Image forming apparatus adjusting concentration of gray with improved reference and test patterns

A method of adjusting a concentration of gray in a printed color image, comprising the steps of:

• producing reference concentration data, wherein said reference concentration data represents a predetermined reference concentration;
• producing adjustment concentration pattern data, wherein said adjustment concentration pattern data represents a plurality of concentrations within a predetermined concentration range, including the predetermined reference concentration;
• printing an adjustment sheet based on the reference pattern data and the adjustment concentration pattern data so that a reference pattern and a plurality of test patterns are printed on the adjustment sheet, wherein the reference pattern indicates the predetermined reference concentration and the test patterns indicate the concentrations indicated by the adjustment concentration pattern data;
• comparing a concentration of the reference pattern with the concentrations of the test patterns printed on the adjustment sheet to detect an adjustment concentration value;
• and
• adjusting concentration data of image data to be printed in accordance with an adjustment concentration value detected, wherein said reference concentration pattern data and adjustment concentration pattern data are arranged so that a color from the reference pattern and a color of the test pattern is added to another of the color of the test patterns.

A computer readable medium having computer readable code embodied therein for causing a computer to adjust a concentration of gray in a printed color image, comprising:

• code for producing reference concentration data, wherein said reference concentration data represents a predetermined reference concentration;
• code for producing adjustment concentration pattern data, wherein said adjustment concentration pattern data represents a plurality of concentrations within a predetermined concentration range, including the predetermined reference concentration;
• code for printing an adjustment sheet based on the reference pattern data and the adjustment concentration pattern data so that a reference pattern and a plurality of test patterns are printed on the adjustment sheet, wherein the reference pattern indicates the predetermined reference concentration and the test patterns indicate the concentrations indicated by the adjustment concentration pattern data;
• code for comparing a concentration of the reference pattern with the concentrations of the test patterns printed on the adjustment sheet to detect an adjustment concentration value;
• and
• code for adjusting concentration data of image data to be printed in accordance with an adjustment concentration value detected, wherein said reference concentration pattern data and adjustment concentration pattern data are arranged so that a color from the reference pattern and a color of the test pattern is added to the color of the test patterns.