An image processing device for converting input image data in input color space into output image data in output color space comprises an input unit configured to input a plurality of input pixel signals comprising the input image data, a designation unit configured to designate an achromatic condition for pixels corresponding to the plurality of input pixel signals, and an achromatic judgment unit configured to judge whether or not each of the plurality of input pixel signals input by the input unit satisfies the achromatic condition, wherein the achromatic judgment unit judges that a pixel which corresponds to a particular input pixel signal is an achromatic pixel where the particular input pixel signal satisfies the achromatic condition.