Image processing apparatus and method for correcting image distortion using correction value

An image processing method comprising:

• forming, on a sheet, a pattern from which at least a first line and a second line each connecting two points located at positions parallel to a conveyance direction of the sheet are detectable;
• detecting, from the formed pattern, lengths of the first and second lines each connecting two points located at positions parallel to the conveyance direction;
• acquiring a correction value used when correction is performed so that there is no difference between the lengths of the first and second lines, and
• forming an image obtained by correcting a corrected image to be output using the acquired correction value,
• wherein the second line is shorter than the first line, the correction value acquired includes a magnification ratio in a sub-scanning direction to increase the length of the second line, and the magnification ratio differs depending on a position in the sheet with respect to a main-scanning direction of the sheet.

A non-transitory computer-readable storage medium storing a program, that when executed causes a computer to execute image processing comprising:

• forming, on a sheet, a pattern from which at least a first line and a second line each connecting two points located at positions parallel to a conveyance direction of the sheet are detectable;
• detecting, from the formed pattern, lengths of the first and second lines each connecting two points located at positions parallel to the conveyance direction;
• acquiring a correction value used when correction is performed so that there is no difference between the lengths of the first and second lines, and
• forming an image obtained by correcting a corrected image to be output using the acquired correction value,
• wherein the second line is shorter than the first line, the acquired correction value includes a magnification ratio in a sub-scanning direction to increase the length of the second line, and the magnification ratio differs depending on a position in the sheet with respect to a main-scanning direction of the sheet.