Image forming apparatus and image forming method that can print concealable characters in a particular color

An image forming apparatus comprising:

• a sheet reading portion configured to read, by referring to a plurality of color patches of different colors previously stored in a predetermined memory, image data from a transparent sheet tinted with a predetermined color owned by a user;
• an assimilation surveying portion configured to look for, out of printable colors, a particular color that assimilates to a color of the image data read from the transparent sheet and to identify a color similar to a color of the transparent sheet from the plurality of color patches;
• a color changing portion including a document input screen which accepts data of a predetermined document from the user, the color changing portion being configured to change, out of data of a predetermined document accepted from the user via the document input screen, a color of data of a concealable character, which is a character concealed when overlaid with the transparent sheet, to the found particular color;
• and
• a printing portion configured to print, out of the data of the document, the data of the concealable character a color which is in changed the particular color and which assimilates to the color of the transparent sheet,
• wherein
• the sheet reading portion is configured to
• print a chart with color patches of different colors within a range of printable colors, and
• display an image reading screen inviting the user to perform image reading with the transparent sheet laid over a chart with color patches of colors close to the color of the transparent sheet, in order to read image data of the transparent sheet in a state laid over the color patches on the chart, and
• the assimilation surveying portion is configured to judge whether or not, out of the read image data, the color of the transparent sheet is similar to a color of a color patch overlaid with the transparent sheet;
• wherein the sheet reading portion is configured to identify, out of the read image data, an outline of the transparent sheet, and when the particular color is not found inside the identified outline of the transparent sheet,
• displays the image reading screen once again to invite the user to perform image reading with the transparent sheet moved to over a chart with color patches of colors different from the colors of the color patches over which the transparent sheet is currently laid, in order to read image data of the transparent sheet in a state laid over the color patches of the different colors.