A method for determining whether a image pixel of an image comprising a plurality of image pixels generated from a pixel array of an image sensor, each having an image pixel value formed from a respective reset level, has suffered a darkening resulting from a drop in its reset level prior to sampling due to a high intensity illumination. Where a first image pixel has its reset level detected to have crossed a threshold and a second image pixel is saturated, a third image pixel between the first and second image pixels is determined to have suffered such darkening if it is not saturated and if no intervening image pixel between the first and the third image pixels either is saturated or is generated from a reset level detected to have crossed a threshold. The crossing of the reset level may be signaled by a reserved codeword.