There is provided a method and corresponding device for noise generated by absorption of x-ray photons in an image sensor having a number of pixels. The method is based on identifying (S1) so-called hot pixels affected by absorption of x-rays, and calculating (S2), for each hot pixel, directional gradients in a number of different directions in a pixel neighborhood of the hot pixel. The method further involves selecting (S3), for each hot pixel, at least one direction among those directions having lowest gradient, and determining (S4), for each hot pixel, a replacement value based on neighborhood pixel values in the selected direction(s). For each hot pixel, the value of the hot pixel is then replaced (S5) with the determined replacement value. In this way, noise generated by the absorption of x-ray photons in the image sensor may be reduced, while substantially maintaining the resolution (sharpness) in the image.