1. A method of applying defective pixel fixing to image data, the image data comprising pixel values for a regular array of pixels in a plurality of colour channels, wherein the method comprises, for a target pixel in a target colour channel: for each of a plurality of directions which intercept the target pixel: (a) determining a gradient of pixel values in one of said colour channels along said direction; and (b) determining a candidate value for the target pixel using: (i) the determined gradient, and (ii) a pixel value of a pixel in the target colour channel which is aligned with the target pixel along said direction; determining a predicted value for the target pixel using the plurality of candidate values determined for the respective plurality of directions; determining whether the target pixel is characteristic of a defective pixel based on the similarity of the target pixel value and the predicted value; and selectively replacing the target pixel value with the predicted value based on the determination as to whether the target pixel is characteristic of a defective pixel.