Inkjet printing apparatus and variable-density correction method

An inkjet printing apparatus for printing an image on a surface of a recording medium, comprising:

• a head having a plurality of nozzles arranged in a main scanning direction, said plurality of nozzles ejecting ink to a surface of a recording medium;
• a transport mechanism that transports a recording medium relative to said head in a sub-scanning direction orthogonal to said main scanning direction;
• an image capturing part that captures an image of a surface of a recording medium at an image capturing position located downstream of said head in said sub-scanning direction;
• a detector that detects an amount of displacement in position of a recording medium in said main scanning direction at said image capturing position;
• and
• a controller connected to said head, said transport mechanism, said image capturing part, and said detector,
• said controller including:
• a chart print instruction part that controls and causes said head and said transport mechanism to print a shading chart whose density changes in a stepwise fashion in said sub-scanning direction on a recording medium;
• an image acquisition part that controls and causes said image capturing part to acquire a plurality of captured images for a region of the same density of said shading chart;
• an ultra-resolution processing part that generates one super-resolution image with a higher resolution than said plurality of captured images on the basis of said plurality of captured images acquired by said image capturing part, and amounts of displacement in position of a recording medium in said main scanning direction acquired by said detector;
• and
• a correction amount calculation part that calculates a variable-density correction amount for each of said plurality of nozzles on the basis of said ultra-resolution image.