System for rotating binary images

Abstract

A method and apparatus for converting an image in run representation form into a raster image which is rotated by some multiple of 90.degree. from the orientation of the original image is disclosed wherein the original image data which is stored in run end or run length form may be divided and stored in discontiguous blocks. In implementing a 90.degree. rotation, the image data is conceptually divided into vertical strips, each of which is independently rotated to create a horizontal strip of the output image. The rotation process is carried out by firstly converting the run representation image data to raster form, dividing the data in each row among a number of intermediate buffers, each of which contains the data from one vertical strip of the original image. The contents of each buffer are rotated and rearranged in an available buffer to form a horizontal strip of the rotated image ready for raster readout. Similarly, a convenient method of rotating the input image 180.degree. is also described wherein the original image is read in run representation form a row at a time and the rows are converted to raster form and placed in storage in reverse order, with the order of the bits in each row also reversed.