apparatus according to claim 5 in which the said periphery gradient measure is a sum along the periphery of pixel value magnitude differences between pixels at the edge of the said region and respective adjacent pixels outside the said region.

8. Apparatus according to claim 5 in which the said correction process is a process that corrects artefacts due to film dirt.

9. A non-transitory computer program product comprising instructions adapted to cause programmable apparatus to implement a method comprising the steps of provisionally correcting a region of an image to remove dirt or other defect; evaluating an accumulated gradient measure along the periphery of the region with and without correction; and choosing whether or not to use the corrected region depending on a comparison of the gradient measures.