Ink-jet printing head and ink-jet printing apparatus

An ink-jet printing system for performing printing on a printing medium by ejecting ink, comprising:

• a printing portion having ejection openings for ejecting the ink, an ink mixing chamber for mixing the ink to be ejected, and a plurality of ink chambers respectively storing inks having mutually different ink densities for supplying the inks to said ink mixing chamber;
• a target density setting portion for setting an ink density having relatively high use frequency as a target ink density on the basis of image data inputted from outside of said system for printing an image;
• a mixture ratio calculating portion for calculating, on the basis of target ink density data set by said target density setting portion, a first mixture ratio of an amount of a residual ink in said ink mixing chamber of said printing portion to an amount of a first ink to be supplied to said ink mixing chamber so that the ink density in said ink mixing chamber of said printing portion becomes the target ink density, wherein said mixture ratio calculating portion calculates a second mixture ratio of amounts of the inks to be supplied to said ink mixing chamber from said plurality of ink chambers so that the ink density in said ink mixing chamber can be maintained at the target ink density during printing;
• a discharge operation control portion for causing ink discharge means to perform a discharge operation before printing for discharging a predetermined amount of the residual ink in said ink mixing chamber on the basis of the first mixture ratio calculated by said mixture ratio calculating portion;
• a supply operation control portion for causing ink supply means to perform a first ink supply operation before printing for supplying a predetermined amount of the first ink to said ink mixing chamber on the basis of the first mixture ratio calculated by said mixture ratio calculating portion, wherein said supply operation control portion causes said ink supply means to perform a second ink supply operation during printing for supplying amounts of the inks stored in said plurality of ink chambers to said ink mixing chamber on the basis of the second mixture ratio calculated by said mixture ratio calculating portion;
• and
• a printing operation control portion for causing said printing portion to perform a printing operation on the basis of the image data.