Abstract: A method for generating a binary representation of an image represented in half-tone form is described in which the image is scanned and sampled, and in which each pixel corresponding to a sample of the image is assigned one of two colors. The method comprises, for each group of abutting and non-overlapping sampled pixels, determining the number of pixels in the group which are to be assigned to each of the two colors (step 13); allocating a unique sequence to the pixels (step 15); and assigning one of the two colors to pixels in sequential order until the predetermined number of pixels of that color has been assigned (step 16) and thereafter assigning the other color to the remaining pixels in the group (step 17).

Abstract: A scan apparatus, comprising: a platen on which a document can be placed; a criterion member on which at least one black zone and at least one white zone are formed successively in the subscan direction, criterion member being arranged near the platen on the side from which a subscan is started; a device for detecting a linear optical image of the document to obtain the density distribution of the linear optical image; a device for scanning the criterion member and a document in the subscan direction which includes a device that illuminates a document placed on a document area of the platen and the criterion member; and a device for determining a reference timing for starting a scan of the document on the platen, which is connected to the device that detects a linear optical image so as to detect a boundary between the black and white regions and determine the reference timing from the boundary detected.

Abstract: Apparatus and methods for converting continuous grey tone images into high resolution halftone images utilize an iterative, multi-level, multi-resolution error convergence process. The continuous grey tone image is first binarized. At each level of the process, the binarized image is compared with the grey tone image over a larger window of pixels. Within each window, selected binarized image pixels are tested for possible change in binary assignment. The binary assignment of a given test pixel is changed if the change would result in a lower average error over the entire window. By varying the selection of test pixels, the process can provide clustered dot patterns and dithering.

Abstract: An image processing apparatus of this invention is arranged so that a threshold for use in binarization is switched between two types in accordance with whether or not a portion in which input pixel data is located is positioned in the vicinity of an edge portion of an image. One type is a threshold which varies in the width of variation corresponding to the density of the input pixel, while the other type is a fixed threshold. If an objective pixel is located in the vicinity of an edge portion of an image, binarization is carried out with the fixed threshold, while if the objective pixel is located in a non-edge portion, the variable threshold is used.

Abstract: An apparatus converts a multi-density image into a binary value image by converting pixels with densities above a threshold to a first value and pixels below a threshold to a second value. The apparatus generates a histogram relating image densities with the numbers of pixels having those densities. A first memory holds the image pixel densities. A second memory has address inputs attached to the data outputs of the first memory. Addresses of the second memory correspond to image densities. As a pixel is read out of the first memory, its density value serves as an address for a location in the second memory, and a count stored in that address is incremented. After reading all of the pixels from the first memory and incrementing counts, the second memory holds a histogram of the image. The apparatus evaluates the histogram to identify a density for which the number of pixels in the image is a local minimum. The local minimum is selected as the threshold.

Abstract: Apparatus for converting multilevel video images into a bilevel image having an accurate rendition of the original grayscale of the image. The apparatus can provide an improved rendition of low contrast images.

Abstract: An image scanner for producing a halftone image is provided with a halftone signal generator which generates an exposure signal (S) for controlling the exposure duration of a laser beam (L) which beam is focused on a photosensitive material. The halftone signal generator is so constructed that image data (N) is compared with a threshold data (screen pattern data) for each elementary area and the exposure duration for each elementary area is determined mainly according to a difference between the image data and the threshold data. Some of the elementary areas are partially exposed, to an extent which depends on the exposure duration.

Abstract: According to an image signal processing apparatus in accordance with the present invention, an input signal is converted to a digital image signal and then the digital image signal is cyclicly shifted. Therefore, a desired signal component can be collected on a first or second level side. Therefore, a signal can be divided into bilevels in reference to one threshold value or it can be divided into multiple levels in reference to a plurality of threshold values. As a result, it is possible to precisely extract contours of the image signal even if there is a small density difference between a background signal and an information signal. In addition, a background can be converted between white and black.

Abstract: A halftone conversion system for converting digital pixels to binary pixels in which individual matrices in a memory having progressively changing x, y matrices of binary pixels are addressed by an address composed of a block of x pixels including the pixel being processed, a block of y lines including the line containing the pixel being processed, and the digital value of the pixel being processed, the pixel located at the x, y coordinates of the addressed matrix providing the binary pixel output.

Abstract: Apparatus for converting multilevel video images into a bilevel image having an accurate rendition of the original grayscale of the image. The apparatus performs enhanced preservation of edge information in the image when using error diffusion techniques.

Abstract: An apparatus for converting an analog image signal to a digital image signal based on a reference voltage, includes a counter having a control terminal, for counting a first signal and outputting a counted value in digital form, a D/A converter for converting the counted value to an analog voltage signal served as the reference voltage, an A/D converter for converting the analog image signal to the digital image signal based on the reference voltage generated by the D/A converter, and a comparator for comparing in magnitude the digital image signal and a threshold level used for limiting the magnitude of the digital image signal, thereby outputting a control signal based on the results of comparison. The counter continues to count the first signal until the control signal derived from the comparator is supplied to the control terminal of the counter.

Abstract: Thresholding and background referencing apparatus are disclosed for use with apparatus for scanning documents having images with object and background regions. The background referencing apparatus receives, from the scanning apparatus, a video signal representing the document image and generation a signal having a value representative of an estimate of the background density level of the document being scanned. The apparatus produces a difference signal representative of the difference between the estimated background level signal and the received video signal. The estimated background level signal is stored, and updated in response to (1) the difference signal being of a first sign associated with transition from object to background, and (2) only small difference signals of a second sign associated with transition from background to object, whereby large difference signals of the second sign result in substantially no change in the stored estimated background level signal.

Abstract: A half-tone binarization generator that produces high-quality half-tone binarization images by converting multilevel brightness information into sets of black and white bitonal data by adding noise to the multilevel brightness information and using a thresholding technique.

Abstract: An image processing apparatus comprises a pulse-width-modulation signal generator for processing an image signal generated by an image signal generator by using a pattern signal to produce a pulse-width modulation signal. The pulse-width modulation signal generator generates first and second pattern signals of different periods, selects one of the pattern signals in accordance with a property of an image to be processed, and inhibits the generation of the non-selected pattern signal.

Abstract: A half tone display apparatus using a display apparatus of bilevel representation in white and black is provided. The apparatus includes a unit supplied with a multilevel image such as a color image, a device for detecting edges in characters, patterns and photographic images, a unit for deriving a level difference between pixels adjacent to the edge, and a control unit for forcibly displaying a pixel of the edge portion as a white or black pixel for emphasis provided that the level difference is not larger than a predetermined threshold and for applying dither conversion to other pixels.

Abstract: Apparatus for enhancing and thresholding scanned microfilm images, specifically for removing single pixel noise therefrom, and accompanying methods for use therein are disclosed. Specifically, this apparatus convolves each one of a pre-defined group of incoming pixel values with a corresponding one of a pre-defined set of coefficients in order to generate an convolved pixel value. The convolved pixel is then compared against a threshold level to produce a thresholded pixel value indicative of the results of the comparison. The inventive apparatus also includes a noise processing circuit that contains a noise tracker and a noise detector and filter circuit. The noise tracker is used to produce a noise value that tracks a noise level present in the threshold pixel value.

Abstract: A scanning device which is capable of scanning documents at high speeds and high resolutions. The present invention uses automatic thresholding techniques and provides variable data compression to accommodate various end user host devices. The present invention is entirely menu driven and utilizes a cursor control and enter button to select the various options available through software.

Abstract: False contouring of a screened halftone image without including more sub-elements in each cell, increasing the size of each cell, or decreasing the screen frequency of the image is accomplished by assigning to each sequential sub-element of a halftone cell a weighted probability of being "ON" in accordance with the value of the associated input signal.

Abstract: An image processing apparatus includes a photoelectric converter, a multiple-value circuit, and a detachable external storage unit. The photoelectric converter photoelectrically coverts data of an original into image signals. The multiple-value circuit converts the image signals into multiple-valued data by comparing the image signals with predetermined threshold value data. The detachable external storage stores the threshold value data. The threshold values can also be made automatically responsive to gray scale data. The automatic mode and the manual selection mode are switched between in response to a release (toggle) signal. Color separation and color ghost correction are provided; and various types of formatting management are faciliated. Partial color converting (as, for example, color reversal) is also provided.

Abstract: Apparatus is disclosed having document recognition capability for determining the size and location of an original document on a scanner platen before the document is scanned for image capture, and which effects both document recognition and image capture within a single scan cycle. A platen is optically scanned in forward and reverse intrack directions, and an electrical information signal characteristic of the optical densities scanned is created. Document recognition is responsive to the electrical information signal produced during the forward direction scan for detecting the boundaries of an original document on the platen. Image capture is responsive to the electrical information signal produced during the reverse direction scan for producing a record of the image on the original document.

Abstract: This invention relates to an apparatus for converting a grayscale image to a bitonal image which provides improved tonal rendition with minimal loss of resolution. The invention attenuates the low spatial frequency component of the digital image and uses a similarly attenuated thresholder to convert the image to a bitonal image. When used with a dither type thresholder, this technique allows for simultaneous "continuous tone" and "line art" thresholding with minimal circuit complexity.

Abstract: This invention relates to a method for converting a grayscale image to a bitonal image which provides improved tonal rendition with minimal loss of resolution. The invention attenuates the low spatial frequency component of the digital image and uses a similarly attenuated thresholder to convert the image to a bitonal image. When used with a dither type thresholder, this technique allows for simultaneous "continuous tone" and "line art" thresholding with minimal circuit complexity.