1. An image conversion unit ( 100 ) for converting an input image ( 602 ) into an output image ( 606 ), comprising: 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.