An apparatus that corrects multivalued data after halftone processing and which includes a line input unit configured to input multivalued data of a correction line to be corrected among the multivalued data, a detection unit configured to convert multivalued data of a precedent line that precedes the correction line by N lines into dot data and to detect a dot in the precedent line, and a line correction unit configured to correct the multivalued data of the correction line based on a number of linked dots from the bottom-end edge, and the number of linked detected dots is the number of dots that are linked in a sub scanning direction from the correction line down to the bottom-end edge, and the bottom-end edge is an edge at which the density becomes lower in the sub scanning direction and the lower of density values represents the background color.