1. A display control apparatus comprising: an image memory having a plurality of storage addresses, each of said plurality of storage addresses storing a pattern code indicating a pattern to be displayed and an attribute code indicating modification of a pattern designated by said pattern code stored at the same storage address; an address circuit for serially selecting said storage addresses of said image memory one by one; a control memory for storing a control code assuming one of first and second states which is independent of the contents of attribute codes of said image memory; means for designating a storage address of said image memory to be modified; means responsive to said storage address designated by said designating means for setting said control code to said first state when said storage address selected by said address circuit coincides with said designated designated storage address, and to said second state when said storage address selected by said address circuit does not coincide with said storage address; a control circuit receiving said attribute code, and said control code stored in said control memory, said control circuit generating an attribute execution signal only when said control code is in said first state; and a video signal generator coupled to said image memory and said control circuit for generating a first video signal representing a pattern corresponding to said pattern code without modification thereof when said control code is in said second state, and for generating a second video signal representing a modified pattern which corresponds to said pattern code and is modified by said attribute code when said control code is in said first state, wherein either one of said first and second video signals is generated from the same contents of said image memory according to said control code.