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: A circuit which can be used to hold either the maximum or minimum voltage applied. A comparator compares the input voltage to the previous high or low and a set of two mirror circuits either charge or discharge a holding copacitor to the new value. A control circuit of transistor switches configures the circuit into either a maximum or minimum holding mode.

Abstract: A look ahead circuit for enabling the calibration of a ROS laser to be calibrated during the active part of the scan. A register takes a number of pixels from the stream of video and compares them to a plurality of possible matching pixel patterns. If a match is found, the pixel pattern is applied to a table look up to produce a digital representation of the laser power that should be produced as a result of these pixels, and this representation is converted in a digital to analog converter to an analog voltage which corresponds to the laser power that the laser should be putting out when generating this set of pixels. During the time when these pixels are being printed, a detector measures the laser power and that is compared to the analog voltage to produce a difference. At the same time, a capture circuit, as the result of finding the match, turns on a sample and hold circuit which couples out the difference as the error output, which is used to correct the laser output.

Abstract: A circuit for using a flying spot scanner of one scan density to produce rasters of a different density in the process direction by using a fractional number of scans per raster. In the usual case, where m scans will be used to create n rasters, the number of scans m will normally be greater than the number of rasters n. Then, there will be m/n scans per raster. This will necessitate dividing some scans into two parts, the first part of the scan being used to scan the video data of the previous raster and the second part of the scan being used to scan the data of the next raster. Therefore, a circuit for switching data to each scan from one line of data to the next as the scan transitions from one raster to the next is required in this system. A process direction encoder can be used to determine when the raster boundaries are reached, and therefore when the data is to be switched.

Abstract: A circuit for reducing the amount of instability in a pulse width modualtion circuit by providing a minimum amount of overdrive after the crossover point between a ramp and a voltage threshold level, and a constant amount of discharge time between the end on one ramp and the beginning of the next. Also, a feedback loop is privided to increase or decrease the slope to compensate for a decreasing or increasing amount of time between clock pulses, to maintain the duty cycle of the output when the clock frequency varies.

Abstract: A method for vacuum depositing a selenium-arsenic coating on a substrate to form a photoreceptor by evaporating selenium with an arsenic concentration of 0.1 to 0.6 percent by weight and discontinuing the evaporation when the weight of the selenium alloy remaining is 2-10 percent of the original weight.

Abstract: A circuit for increasing the speed of conversion of image pixels from one number of bits to another by processing a plurality of pixels in parallel. The conversion of each pixel typically results in a new value and an error term which is divided up among adjacent pixels. By using a plurality of separate conversion circuits, one for each line, and by processing the xth pixel on one line in parallel with the x-2 pixel on the next line, the plurality of pixels can be processed in parallel. All circuits are identical except that the first circuit must get the error term of the line above it from memory, and the last of the parallel circuits must store in memory the error term for the next plurality of lines.

Abstract: In a raster output scanner, a system for using one original beam and one facet of a rotating polygon to generate a scan line which can be turned on to have three levels of intensity. The original beam is first separated into two beams in a beam splitter. The resultant beams are polarized ninety degrees apart, and directed to the modulator. The beams are a sufficient distance apart so that the A/O modulator can modulate each beam with a minimum of crosstalk. The output beams are then brought together and combined into one beam without optical interference because the beams are polarized ninety degrees apart. The beam can have several levels of intensity and be used to create several levels of gray scale at the output.

Abstract: In a raster output scanner, a system for using one original beam and one facet of a rotating polygon to generate two consecutive scan lines. The original beam is first separated into two beams in a beam splitter. The resultant beams are polarized ninety degrees apart, and directed to the modulator. The beams are a sufficient distance apart so that the A/O modulator can modulate each beam with a minimum of crosstalk. The output beams are then brought together to within one scan line separation by a beam recombiner, which is a reversed beam splitter. The beams can be brought together to this close proximity without optical interference because the beams are plarized ninety degrees apart.

Abstract: A raster output scanner which can be instantly varied between the most common spot densities, such as 240, 300, 400 and 600 spots per inch in the slow scan direction. The scanner produces a plurality of scans per inch, either by scanning with one beam or several simultaneous beams, the number of scans per inch being a common denominator of all of the spot densities. For example, for the above spot densities, 1200 scans per inch would be required. Then each scan is independently modulated so that the correct number of spots per inch are generated. Thus, for example, if 4 consecutive scans are used to create one spot, then the spot density will be 300 spots per inch.

Abstract: In a raster output scanner, a method of switching video from one raster to the next during a scan without the creation of a visible artifact. A position encoder is used to determine the position of each raster on the photoreceptor, a first distance above the transition point and a second distance below the transition point, in the process direction. Above the first point the video will be supplied by the first raster, and below the second point the video will be supplied by the second raster. From the first point to the transition point the duty cycle will vary from 100% of data from the first raster to 50% from each raster. From the transition point to the second point the duty cycle will vary from 50% to 100% supplied by the second raster. In this way, there is a gradual, and invisible, transition from one raster to the next.

Abstract: A circuit for enabling the raster display of text or line art in one constant color against a background of another constant color or against a continuous-tone picture, or the display of a continuous-tone picture through an arbitrary shape. The circuit has four channels, one each for constant colors, continuous-tone images, image masks, and instructions. The constant colors are stored in the first channel in the form of two 8-bit colors, one for the text or line art and one for the background. Any color pair can be read from this memory, divided into two 8-bit colors, and presented at two inputs of a final multiplexer. The second channel stores continuous tone color pictures and presents this information at a third input of the multiplexer. The third channel receives masks or outlines in the form of bitmaps and the fourth channel receives instructions which may be run-length encoded. These two channels combine their data, which is then used to control the multiplexer.

Abstract: A method of representing the text in a document in a way that enables very fast text processing on digital computers. More specifically, each word of text is represented as a number (or token) that refers to an information packet describing the word's characteristics. Operations then process each token, rather than each character, to perform text processing functions. In addition to the compact nature of this representation, the performance of virtually all functions in a WYSIWYG editor are improved. In particular, determining line breaks and displaying text are significantly faster when the text is processed a token at a time rather than a character at a time.

Abstract: A catalog of fonts, each font differing with the others in the bit patterns contained in its characters which when printed yield a different color, all fonts comprising the same number of identical characters, the characters being a predetermined number of shapes that can be assembled together to form an area. To the printer, the catalog appears to be a number of fonts, and can therefore be accessed by a printer that has a typical hardware system for printing text. However, when printed using a two-color printer, the printed output will be an area of any size filled in with the specified color.

Abstract: A programming language optimized for the specification of inks for a printing system using two colorants, black plus a highlight color. The first group of statements name the primary colors such as black and red or magenta. Next specified are the catalog name and the palettes which make up the catalog. A palette is a collection of inks, each ink being defined as a tile composed of two bit maps which together are referred to as a screen, each bit map identifying the pixels in the tile to be printed in the associated primary color. Each bit pattern line is specified in the language by an equivalent binary number.

Abstract: A circuit for producing an exact duty cycle for a system having a variable system clock frequency. In the calibrate phase, a waveshape with an exact duty cycle is made by ANDing two or more clock pulse trains, each of which is a multiple of the system clock frequency. This is compared against the output of a current-controlled pulse width modulator which is programmed to produce the same duty cycle. The polarity of the comparator output as a result of the error between the exact duty cycle and the one produced by the modulator increments or decrements a counter, the output of which controls a DAC, which in turn corrects the output of the modulator. After a suitable number of interations, the modulator, which is now calibrated, will reproduce the exact duty cycle. The circuit is then put into the operate mode by disabling the counter, and programming the pulse width modulator to output the desired system duty cycle.

Abstract: A software package is described which resides in a color printing system and which automatically intercepts and colorizes black and white documents (or re-colors color documents, if desired) that are sent to the color printer. The description includes pictorial flow charts and segments of code from an existing implementation in a Pascal-like language, implemented for documents expressed in a high-level page description language (PDL). The functionality of each major process in the software is explained in detail, including as examples the process of capturing and parsing user-specified modifications to the automatic coloring instructions, the process of coloring graphical objects according to their existing fill patterns, the process of coloring text and adding textual features such as dropshadows, and the process of coloring bitmaps.

Abstract: An algorithm for rotating an image 90 degrees starts with an array or r rows and c columns of pixels. Each column of the pixel array is partitioned into words of w pixels each, and the rows, the columns, the words in each column, and the pixels in each word of the pixel array are all numbered starting at zero. Let v= r/w , where r/w is the smallest integer greater than or equal to r/w. Similarly, let h- c/w . The algorithm stores words of the original pixel array into a linear word organized memory as follows: it circular right-shifts each word i of column j by (j)mod w pixel positions and then writes in parallel this modified word into word address vj+i of the memory.

Abstract: A system for using the page buffer memory which stores the pixel map to generate the cursor in a CRT display. An unused portion of the memory is used to store a duplicate copy of the band in which the cursor is currently located, and the cursor is written into its appropriate location in this duplicate band, thus destroying the underlying image in the duplicate, but not in the original. The display is then generated by cycling through the page buffer except that the duplicate band containing the cursor, instead of the original band containing the underlying image, is displayed. After each display is generated, during the time when the scan returns from the bottom to the top of the display, if the cursor has moved since the previous display, the new band containing the cursor is created in the unused portion, and the display process is repeated.

Abstract: A process modification for the development of x-ray electrophotographic images with selenium photoreceptors wherein the occurrence of a catastrophic spot producing artifact called fatigue is eliminated. The process change consists of the addition of a photoreceptor pre-charging step immediately after thermal relaxation and before insertion of the photoreceptor in the elevator where it may be subsequently discharged by a suitable light source within thirty seconds of the pre-charging step. The effectiveness of the pre-charging step is achieved through field assisted detrapping of interference defect site injected holes which would otherwise detrap in the image charging step, thereby producing the fatigue artifact.