1. An imaging apparatus including an infrared video camera comprising a sensor array and operable to produce successive video images in the form of pixelated two-dimensional images, the imaging apparatus further comprising a processing arrangement operable to reduce or increase an overall brightness of an enhanced image in dependence upon an overall brightness of a pre-enhanced image and an overall brightness of a preceding enhanced image, so that a change in the overall brightness between the enhanced image and the preceding enhanced image is decreased to be less than a difference in overall brightness between the pre-enhanced image and the preceding enhanced image.