Method of generating combined look-up table, and image processing apparatus and image forming apparatus

A method of generating a combined look-up table based on first and second look-up tables wherein:

• each of the first, second, and combined look-up tables includes a plurality of grid-point data, and each of the plurality of grid-point data includes an input value and an output value corresponding to the input value;
• the first look-up table is a table for converting a first color component data represented in a first color space into a second color component data represented in the first color space;
• the second look-up table is a table for converting the second color component data into a third color component data represented in a second color space;
• the combined look-up table is a table for converting the first color component data into the third color component data;
• and
• the method comprises:
• a calculating step of calculating an input value of the combined look-up table so that the calculated input value is input to the first look-up table, and an output value is output which corresponds to the input value of one of grid-point data of the second look-up table;
• and
• a setting step of setting an output value for grid-point data of the combined look-up table by using the output value of said one of grid-point data of the second look-up table, and setting an input value for the grid-point data of the combined look-up table by using the input value calculated in the calculating step.