Inkjet printing apparatus and control method therefor

An inkjet printing apparatus comprising:

• a printhead adopting an inkjet printing method;
• a reading unit configured to read an image;
• a first creation unit configured to create first shading data using data of an image obtained by reading a white reference by the reading unit;
• a first obtaining unit configured to obtain data of an image of a background of a print medium by reading the print medium by the reading unit;
• a second obtaining unit configured to obtain data of an image formed by a predetermined ink among a plurality of inks by reading, by the reading unit, a test pattern formed using the plurality of inks on the print medium by the printhead;
• a second creation unit configured to create second shading data using the data of the image of the background and the data of the image formed by the predetermined ink;
• a correction unit configured to correct, with respect to the data of the image of the test pattern read by the reading unit, a signal value corresponding to a first color using the first shading data and a signal value corresponding to a second color using the second shading data so that data of a value lower than a value of the second shading data becomes a value corresponding to a lowest luminance;
• a specifying unit configured to specify, using the signal value corrected by the correction unit, an area of a pattern formed by each of the plurality of inks in the image of the test pattern;
• and
• a calculation unit configured to calculate a printing position deviation amount on the print medium between the plurality of inks based on a position of the pattern of the area specified by the specifying unit.

A control method for an inkjet printing apparatus including a printhead adopting an inkjet printing method and a reading unit, comprising:

• creating first shading data using data of an image obtained by reading a white reference by the reading unit;
• obtaining data of a first image by reading, by the reading unit, a test pattern formed using a plurality of inks on a print medium by the printhead and correcting signal values of pixels in an image of the test pattern using the first shading data;
• obtaining data of an image of a background of the print medium by reading the print medium by the reading unit;
• obtaining data of an image formed by a predetermined ink among the plurality of inks by reading the test pattern by the reading unit;
• creating, using the data of the image of the background and the data of the image formed by the predetermined ink, second shading data having a value between a value of the data of the image of the background and a value of the data of the image formed by the predetermined ink;
• obtaining data of a second image by correcting, using the second shading data, the signal values of pixels in the image of the test pattern read by the reading unit so that the signal value of a pixel lower than a value of the second shading data becomes a value corresponding to a lowest luminance;
• specifying an area of a pattern of each of the plurality of inks in the image of the test pattern using the data of the first image and the data of the second image;
• and
• calculating a position deviation amount of the printhead based on a position of the pattern of the specified area.