To provide an image processor capable of executing screen processing in order to improve readability while holding more information of input images.

A control part of the image processor executes screen processing for the input image read by an original read part. The control part reads the input image and detects a character region and a background region (S100, S101). The control part calculates edge intensity for pixels in the character region and executes edge determination (S102, S103). When the edge is not determined for a target pixel at the boundary part of the character region and the background region (S104:YES, S105:NO), the control part extends an outer edge region (S107), and replaces image data in the extended region (S108). Thus, the character region and the background region are separated and the readability of output images is improved. When the edge is determined for the target pixel at the boundary part (S105:YES), edge emphasis processing is executed (S106).