The fact that B and R are close to a U axis and to a V axis, respectively, is noted. On that basis, from an example of color adjustment parameters set in directions of colors, it is found out that, when inputted V is in a negative range, B has a small influence. Accordingly, a B component is omitted from calculation in order to reduce a calculation amount. Similarly, components having small influences are omitted when B is in a positive range, when U is in the positive range, and when U is in the negative range. Thereby, adjustment parameters AR, AG, and AB set in directions shown in the drawing can be defined. When inputted V is in the positive range, a V component can be adjusted by multiplying AR by the inputted V. Similar processing is performed when inputted V is in the negative range, when U is in the positive range, and when U is the negative range, respectively. With this taken into consideration by setting values of the adjustment parameters for respective RGB larger than 1 or smaller than 1, color transformation processing for adjusting darkness/lightness of colors can be performed, independently of brightness, so as to bring values of U and V close toward a color component to be increase in intensity. This allows reduction in load of color transformation processing.