Method and apparatus for determining a correction pattern of periodical unevenness of an apparatus in which optical beams are reflected by a rotating polygonal mirror and scan a recording body

A method of forming an image corresponding to an input image signal by a light beam generation means for generating a light beam, a drive means for driving the light beam generation means, and an image outputting means for scanning said light beam which has been reflected by a rotary polygonal mirror to a recording medium in a primary direction and for moving said recording medium in a secondary direction which is substantially perpendicular to said primary direction so that said image is formed, the method comprising the steps of:

• changing a phase or an amplitude of a first reference signal having a fundamental frequency in which one rotation of said polygonal mirror is one period;
• generating a plurality of periodical modulation signals having different phases or different amplitudes from each other;
• generating a plurality of periodical multiplying signals by multiplying a second reference signal having a predetermined value by said plurality of periodical modulation signals, respectively;
• forming images onto said recording medium respectively corresponding to said plurality of periodical multiplying signals by controlling said drive means and said image outputting means corresponding to said plurality of periodical signals;
• selecting a first periodical modulation signal which is one of said plurality of periodical modulation signals corresponding to a first position on said recording medium, and a second periodical modulation signal which is one of said plurality of periodical modulation signals corresponding to a second position on said recording medium which is different from said first position on said recording medium;
• calculating a density unevenness correction signal in response to selected first and second periodical modulation signals;
• controlling said drive means and said image outputting means in response to said input image signal corrected by said density unevenness correction signal;
• and
• forming said image in response to said input image signal corrected by said density unevenness correction signal.

A method of forming an image corresponding to an input image signal by a light beam generation means for generating a light beam, a drive means for driving said light beam generation means, and an image outputting means for scanning said light beam which has been reflected by a rotary polygonal mirror to a recording medium in a primary direction and for moving said recording medium in a secondary direction which is substantially perpendicular to said primary direction so that said image is formed, the method comprising the steps of:

• changing a phase of a first reference signal having a fundamental frequency in which one rotation of said polygonal mirror is one period;
• generating a plurality of first periodical modulation signals having different phases from each other;
• generating a plurality of first periodical multiplying signals by multiplying a second reference signal having a predetermined value by said plurality of first periodical modulation signals, respectively;
• forming images onto said recording medium respectively corresponding to said plurality of first periodical multiplying signals by controlling said drive means and said image outputting means corresponding to said plurality of first periodical multiplying signals;
• selecting at least one of said phases of said first periodical modulation signals;
• changing an amplitude of said first reference signal having said selected at least one of said phases;
• generating a plurality of second periodical modulation signals having different amplitudes from each other;
• generating a plurality of second periodical multiplying signals by multiplying said second reference signal by said plurality of second periodical modulation signals, respectively;
• forming images onto said recording medium respectively corresponding to said plurality of second periodical multiplying signals by controlling said drive means and said image outputting means corresponding to said plurality of second periodical multiplying signals;
• selecting at least one of said amplitudes of said second periodical modulation signals;
• calculating a density unevenness correction signal in response to said selected at least one of said phases and said selected at least one of said amplitudes;
• controlling said drive means and said image outputting means in response to said input image signal corrected by said density unevenness correction signal;
• and
• forming said image in response to said input image signal corrected by said density unevenness correction signal.