Abstract: When an array of photodetecting elements has to be calibrated, normally a reference surface is scanned. Yet the reference surface is not an ideal surface and likely may include scratches or dust particles so that the signals read out from the array have to be corrected. A method and system of correction are provided in which the statistical distribution of the signals read out over the surface is evaluated for each photodetector. By this evaluation, dust and scratches can be disregarded before calculating a mean value representative of the sensitivity of each individual element.

Abstract: A method of eliminating the effects of aliasing when printing objects having opposing edges. A center line between the opposing edges is identified. (FIG. 3). "Opposing pixels" on the edges are also identified and assigned offsetting grayscale values. (FIG. 4). This prevents the distances between the edges from appearing too narrow or too wide.

Abstract: Edge or contour information is extracted from an image array by filtering and encoded. In order to improve reproduction accuracy, two separate filters are used to detect edge information. One of the filters detects "sharp" edges, or edges in which the discontinuity in pixel intensity values occurs over a range of a few pixels. The other filter detects "level" edges in which the pixel intensity value discontinuity occurs over a larger range of pixels than the "sharp" edges. The "smooth" areas between edges or contours are assumed to vary continuously between the contours, but for efficient implementation, a one-dimensional linear interpolation is used to regenerate the contour information between edges. In addition, to further improve performance, a line is fitted to the pixel intensity data. The end values of this line are then used for the pixel intensity data.

Abstract: An apparatus and method for producing an enhanced resolution image from a set of lower resolution pixel image scans uses jitter and cogging errors introduced by the scanner to provide the additional information about the image that is required to produce the high resolution. One of the image scans is selected as a prototype image and is interpolated to produce an image of higher density samples (mixels). Each of the remaining pixel image scans is aligned with the interpolated prototype. The mixel values of the prototype are iteratively adjusted by minimizing an error metric representing the difference between pixel values computed from the prototype and the corresponding pixel values of each of the lower resolution pixel image scans. The method and apparatus are suitable for use in document copying system, high resolution television imaging, facsimile system, and character regeneration systems.

Abstract: A process is provided for avoiding a gap between adjacent uniform color objects in an image. First, it is first determined whether the image data contains two adjacent uniform color objects, each uniform color composed of two or fewer characteristic color components, and whether a gap would be evident between the uniform color objects. If the image data does not contain two adjacent uniform color objects with two or fewer characteristic color components or if a gap would not be evident, the image data is processed and output without adjusting the image. If, alternatively, it is determined that the image data contains two adjacent uniform color objects with two or fewer characteristic color components and a gap would be evident, at least one of the objects is examined to determine the saturation of each characteristic color component.

Abstract: An error diffusion method suitable for producing an output image from an input image having a set of digitized continuous-tone pixels is disclosed. The method includes the steps of computing an image activity signal; computing a set of activity weights from the image activity signal; computing a filtered input value for a digitized continuous-tone input pixel responsive to the activity weights and computing a filtered output value responsive to the activity weights for each of the possible output levels. The method further includes selecting the output level in response to the filtered input value and the filtered output value for each of the possible output levels according to an error criterion; determining an error signal between the filtered input value and the filtered output value for the selected output level; and weighting the error signal and adjusting the filtered input values for nearby pixels which have not yet been processed.

Abstract: An image transmission system includes an image transmitting unit having a display to display a status of a receiving unit and a detector for detecting a size of an original and a record mode permitted for transmission. A variable number of items of functional information together with a message that explains an operation of the system can be displayed, and respective input positions are provided for requesting the input of the functional information for the items. The number of items displayed then depends on the number of input positions operated.

Abstract: A filter achieving noise reduction and digital signal image edge enhancement includes two noise reduction circuits designed to enhance an image edge. The noise reduction circuits comprise both comparison units, which receive separate digital signals of an image and an inferential circuit connected to said comparison elements. Each inferential circuit uses a fuzzy logic unit designed to define activation levels based on signals generated by the comparison elements. The filter also includes a noise detection circuit and an image edge detection circuit both connected to the noise reduction circuit and designed to perform operations in accordance with fuzzy logic rules on the basis of the activation levels defined in the inferential circuits. The filter also includes a noise reduction circuit connected to the noise detection circuit and is designed to filter the digital image signals on the basis of the operations performed by the noise detection circuit.

Abstract: A system and method for processing image data converts a pixel of image data having a first resolution to a plurality of subpixels, the plurality of subpixels representing a second resolution, the second resolution being higher than the first resolution. The plurality of subpixels are thresholded to generate a group of subpixel values for each pixel and a threshold error value. It is then determined if the group of subpixel values from the thresholding process produce a pattern containing an isolated subpixel. If the group of subpixel values from the thresholding process produce a pattern containing an isolated subpixel, the group of subpixel vales is modified to produce a pattern without an isolated subpixel. The modification process produces a subpixel error value which is diffused in the slowscan direction to adjacent pixels.

Abstract: An apparatus for and a method of reliably detecting a very small dotted image area. A detecting area including a predetermined number of pixels including a target pixel is set. It is judged whether or not the detecting area belongs to a dotted image area on the basis of the number of edge pixels in the detecting area. Consequently, it is possible to detect edges peculiar to the dotted image area on the basis of a leading edge portion or a trailing edge portion of the density, to detect the very small dotted image area on the basis of the number of edge pixels.

Abstract: Information or data in the form of a mathematical representation of an area to be covered by a desired gray level, is sent, for example in floating point format, to a printer, e.g. a laser printer, for processing by the printer processor. The area to be covered is converted to a representation of pixels with the gray level converted to a digital value such as an eight bit value. Supercell representations with a gray level threshold matrix is provided, with each of the supercell array cells having threshold levels associated therewith whereby if the selected gray level is either above or below the threshold, one of print/no-print conditions are met for that pixel. Alternatively, if the level is the opposite and greater than a preselected range of values, the print/no-print condition will be opposite.

Abstract: An image processing method for converting multi-gradation image data into two-gradation image data by employing an error diffusion method, the image processing method comprises the steps of: (1) adding a diffusion error derived from at least one pixel which has already been binary-coded and is located near a pixel of interest to multi-gradation image data of this pixel of interest to thereby obtain corrected data; (2) comparing the corrected data with a threshold value and converting the corrected data into two-gradation image data for indicating any one of a dot ON and a dot OFF; (3) calculating a quantizing error corresponding to a difference between the corrected data and a first evaluation value corresponding to the two-gradation image data; (4) diffusing the quantizing error to a plurality of pixels which have not yet been binary-coded and are located near the pixel of interest; and (5) varying the first evaluation value corresponding to the two-gradation image data indicative of the dot ON in accordance

Abstract: A fuzzy device for image noise reduction, includes an interface adapted to retrieve the gray level of a pixel to be processed of an image and of neighbouring pixels; a difference circuit connected to the interface and adapted to generate a difference of the gray levels between said neighbouring pixels and said pixels to be processed; a fuzzy flat area smoothing circuit connected to the difference circuit and adapted to perform a low-pass smoothing of an almost homogeneous region defined by said pixel and by said neighbouring pixels; an edge preserving smoothing circuit connected to the difference circuit and adapted to perform low-pass filtering on a high-frequency information region defined by the pixel and by the neighbouring pixels; a region voter circuit connected to the interface and adapted to give a measure for considering whether the region defined by the pixel and the neighbouring pixels is almost homogeneous; and a soft switching circuit connected to the outputs of the smoothing circuit and adapted

Abstract: An image reading device selectively performs contrast adjustment on edge portions of the image, while suppressing contrast adjustment on noise and roughness of the image, thus obtaining a smooth and modulated image. Light emitted from a light source passes through or is reflected from an original document and is incident on a CCD line sensor, which outputs an electrical signal. This signal is input into an edge contrast unit, e.g., via a gain control amplifier, an A/D converter and a CCD signal processor. The edge contrast unit includes a computation unit by which edge contrast adjustment is accomplished selectively on input signals based on a comparison coefficient input from a comparison coefficient input unit and a contrast coefficient input from a contrast coefficient input unit. The resulting signal is stored in FIFO memory after passing through a normalizing processor, a DPI converter, and a LUT, for example.

Abstract: A system and process prints a high resolution image on a high addressable image output terminal by converting an image at one resolution to an image having a lower resolution in a fast-scan direction and a higher resolution in a pixel depth direction. The converted image is then processed and binarized prior to being printed on a high addressable printer. The system or process utilizes a conversion circuit which includes a two-bit per pixel packing circuit, a scanline buffer circuit, a logic circuit, and a look-up table. The conversion circuit initially converts the image into an image having a lower resolution in the fast-scan direction and a higher pixel depth resolution. Thereafter, the image is further converted to an image having a lower resolution in the slow-scan direction and a higher pixel depth resolution. This conversion of a high resolution image to a lower resolution is carried without any substantial lost to the image content data.

Abstract: In an image processing method for carrying out processing on an image signal, which represents a given image, the image signal is separated into low frequency components, middle frequency components, and high frequency components. Emphasis and restriction processing is carried out, with which the high frequency components are emphasized and the middle frequency components are restricted. The high frequency components and the middle frequency components, which have been obtained from the emphasis and restriction processing, and the low frequency components are combined with one another, and a processed image signal is thereby obtained. The image sharpness is thus emphasized, and noise components due to film graininess are removed, such that a reproduced image having good image quality may be obtained.

Abstract: A total of 2 N-1 serially connected delay circuits sequentially delay a digital image signal, where N is a positive integer, and a total of N-1 adders each respectively add a pair of delayed signals output from (N.+-.k)-th ones of the 2 N-1 delay circuits, where k is an arbitrary positive integer such that k<N, while a selector is responsible for a boost frequency to select an output signal of one of the N-1 adders. A first multiplier multiplies the selected signal by a first coefficient, a second multiplier multiplies an output signal of an N-th one of the 2 N-1 delay circutis by a second coefficient, and another adder synthesizes output signals of the first and second multipliers.

Abstract: A document processing system is provided for processing a job having one or more electronic pages with at least one of the electronic pages including a set of pixels defining a halftone image. Each pixel is disposed in one of a first state and a second state, and the set of pixels includes a plurality of dots with each dot including a group of one or more pixels disposed in the first state. The document processing system includes an image examination system for determining whether a first dot and a second dot exist within a selected subset of one of the one or more sets of pixels. When the image examination system determines that the first and second dots exist in the selected subset, the image examination system determines whether the first dot includes more or less pixels disposed in the first state than the second dot.

Abstract: A method and apparatus that convert a series of drawing instructions, suitable for assigning pixel values corresponding to the drawing instructions to an image arranged in rows and columns of pixels, to a series of runlengths and corresponding pixel values. A runlength represents the number of successive pixels with mutual identical pixel values while the series of runlengths and pixel values is arranged according to a first order as determined by successive pixel positions. The runlengths of the pixel values (as generated by the drawing instructions) are determined in a second order which is different from the first order. Consequently, the insert positions of these runlengths are determined on the basis of pixel positions which correspond with said determined runlengths.

Abstract: An original image signal, which represents an original image and is made up of a series of original image signal components representing picture element values of picture elements arrayed at predetermined intervals and in a lattice-like form, is obtained. One of different interpolating operation processes is carried out on the original image signal and in accordance with an image size enlargement scale factor with respect to the original image, which is represented by the original image signal. An interpolation image signal is obtained from the interpolating operation process, which signal is made up of a series of image signal components, which occur at intervals different from those of the original image signal components. The response of an interpolation image, which is reproduced from the interpolation image signal and displayed on an image reproducing apparatus, is kept to be approximately equal to a predetermined level regardless of the image size enlargement scale factor.

Abstract: A system calibrates a computer print image. A page driver receives an image having image properties, such as color scheme, image resolutions, contrast, etc., and sends it to a journal file for storage. A user interface enables selection of a property of the image. A journal file processor generates specific values based on a selected range of values for controlling the characteristics of the selected property. A rendering driver renders a modified version of the image for each generated value, and sends the modified versions to the printer. The user interface enables the selection of a preferred image from the rendered modified images. The journal file processor sends the values of the selected image to the driver settings file for storage.

Abstract: A printer control system for controlling a print characteristic of a printer for printing a print pixel signal synchronized to horizontal lines of an image. The print pixel signal has an arbitrary horizontal resolution and includes white print pixel signals representing white pixels of the image and black print pixel signals representing black pixels of the image.

Abstract: A resolution conversion system for real-time expansion and reduction of a first plurality of input pixels into a second plurality of output pixels. The resolution conversion system comprises a base-n counter for counting input pixels as each pixel is captured. The base-n counter has a plurality of carry out signals. Also, there is a control register for selectively enabling the carry out signals of the base-n counter based on a predetermined resolution ratio between the first plurality of input pixels and the second plurality of output pixels. The control register uses a mode bit to select either one of inserting and removing operations. An inserting logic unit is used for inserting, as indicated by the mode bit, a pixel into the plurality of input pixels upon a transition of one of the carry out signals if the carry out signals have been enabled by the control register.

Abstract: Data processing method and apparatus for converting data such as character data or image data of a resolution X into data of a resolution Y which are effective for use in, particularly, a recording apparatus such as an ink jet printer or the like.

Abstract: A method and system implements a redistributive characteristic into an error diffusion process. A grey level value representing a pixel is received. A threshold circuit thresholds the received grey level value and generates an error value as a result of the threshold. A portion of the error value is diffused to adjacent pixels on a next scanline. All the error for a single pixel on the next scanline is accumulated. Since this accumulated error has a greater number of bits than can be stored in a buffer, a portion of the accumulated error is truncated and redistributed to a down stream pixel for inclusion in the downstream pixel's error accumulation process. The grey level value has a first resolution which corresponds to an original input resolution. In a high addressabilty environment, the received grey level value is interpolated to subpixel grey level values before thresholding.

Abstract: An image preprocessing method and apparatus processes image data line-by-line using an error diffusion process to generate a halftoned image. The method and apparatus varies the processing direction from line-to-line to minimize the presence of worm-type artifacts in a halftoned image where the processing direction of each line in the image is dependent on the content of the image. More particularly, the processing direction of each line in the image is dependent upon the grayscale value and/or the quantization error associated with one or more pixels of a previously processed line in the image.

Abstract: When a frame marked with a marker pen in a black-and-white image is to be extracted, an intermediate-density portion present on a character edge portion is removed by a frame extracting circuit. The frame extracting circuit removes an intermediate-density pixel adjacent to a high-density pixel corresponding to a character/figure. Accordingly, the extracting precision of the marker portion in the black-and-white image is improved. The extracting precision of the marker portion will not be decreased even when extraction is to be performed from an image enlarged by an input system.

Abstract: An apparatus for processing original image data to produce print image data used by a printer, wherein a data bus switching circuit provided between an original image data memory and a shift register is selectively placed in a 1X mode or an NX mode. In the 1X mode, each bit of the original image data is transferred as a bit of the print image data to the shift register without conversion. In the NX mode, each bit of the original image data is converted into N (.gtoreq.2) number of bits of the print image data which have the same logical value equal to that of the original image data bit. The addresses of the shift register at which the print image data are sequentially stored are designated by an address counter based on a mode select signal and a write command for reading a set of the original image data for one line from the original image data memory. A read signal is generated for reading out a next set of the original image.

Abstract: According to the invention, video data which are incapable of sufficiently reducing toner consumption through thinning-down control inclusive of edge detection, is divided into unit elements to increase the apparent dot matrix number of each letter or character, and the unit elements thus obtained are reconstituted through an image smoothing process or a pseudo image density increasing process for thinning-down control again. When a pixel is divided into four divisions, for instance, substantially the same effect as of thinning-down control of a letter of apparently four times the size is obtainable. Dense thinning-down control is thus obtainable.

Abstract: The present invention is a method and apparatus for mapping digital image data using paired erosion-based filters. One filter of the pair creates a superset of the output image data and the other a subset of the output image data, and combinatorial logic is then applied to the superset and subset data to obtain the mapped image data. In one embodiment a plurality of erosion-based filters are used where one filter of the pair is extensive and the other filter is antiextensive, each pair generating a sample phase of a high resolution output image.

Abstract: Image data of an original image in a prescribed pixel matrix is subjected to edge emphasis. On the other hand, a maximum and a minimum of the image data are detected. Then, values of the image data subjected to edge emphasis are limited between the maximum and the minimum to provide output data. Thus, edge emphasis can be performed without increasing noises even for hand-written characters of low densities.

Abstract: A system and process prints a high resolution image on a high addressable image output terminal by converting an image at one resolution to an image having a lower resolution in a fast-scan direction and a higher resolution in a pixel depth direction. The converted image is then processed and binarized prior to being printed on a high addressable printer. The system or process utilizes a conversion circuit which includes a two-bit per pixel packing circuit, a scanline buffer circuit, a logic circuit, and a look-up table. The conversion circuit initially converts the image into an image having a lower resolution in the fast-scan direction and a higher pixel depth resolution. Thereafter, the image is further converted to an image having a lower resolution in the slow-scan direction and a higher pixel depth resolution. This conversion of a high resolution image to a lower resolution is carried without any substantial lost to the image content data.

Abstract: The invention provides an apparatus for enhancing full color images and may be used within a variety of computer peripheral devices such as a scanner which scans images initially recorded on a photographic medium, for example. The invention takes image data and applies a programmable set of parameters to the image data which govern color saturation and sharpness, inter alia. The image is then passed to a computer where a user may alter the parameter. The parameters are passed back to be reprocessed within the scanner and an updated image is then sent back the computer in real time.

Abstract: An improved error diffusion method for incorporating into a halftoning algorithm for processing gray scale images to counterpart binary images. The improved error diffusion method adopts a tone scale function to process the input gray scale image before proceeding with the halftoning (error diffusion) processing in order to improve the image darkening problem caused by the conventional error diffusion method and a noise correction process to eliminate the background noises resulted from the accumulated error of the conventional error diffusion method. The proceeding of the tone scaling process and the halftoning process are parallel with the correction process so that errors generated in either one will not affect the other.

Abstract: A bit-map unit forms a bit map using given image data. A boundary recognizing unit recognizes characteristics of a boundary present between a first type of pixels and a second type of pixels constituting the bit map. A determining unit determines for each pixel whether a correction is necessary so as to make an image produced from the given image data significantly finer. The determination uses at least part of the boundary characteristics. A correction unit performs a correction on image data for each pixel needing the correction. The correction is performed in a manner determined depending on the relevant boundary characteristics. A data replicating unit replicates the given image data to produce copies of the image data in addition to an original of the given image data, the correction unit performing the correction in different manners between the original and copies of the given image data.

Abstract: An apparatus processes two-tone image data so as to magnify a relevant image and smooth a boundary line between a zone consisting of first-tone pixels of two-tone pixels constituting the relevant image and a zone consisting of second-tone pixels of the two-tone pixels. The apparatus is characterized in that the apparatus comprises a unit which, for each two-tone pixel of the two-tone pixels, determines a template pattern, from among a plurality of template patterns, as matching a pixel arrangement comprising pixels located around the each two-tone pixel; and a unit for converting the each two-tone pixel into either single multiple-tone pixel of plurality of multiple-tone pixels, the unit using a result of the determination performed by the unit for the converting.

Abstract: A method and system implements a high addressability characteristic into an error diffusion process. A grey level value representing a pixel is received: The grey level value has a first resolution which corresponds to an original input resolution. The grey level value is interpolated to generate subpixel grey level values which correspond to a second resolution. The second resolution is higher than the first resolution and corresponds to the high addressability characteristic. A threshold circuit thresholds the interpolated grey level value and generates an error value as a result of the threshold. The error value has a resolution corresponding to the first resolution. A portion of the error value is diffused to adjacent pixels on a next scanline.

Abstract: A method processes a plurality of bits stored in a first memory and representing an image to be printed by reproducing the bits in a fast scan direction. The method includes the step of reading a plurality of groups from the first memory into a second memory, wherein each of the groups comprises a number of bits greater than one bit and is stored in the second memory in the fast scan direction, and wherein each group is read one group at a time. Further, the method includes copying a predetermined number of bits from each of the plurality of groups to a sample storage area. After the copying step, the method samples the bits of the copied groups wherein the sampled bits form a pattern having a center bit having a binary state. Finally, after the sampling step, the method outputs a print signal representative of the binary state if the pattern does not match a predetermined pattern, or outputs a print signal different than the binary state if the pattern matches a predetermined pattern.

Abstract: An image reading apparatus such as a color copying apparatus has a plurality of sensing CCD chips for converting an image of an object into an electrical signal, each sensing CCD chip having a plurality of sensing elements. The apparatus also has a circuit for converting the electrical signal into digital data. A first adjusting circuit is provided for conducting either an operation for obtaining level matching of the electrical signal converted by the sensing chips, or an operation for controlling the gain of the electrical signal converted by the sensing chips.

Abstract: An image processing apparatus obtains image data with a low resolution by processing a plurality of pixel values read in with a high resolution into one pixel value, for the low resolution mode. Thereby, the image processing apparatus is able to transmit unfailingly image data needed for reproduction of a narrow line in a document even during a low-resolution mode. Further, in accordance with a resolution mode that is currently selected, an image processing apparatus adjusts the ratio between the amount of edge enhancement with respect to the main scanning direction and the amount of edge enhancement with respect to the sub-scanning direction, thus unfailingly including the image data needed for reproduction of a narrow line extending in the main and/or sub-scanning direction.

Abstract: A method of improving the contrast in a natural scene image. A relevant histogram of the image is derived for from a selected subset of local histograms representing regions of the image. The signal describing the histogram is operated on with a filter having the characteristic of weakening strong peaks and valleys in the function, but not effecting flat portions of the signal. The filtered histogram signal is used for controlling the TRC mapping in a device at which the image is to be printed. To assure optimum selection of local histograms, regions including the black point and white point of an image are determined and added to the subset of local histograms representing regions of the image.

Abstract: A graphics accelerator decides pixel densities using an anti-aliasing process for left and right edges of a figure in an image, and for sending resulting pixel density data to a frame memory. The apparatus includes a memory read/write controller inputs a contribution ratio, a density value, a "y" coordinate for a raster line, a start coordinate x.sub.1, and an end coordinate x.sub.2, and sends an address to the frame memory. A LUT provides pixel densities based on the contribution ratio and the density value. Three contiguous pixels' densities are latched, including densities for a middle pixel and two outer pixels.

Abstract: In a run-length represented image an image area with reverse print is recognized. Two borders (left and right) are determined and in a plurality of steps the run transitions are removed, first on the left border of the area and then at the right border of the area, causing all runs within the area of reverse print to take on the reverse color.

Abstract: A technique involving the standardization of the subject matter of an image and the compression of the image using features of the standardization can provide for a high compression ratio. This technique can be used to improve the quality of a restored image for a predetermined amount of storage space.

Abstract: An improved method for providing a more faithful and pleasing rendition of a pixel pattern is described herein. This method first places the original pixel pattern in a bit mapped memory. A small portion of this bit mapped pattern, called an input tile, acts as an address for a look-up table containing a corrected pixel pattern portion (an output tile) corresponding to the target pixels to be corrected in the input tile. To derive the output tiles stored in the look-up table, a high resolution bit map is created from an input tile by scaling the input tile. A triangular portion of each convex corner in the high resolution bit map is chopped off, and a triangular portion of each concave corner in the high resolution bit map is filled in. The resulting pattern is then smoothed using a low pass filter. The size of these triangular portions and the extent of low pass filtering are determined using a function based on the vulnerability of a pixel to being eliminated during the above smoothing process.

Abstract: A method, system and process for improving image enhancement tools through the application of expert systems. The improvements are accomplished by the operation of a process in the memory of a processor that enhances an image based on a set of criteria entered by a user. The image is enhanced in at least two ways and the two enhanced images are presented to the user. The user selects the image that appears best and the selected image is thereafter used for subsequent image enhancements according to the user criteria until a final image is created.

Abstract: An image outline filling system comprises an image outline memory for storing start positions and end positions of image outlines, and a controllable arithmetic circuit which changes its output status in a positive direction at a start position of the image outlines and changes the output status in a negative direction at a end position of the image outlines. By filling a region in which the output status has a value of the positive direction, the image outline whose inside is filled is obtained.

Abstract: In an image processing apparatus, images on an original document captured by an image capturing device are classified into a binary image and a gradation image, and the densities of the images are then converted using density conversion curves, which are provided for binary images and gradation images, to output an image signal representing converted images. The state of a certain pixel is judged and is classified as one of a plurality of states between binary images and gradation images. Based on the results of the judgment, one curve is selected from a first density conversion curve for binary images, a second density conversion curve for gradation images and at least one third density conversion curve which interpolates the first and second density conversion curves. The density of the certain pixel is converted using the selected curve.

Abstract: In an image processing apparatus, digital video data is converted into analog video data by a D/A converter. A reference pattern timing-adjusted is generated. The phase relationship between the reference pattern and the analog video data is optimized. The analog video data and the reference pattern are compared by comparing unit. A pulse-width modulated signal output from the comparing unit is detected. The variable output regulator is controlled according to a preset reference value, a quantity of laser light of the output device, or a surface potential of the photoreceptor. Through the control of the regulator, the quantity of bias applied to the reference pattern is optimized at all times, providing a pulse-width modulated image signal with an excellent tone reproduction at all times.

Abstract: A scanner having an image sensor unit having a CCD linear array for electro-optically scanning an image of an original in a main scanning direction to convert the image into image data signals is used to scan, through a table sheet having a transparent document area and a pattern area which includes a stripe pattern inclined with respect to the main scanning direction, an original placed under the document area to read data of the original, and the scanner is moved relative to the original in a subscanning direction perpendicular to the main scanning direction. A pattern signal obtained by scanning the pattern area then is analyzed to detect an amount of relative movement of the scanner in the subscanning direction from the movement of the stripe pattern in the main scanning direction.