Abstract: A method and apparatus for handling transparency operatives simultaneously with raster operatives in a graphics environment. This is achieved by introducing filter operations to obtain the effect of transparency. Filter operations work cooperatively with grayscale and continuous-tone color raster operations. The introduction of filter operations, and their cooperation with raster operations allows this otherwise computationally complex problem to be served by a single hardware circuit for use in real-time applications such as monochrome and color laser printing. The solution is also applicable to displaying complex graphics on a video display device. A suitable apparatus receives graphics language commands which define the image to be displayed and generates a set of graphics orders from the graphics language commands representing the image to be displayed. The apparatus includes an image generator for generating a bitmap image from the graphics orders.

Abstract: A method and apparatus for losslessly compressing binary data using a technique referred to as Double Run-Length Encoding (DRLE). DRLE has particular application to the compression of gray-scale data as it is being processed for printing by a laser printer or other continuous raster scan device. DRLE records repeating patterns of ones and zeros with little computational complexity. Compression ratios that may be an order of magnitude or more are obtained frequently on data that may not compress well using traditional Run-Length Encoding (RLE). DRLE uses a sequential history of order-pairs that denote variable-length patterns of zeros and ones, and then encodes these patterns as they repeat themselves.