1. An image processor for restoring bi-level pixel data having black and white levels to multi-level pixel data comprising: a first calculation means for counting a number of pixels in a window having a black level including a specified pixel to be decoded and other pixels to get a smoothing component; second calculation means, having two sets of window pairs, for detecting an edge amount from a difference in the number of pixels having a black level between the windows, wherein one of the window sets has a pair of windows with a width of one pixel and another of the window sets has a pair of windows wider than said one window set; and restoring means for restoring the data for the specified pixel from bi-level to multi-level according to the smoothing component obtained by said fist calculation means and the edge component obtained by said second calculation means; wherein said second calculation means has two groups of two sets of window pairs for detecting an edge component in a same direction but of opposite sides and has a window pair of a width of one pixel in the edge direction, and said second calculation means detects an edge component obtained by the windows of width of one pixel from the sum of edge components of the same direction but of opposite sides.