An image forming apparatus includes a reading unit for sequentially reading, from image data, pieces of pixel data of target pixels along a predetermined direction, a cumulative sum calculation unit for calculating a cumulative sum of gradation values represented by pieces of pixel data of target pixels in a significant image portion read by the reading unit, a determination unit for determining whether the target pixel read by the reading unit is located at a boundary between the significant image portion and a background portion that is a non-significant image portion, and a correction unit for correcting, if the determination unit determines that the target pixel is located at the boundary, a gradation value represented by pixel data of the target pixel by adding a correction amount based on the cumulative sum up to the target pixel calculated by the cumulative sum calculation unit to the gradation value.

An image processing apparatus includes an output image reading portion that reads an image of a physical document. The physical document includes a desired print image and a line image. The apparatus further includes a line image detecting portion that detects the line image at a predetermined position of the physical document using the image, a line image analyzing portion that determines a line width of the line image, a line-width correction value determining portion that compares the determined line width to a preliminarily set line-width threshold value and determines a line-width correction value based on the comparison, and a line-width correcting portion that performs line width correction on a to be formed line image based on the line-width correction value.

An image forming system includes a computer and an image forming apparatus. The computer includes a print data generating circuit to generate print data of an image. The image forming apparatus includes a rendering circuit to execute rendering of the image based on the print data. The computer includes an image generating circuit generates an image object to indicate a state where the objects are overlapped in the image with a reduced resolution at least partially. The print data generating circuit generates the print data including the at least one object included in the image and the image object generated by the image generating circuit. When the rendering circuit processes the image object, the rendering circuit enhances the resolution of a part corresponding to the object in the image object based on a shape of the object overlapped at upper side in the image object.