An image forming apparatus, comprising: a dot image forming unit configured to selectively execute one of: (i) a default mode of forming, if printable data described in a specific page description language includes a rectangle drawing instruction, a dot image of an entire rectangle by placing an internal dot group corresponding to a fill of an inside portion of a rectangle in a coordinate space based on a first dot placement rule and placing a contour dot group corresponding to a contour of the rectangle in the coordinate space based on a second dot placement rule; or (ii) a change mode of forming the dot image of the entire rectangle by unifying dot placement rules into either the first dot placement rule or the second dot placement rule and placing the internal dot group and the contour dot group in the coordinate space; and an image formation control unit configured to cause, while the change mode is selected, the dot image forming unit to unify the dot placement rules into either the first dot placement rule or the second dot placement rule and to place the internal dot group and the contour dot group in the coordinate space, characterized in that the image formation control unit is configured to determine whether a line-shaped blank occurs in the inside portion of the rectangle when the dot image of the entire rectangle is formed in the default mode, and the image formation control unit is further configured to select the change mode if it is determined that the line-shaped blank occurs. a dot image forming unit configured to selectively execute one of: (i) a default mode of forming, if printable data described in a specific page description language includes a rectangle drawing instruction, a dot image of an entire rectangle by placing an internal dot group corresponding to a fill of an inside portion of a rectangle in a coordinate space based on a first dot placement rule and placing a contour dot group corresponding to a contour of the rectangle in the coordinate space based on a second dot placement rule; or (ii) a change mode of forming the dot image of the entire rectangle by unifying dot placement rules into either the first dot placement rule or the second dot placement rule and placing the internal dot group and the contour dot group in the coordinate space; and (i) a default mode of forming, if printable data described in a specific page description language includes a rectangle drawing instruction, a dot image of an entire rectangle by placing an internal dot group corresponding to a fill of an inside portion of a rectangle in a coordinate space based on a first dot placement rule and placing a contour dot group corresponding to a contour of the rectangle in the coordinate space based on a second dot placement rule; or (ii) a change mode of forming the dot image of the entire rectangle by unifying dot placement rules into either the first dot placement rule or the second dot placement rule and placing the internal dot group and the contour dot group in the coordinate space; and an image formation control unit configured to cause, while the change mode is selected, the dot image forming unit to unify the dot placement rules into either the first dot placement rule or the second dot placement rule and to place the internal dot group and the contour dot group in the coordinate space, characterized in that the image formation control unit is configured to determine whether a line-shaped blank occurs in the inside portion of the rectangle when the dot image of the entire rectangle is formed in the default mode, and the image formation control unit is further configured to select the change mode if it is determined that the line-shaped blank occurs.