A liquid discharge system comprising: a pretreatment execution device configured to perform pretreatment on a medium; a liquid discharge head configured to discharge liquid onto the medium based on image information on an image to be output; and a pretreatment execution controller configured to control a manner of the pretreatment based on the image information, wherein the pretreatment execution device includes a first pretreatment discharge head to discharge droplets of a first pretreatment agent comprising an aggregating agent having the property of changing a dispersion state of pigment particles applied onto the medium, wherein said pigment particles are contained in coloring liquid droplets discharged from the liquid discharge head, and a second pretreatment discharge head to discharge droplets of a second pretreatment agent comprising said aggregating agent, wherein the concentration of the aggregating agent in the second pretreatment agent is lower than the concentration of the aggregating agent of the first pretreatment agent discharged from the first pretreatment discharge head, wherein the pretreatment execution device is configured to apply the first and second pretreatment agent to the medium, wherein a dot size and a distribution concentration of the pigment particles in a dot are controlled by controlling an amount of the first pretreatment agent and the second pretreatment agent applied to each pixel, depending on a pretreatment region on the medium, characterized in that the dot size and the distribution concentration of the pigment particles are varied by variation of the amount of the first pretreatment agent and the second pretreatment agent associated to a given coloring liquid droplet size. a pretreatment execution device configured to perform pretreatment on a medium; a liquid discharge head configured to discharge liquid onto the medium based on image information on an image to be output; and a pretreatment execution controller configured to control a manner of the pretreatment based on the image information, wherein the pretreatment execution device includes a first pretreatment discharge head to discharge droplets of a first pretreatment agent comprising an aggregating agent having the property of changing a dispersion state of pigment particles applied onto the medium, wherein said pigment particles are contained in coloring liquid droplets discharged from the liquid discharge head, and a second pretreatment discharge head to discharge droplets of a second pretreatment agent comprising said aggregating agent, wherein the concentration of the aggregating agent in the second pretreatment agent is lower than the concentration of the aggregating agent of the first pretreatment agent discharged from the first pretreatment discharge head, wherein the pretreatment execution device is configured to apply the first and second pretreatment agent to the medium, wherein a dot size and a distribution concentration of the pigment particles in a dot are controlled by controlling an amount of the first pretreatment agent and the second pretreatment agent applied to each pixel, depending on a pretreatment region on the medium, characterized in that the dot size and the distribution concentration of the pigment particles are varied by variation of the amount of the first pretreatment agent and the second pretreatment agent associated to a given coloring liquid droplet size.