1. A method of increasing the dynamic range of an image comprising a plurality of pixels each having a luminance value within a first luminance dynamic range, the method comprising: determining a background luminance value for each pixel of the image, determining a minimum and a maximum of the background luminance values, determining a conversion factor for each pixel of the image, wherein the conversion factor for each pixel is based on the minimum and maximum of the background luminance values, converting the image from the first luminance dynamic range to a second luminance dynamic range by multiplying the luminance value of each pixel of the image by its conversion factor.