A method of processing an image includes a region of a highway in front of the vehicle captured using an imager having a two dimensional array of image capturing pixels. The array includes a first set of pixels substantially independent of hue and a second set of pixels dependent of a limited range of hues. The method further includes the steps of producing a first image where each pixel is assigned a value derived from the first set of pixels and producing a second image where each pixel is assigned a value derived from the first set of pixels and the second set of pixels. The method includes identifying-for at least one pixel in the first image a first intensity change value indicative of the difference between that pixel and at least one adjacent pixel identifying for a corresponding pixel in the second image a second intensity change value indicative of the difference between that pixel and at least one adjacent pixel. A combined image is formed using a defined set of combination rules to assign a value to the corresponding pixel in the combined image which depends on the first and second identified intensity change values for that corresponding pixel.