A method and apparatus are provided for the processing of an image, such as a document. The invention determines the location of differing content types within the document allowing specialized processing of various content types. The invention performs the identification of pixels having similar content characteristics into windows during the first scanning pass of the document by the use of an identifier equivalence table to update selected memory locations to a base identifier during processing. A second pass processing is available to enhance or alter the image by the use of the information gathered during first pass processing. The present invention benefits from a very low memory requirement while being able to determine windows extending the length or width of the image.