Image scanning apparatus for scanning both sides of an original sheet with a simple memory structure and an image data outputting apparatus for separating image data of each side from image data of both sides

摘要

An image scanning apparatus efficiently compresses and encodes image data obtained by scanning both sides of an original sheet by using a line memory storing three lines. Image data output from a first scanner and image data output from a second scanner are alternately output from a switching unit on an individual line basis. The line memory stores three consecutive lines of the image data output from the switching unit. The three lines include a current line, an immediately preceding line and a second immediately preceding line immediately preceding the immediately preceding line, the current line including a current pixel being encoded. Reference pixels are extracted from among pixels included in the current line and the second immediately preceding line. A pixel value of the current pixel is encoded by using a predicted pixel value of the current pixel as a parameter so as to output encoded image data corresponding to both sides of the original sheet. The prediction of the pixel value is performed by referring to the reference pixels.