Abstract: This is a halftone circuit which, in addition to the usual counting and addressing mechanisms, has control over the phase, angle and direction of the addressing circuitry of the array in memory so that regular dots, mirror images of dots and out-of-phase dots can be created from a single array, thus saving memory hardware. The mirror images can be made by counting rows in either direction, the angle can be varied by varying the number of pixels shifted between scans, and the phase can be varied by setting the starting point to any row and column. In this way, a single array can be used to create a number of dots.

Abstract: An object optimized printing system and method comprises a page description language decomposing system, a command instruction and data generating system and an image output terminal controller. The PDL decomposition system inputs a print file defining a plurality of pages in the page description language and locates the plurality of objects forming each page and their object types. Based on the determine object types and any explicit rendering commands in the PDL file, the PDL decomposition system automatically generates rendering tags for each of the objects. The rendering tags are used to control the command instruction and data generating system, the IOT controller and/or the image output terminal to optimize the printing by the IOT on an object-by-object basis. Based on the objects and the generated rendering tags, the command instruction and data generating system generates the differing types of data and the command instructions on a scanline-by-scanline basis.

Abstract: A circuit which uses less memory to store halftone arrays in a high addressability printer by storing regular halftone arrays as low addressability arrays and by outputting each pixel a number of times, the number being the ratio of high to low addressability. For example, if a high addressability system uses 4 sub pixels for each pixel, then one value of each low addressability array is stored in one location and the halftone circuit is controlled to output that value 4 times, once for each sub pixel thus saving memory by a factor of 4.

Abstract: A method and apparatus are provided for improving the quality of a printed image by first automatically determining the gamma (&ggr;) of an image, and then adjusting the &ggr; of the printer, if necessary, to correspond to that of the image. Thus, if an image has a &ggr; of 2, the &ggr; of the printer will be adjusted from approximately 1 (its normal &ggr;), to approximately 2 (i.e., corresponding to that of the image). To detect the &ggr; difference problem, the invention detects a shift in saturated colors towards higher digital counts. Then, through mapping of the color space from three dimensions to two dimensions and cross-plotting values of saturation and luminance, a cumulative histogram plot of luminance is developed. The histogram displays the 256 luminance bands, arranged in one of eight bands, and normalized from zero to one. A threshold value is established for the cumulative histogram plot and the value of the cumulative histogram is compared to the threshold.

Abstract: An object optimized printing system and method comprises a page description language decomposing system, a command instruction and data generating system and an image output terminal controller. The PDL decomposition system inputs a print file defining a plurality of pages in the page description language and locates the plurality of objects forming each page and their object types. Based on the determine object types and any explicit rendering commands in the PDL file, the PDL decomposition system automatically generates rendering tags for each of the objects. The rendering tags are used to control the command instruction and data generating system, the IOT controller and/or the image output terminal to optimize the printing by the IOT on an object-by-object basis. Based on the objects and the generated rendering tags, the command instruction and data generating system generates the differing types of data and the command instructions on a scanline-by-scanline basis.

Abstract: A scanner generates a first set of M-bit signals representing an image in a document. A default table translates the M-bit signals into linearized N-bit signals where M>N. A color image processing module processes the N-bit signals to generate an image-dependent look-up table which, thereafter, is loaded into the scanner. The scanner then generates a second set of M-bit signals using a high resolution re-scan of the same image. The second set of M-bit signals are translated into N-bit signals using the image-dependent look-up table to generate an electronic representation with enhancement characteristics.

Abstract: A technique for calibrating the hardware and software of a digital printing apparatus relies on making seven component test patches which completely characterize the printing system, and then measuring the actual reflectance of these seven test patches. The measured reflectances are then converted, by the Yule-Nielsen equation, to values representative of the ink area coverage characteristic of each component test patch, because ink area coverage is the parameter that can be directly controlled by the digital printer. This conversion step takes into account the non-linear relationship between the reflectance of a halftone area and the amount of ink area coverage on the halftone area.

Abstract: A halftone generator for generating tint dots that are more circular than typical Holladay dots. Two threshold arrays are used, one that is pixel-centered and one that is interstice-centered. For each signal input level, the one that will produce a more circular dot will be selected by a look-up table driven by the image signal input. A single array version can also be used. The stored array has pixel-centered thresholds at one end and interstice-centered thresholds at the other. The circuit can either choose an array output or an inverted array output to generate either pixel-centered or interstice-centered light and dark coverage.

Abstract: An object optimized printed system includes an image output terminal controller. The system inputs a print file defining a plurality of pages in a page description language and locates the plurality of objects forming each page and their object types. Based on the determine object types and any explicit rendering commands in the PDL file, the system automatically generates rendering tags for each of the objects. The rendering tags are used to control the image output terminal to optimize the printing by the IOT on an object-by-object basis. Based on the objects and the generated rendering tags, the system generates the differing types of data and the command instructions on a scanline-by-scanline basis. The generated command instructions and data are output to the IOT controller scanline-by-scanline. The data output to the IOT controller includes metabit data which is generated from the rendering tags.

Abstract: A calibration system, for calibrating a printer response to halftone images directed thereto, includes a test pattern, stored in a memory, providing a plurality of samples of combinations of printed spots, printable on a media by the printer; a gray measuring device, to derive a gray measurement of the samples of printed spots; a calibration processor correlating gray measurements with a particular combination of spots, and deriving parameters describing the printer response to the particular combination; generating at least one gray image correction, including a set of correction values selected in accordance with said the described printer response, and a calibration memory, storing the generated halftone patterns.

Abstract: A method of halftone printing in four colors using, for cyan, magenta and black, halftone screens that will result in screening angles of 15, 45 and 75 degrees, as is the standard process in the art, and a halftone screen for yellow that will result in screening angles of 0, +60 and -60 degrees. This combination will diminish the 2 color moire patterns that result from the interaction between the yellow and one of the other colorants. The 0 and + or -60 degree screening angles are generated by using a screen that produces a four-centered cell having dots that are spaced to form hexagons, when the nearest neighbors of a central dot are connected by lines, as opposed to the conventional trapezoidal orientation.

Abstract: A method of quantizing pixel values in an image formed by a plurality of pixels, each pixel representing an optical density of the image at a location within the image, and having an original optical density value selected from one of a set of `c` original optical density values that has a number of members larger than a desired output set of `d` optical density values through a process of combined halftoning and cell-to-cell error diffusion. Initially, each pixel is modified with a pro rata portion of an error term determined for a previous halftone cell, or from the current cell in a previous interaction. A set of modified pixels, corresponding in position to an m.times.n halftone cell, are processed in accordance with a standard halftoning process, to derive a set of output pixels at one of d optical density levels.

Abstract: A set of halftone screens and a write white xerographic system for generating halftone images with a minumum of artifacts. The screens used in a four color printer have at least 64 pixels per pattern and are distributed to creat fourcentered dots that are at either -14, 0,+14 or +45 degrees. The xerographic process involves charging the photoreceptor, partially discharging the photoreceptor with a scanning beam to create an image, and then using toner which adheres to the charged portions of the photoreceptor to create the hard copy.

Abstract: Encoding and decoding between fixed and variable length binary codes to achieve data compression and decompression is performed without the necessity for storing the entire variable length minimum redundancy code format. In encoding, data is compressed by generating a minimum redundancy code of a bit length and binary value inversely proportional to the probability of an occurrence of the fixed length binary message from which the minimum redundancy binary code symbol is derived. The compressed binary symbols are transmitted or stored in serial form. In decoding, data is decompressed by sequentially generating portions of threshold binary symbols in the minimum redundancy code and comparing with corresponding portions of a received or recovered binary symbol as it is shifted through the decoder. The comparison results define the bit length and binary value of the binary symbol without the necessity for ever storing the binary symbol in its entirety.