1. A method of generating ink amount data which is the used amounts of inks of respective colors when an image is printed, by analyzing image data of the image, the method comprising: extracting a character area, having a predetermined color, from the image by analyzing the image data; dividing the character area into a character contour area which is a contour part of the character and a character inside area which is the inside of the character; converting the image data of the character contour area and the image data of the character inside area into the ink amount data of at least one type of achromatic color ink and at least three types of chromatic color inks; setting a plurality of lattice points in an RGB color solid defined by gray level ranges of RGB components of RGB image data and storing a first correspondence table in which the lattice points correspond to the ink amount data of the at least one type of achromatic color ink and the at least three types of chromatic color inks; storing a second correspondence table in which a plurality of brightness values which is previously selected corresponds to the ink amounts data of the at least three types of chromatic color inks, which results in the predetermined color by concurrent use thereof; storing a predetermined correspondence relationship in which edge lattice points which are the lattice points in a predetermined area including an edge line in which two of the RGB components become an upper limit or a lower limit corresponds to the brightness values of the second correspondence table in the RGB color solid; generating a synthetic correspondence table in which the second correspondence table is embedded in the edge lattice points of the first correspondence table by enabling the brightness values of the second correspondence table to correspond to the edge lattice points according to the correspondence relationship; and generating corrected image data, in which the character inside area is corrected, by converting the RGB components of the image data into the RGB components of the edge lattice points which correspond to the brightness values obtained from the image data by the correspondence relationship, with respect to the image data of the character inside area, wherein the converting of the ink amount data includes converting the image data of the areas into the ink amount data such that the chromatic color inks are largely used in the character inside area compared with the character contour area; the converting of the ink amount data includes converting the image data into the ink amount data by obtaining the brightness value from the image data and referring to the second correspondence table with respect to the image data of the character inside area, and by obtaining RGB components from the image data and referring to the first correspondence table with respect to the image data of the character contour area; and the converting of the ink amount data includes converting the corrected image data into the ink amount data by referring to the synthetic correspondence table.