A method and an apparatus for changing the brightness of an image are provided. The method for changing the brightness of an image includes obtaining a level incremental rate, which denotes the degree to which the brightness of three input color components, i.e., first, second and third color components, will be increased according to a determined color gamut, scaling the input color components using the level incremental rate and determining the results of the scaling as incremental values of the input color components, obtaining a fourth color component value using the incremental values, and obtaining output color components, the brightnesses of which are increased from those of the input color components, using the fourth color component value and the incremental values.