Image processing apparatus, image processing method, and storage medium which reduce a color difference and a frequency difference between two images

An image printing method for a printing apparatus with a printing unit configured to print an image with a plurality of chromatic inks and an achromatic ink, wherein the printing apparatus includes a first nozzle array including a plurality of nozzles for discharging first chromatic ink arranged in a predetermined direction, a second nozzle array including a plurality of nozzles for discharging second chromatic ink arranged in the predetermined direction, a third nozzle array including a plurality of nozzles for discharging third chromatic ink arranged in the predetermined direction, and a fourth nozzle array including a plurality of nozzles for discharging achromatic ink arranged in the predetermined direction, prints an image in a first area on a printing medium with use of a first nozzle group including at least one nozzle in the first nozzle array, a second nozzle group including at least one nozzle in the second nozzle array, a third nozzle group including at least one nozzle in the third nozzle array, and a fourth nozzle group including at least one nozzle in the fourth nozzle array, and prints an image in a second area different in position in the predetermined direction from the first area on the printing medium with use of a fifth nozzle group in the first nozzle array, the fifth nozzle group not including nozzles included in the first nozzle group, a sixth nozzle group in the second nozzle array, the sixth nozzle group not including nozzles included in the second nozzle group, a seventh nozzle group in the third nozzle array, the seventh nozzle group not including nozzles included in the third nozzle group, and an eighth nozzle group in the fourth nozzle array, the eighth nozzle group not including nozzles included in the fourth nozzle group,

• the image printing method comprising:
• converting a first combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink and a color signal corresponding to the achromatic ink, which are input to be printed in the first area, into a second combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink, and a color signal corresponding to the achromatic ink, and
• converting a third combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink, and a color signal corresponding to the achromatic ink, which are input to be printed in the second area, into a fourth combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink, and a color signal corresponding to the achromatic ink,
• printing an image to the first area based on the converted color signal corresponding to the first chromatic ink included in the second combination, the converted color signal corresponding to the second chromatic ink included in the second combination, the converted color signal corresponding to the third chromatic ink included in the second combination and the converted color signal corresponding to the achromatic ink included in the second combination, and
• printing an image to the second area based on the converted color signal corresponding to the first chromatic ink included in the fourth combination, the converted color signal corresponding to the second chromatic ink included in the fourth combination, the converted color signal corresponding to the third chromatic ink included in the fourth combination and the converted color signal corresponding to the achromatic ink included in the fourth combination,
• wherein, in a case where values of the color signals in the first combination equal the respective values of the color signals in the third combination, and
• (1) the value of the color signal corresponding to the achromatic ink is larger than 0,
• (2) at least two of the values of the color signals corresponding to the first, second and third chromatic inks are larger than 0, and
• (3) the value of the color signal corresponding to the achromatic ink is smaller than a sum of the values of the color signals corresponding to the at least two of the first, second and third chromatic inks,
• the converting is performed such that the value of the color signal corresponding to the achromatic ink in the second combination equals the value of the color signal corresponding to the achromatic ink in the first combination, and the value of the color signal corresponding to the achromatic ink in the fourth combination equals the value of the color signal corresponding to the achromatic ink in the third combination,
• so that a difference between a color of the image printed in the first area and a color of the image printed in the second area is reduced and a difference between a frequency of the image printed in the first area and a frequency of the image printed in the second area is reduced.

A non-transitory computer-readable storage medium storing computer-executable instructions that, when executed by a computer, cause the computer to perform an image printing method for a printing apparatus with a printing unit configured to print an image with a plurality of chromatic inks and an achromatic ink, wherein the printing apparatus includes a first nozzle array including a plurality of nozzles for discharging first chromatic ink arranged in a predetermined direction, a second nozzle array including a plurality of nozzles for discharging second chromatic ink arranged in the predetermined direction, a third nozzle array including a plurality of nozzles for discharging third chromatic ink arranged in the predetermined direction, and a fourth nozzle array including a plurality of nozzles for discharging achromatic ink arranged in the predetermined direction, prints an image in a first area on a printing medium with use of a first nozzle group including at least one nozzle in the first nozzle array, a second nozzle group including at least one nozzle in the second nozzle array, a third nozzle group including at least one nozzle in the third nozzle array, and a fourth nozzle group including at least one nozzle in the fourth nozzle array, and prints an image in a second area different in position in the predetermined direction from the first area on the printing medium with use of a fifth nozzle group in the first nozzle array, the fifth nozzle group not including nozzles included in the first nozzle group, a sixth nozzle group in the second nozzle array, the sixth nozzle group not including nozzles included in the second nozzle group, a seventh nozzle group in the third nozzle array, the seventh nozzle group not including nozzles included in the third nozzle group, and an eighth nozzle group in the fourth nozzle array, the eighth nozzle group not including nozzles included in the fourth nozzle group,

• the image printing method comprising:
• converting a first combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink and a color signal corresponding to the achromatic ink, which are input to be printed in the first area, into a second combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink, and a color signal corresponding to the achromatic ink, and
• converting a third combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink, and a color signal corresponding to the achromatic ink, which are input to be printed in the second area, into a fourth combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink, and a color signal corresponding to the achromatic ink,
• printing an image to the first area based on the converted color signal corresponding to the first chromatic ink included in the second combination, the converted color signal corresponding to the second chromatic ink included in the second combination, the converted color signal corresponding to the third chromatic ink included in the second combination and the converted color signal corresponding to the achromatic ink included in the second combination, and
• printing an image to the second area based on the converted color signal corresponding to the first chromatic ink included in the fourth combination, the converted color signal corresponding to the second chromatic ink included in the fourth combination, the converted color signal corresponding to the third chromatic ink included in the fourth combination and the converted color signal corresponding to the achromatic ink included in the fourth combination,
• wherein, in a case where values of the color signals in the first combination equal the respective values of the color signals in the third combination, and
• (1) the value of the color signal corresponding to the achromatic ink is larger than 0,
• (2) at least two of the values of the color signals corresponding to the first, second and third chromatic inks are larger than 0, and
• (3) the value of the color signal corresponding to the achromatic ink is smaller than a sum of the values of the color signals corresponding to the at least two of the first, second and third chromatic inks,
• the converting is performed such that the value of the color signal corresponding to the achromatic ink in the second combination equals the value of the color signal corresponding to the achromatic ink in the first combination, and the value of the color signal corresponding to the achromatic ink in the fourth combination equals the value of the color signal corresponding to the achromatic ink in the third combination,
• so that a difference between a color of the image printed in the first area and a color of the image printed in the second area is reduced and a difference between a frequency of the image printed in the first area and a frequency of the image printed in the second area is reduced.

A system comprising;

• an image printing apparatus, and
• a printing unit configured to print an image with a plurality of chromatic inks and an achromatic ink,
• wherein the printing unit includes a first nozzle array including a plurality of nozzles for discharging first chromatic ink arranged in a predetermined direction, a second nozzle array including a plurality of nozzles for discharging second chromatic ink arranged in the predetermined direction, a third nozzle array including a plurality of nozzles for discharging third chromatic ink arranged in the predetermined direction, and a fourth nozzle array including a plurality of nozzles for discharging achromatic ink arranged in the predetermined direction,
• wherein the printing unit prints an image in a first area on a printing medium with use of a first nozzle group in the first nozzle array, a second nozzle group in the second nozzle array, a third nozzle group in the third nozzle array, and a fourth nozzle group in the fourth nozzle array, and
• wherein the printing unit prints an image in a second area different in position in the predetermined direction from the first area on the printing medium with use of a fifth nozzle group in the first nozzle array, the fifth nozzle group not including nozzles included in the first nozzle group, a sixth nozzle group in the second nozzle array, the sixth nozzle group not including nozzles included in the second nozzle group, a seventh nozzle group in the third nozzle array, the seventh nozzle group not including nozzles included in the third nozzle group, and an eighth nozzle group in the fourth nozzle array, the eight nozzle group not including nozzles included in the fourth nozzle group;
• a multi-color shading (MCS) processing unit configured
• to convert a first combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink and a color signal corresponding to the achromatic ink, which are input to be printed in the first area, into a second combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink, and a color signal corresponding to the achromatic ink, and
• to convert a third combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink and a color signal corresponding to the achromatic ink, which are input to be printed in the second area, into a fourth combination including a color signal corresponding to the first chromatic ink, a color signal corresponding to the second chromatic ink, a color signal corresponding to the third chromatic ink, and a color signal corresponding to the achromatic ink;
• and
• a controller configured
• to control the printing unit,
• to print an image to the first area based the converted color signal corresponding to the first chromatic ink included in the second combination, the converted color signal corresponding to the second chromatic ink included in the second combination, the converted color signal corresponding to the third chromatic ink included in the second combination, and the converted color signal corresponding to the achromatic ink included in the second combination and
• to print an image to the second area based on the converted color signal corresponding to the first chromatic ink included in the fourth combination, the converted color signal corresponding to the second chromatic ink included in the fourth combination, the converted color signal corresponding to the third chromatic ink included in the fourth combination and the converted color signal corresponding to the achromatic ink included in the fourth combination,
• wherein, in a case where values of the color signals in the first combination equal the respective values of the color signals in the third combination, and
• (1) the value of the color signal corresponding to the achromatic ink is larger than 0,
• (2) at least two of the values of the color signals corresponding to the first, second and third chromatic inks are larger than 0, and
• (3) the value of the color signal corresponding to the achromatic ink is smaller than a sum of the values of the color signals corresponding to the at least two of the first, second and third chromatic inks,
• the conversion of the MCS processing unit is performed such that the value of the color signal corresponding to the achromatic ink in the second combination equals the value of the color signal corresponding to the achromatic ink in the first combination, and the value of the color signal corresponding to the achromatic ink in the fourth combination equals the value of the color signal corresponding to the achromatic ink in the third combination,
• so that a difference between a color of the image printed in the first area and a color of the image printed in the second area is reduced and a difference between a frequency of the image printed in the first area and a frequency of the image printed in the second area is reduced.

An image processing apparatus for a printing apparatus,

• wherein the printing apparatus includes
• a plurality of nozzle arrays including a plurality of nozzles arranged in a predetermined direction, each array corresponding to an ink of a plurality of inks, and
• prints an image on a recording medium by discharging the plurality of inks from the plurality of nozzles included in the corresponding nozzle array according to a combination of output color signals determined by the image processing apparatus,
• the image processing apparatus comprising:
• a processor;
• and
• a memory coupled to the processor storing instructions that, when executed by the processor, cause the processor to
• convert input color signals, for printing a first image in a first area of the recording material, into output color signals, for controlling a discharge of ink from the respective nozzles corresponding to the first area,
• convert input color signals, for printing a second image in a second area of the recording material, into output color signals, for controlling a discharge of ink from the respective nozzles corresponding to the second area,
• correct, using Multi-Color Shading (MCS) processing and Head-Shading (HS) processing, the output color signals for predetermined variations in the discharge of the nozzles used in the printing of the first image and the second image, and
• in a case of one ink of the plurality of inks being an achromatic ink, constrain the correction by the MCS processing of the output color signals for the one ink.