An apparatus has first and second generation units which generate, from input image data, color component data for luminance output and color component for color difference output, first and second convertors which converts tones of each piece of the color component data for luminance output and for color difference output, a combining unit combining each piece of the color component data obtained by the first and second convertors to generate respective pieces of combined color component data; a separation unit respectively separating luminance data and color difference data from the combined color component data; and a correction unit correcting a tone of each of the luminance data and color difference data. The second convertor has a characteristic for outputting a non-negative value in a range, of negative infinity to a positive threshold set in advance.