A field emission device has an improved structure in which electron emission from a cathode is enhanced through external light radiation. The composition is useful in oxidative processes for removing sulfur from gaseous hydrocarbons. The method includes determining a peak value corresponding to the analog signal based on the peak-to-average ratio. The rotatable tray contains a plurality of receptacles. A whitepoint value of each pixel in the image is determined by interpolating the determined whitepoint values of neighboring tiles.