An image conversion unit (100) for converting an input image (602) into an output image (606) is disclosed. The image conversion unit (100) comprises: a filter (104) for selecting a group of connected input pixels from the input image (602), the group of connected input pixels having a size which is relatively small relative to the size of the input image (602), the input pixels of the group of connected input pixels having high luminance values relative to the range of input luminance values; and a pixel processor (104) for assigning luminance values to output pixels of the output image (606) on basis of the respective luminance values of the input pixels of the input image (602), whereby the luminance values of the output pixels corresponding to the group of connected input pixels are higher than the respective luminance values of the connected input pixels.