Abstract: An image signal (PS) or a screen threshold value (D) is converted by a plurality of conversion functions (F.sub.i, G.sub.i, f.sub.i, g.sub.i). The number (N.sub.ST) of reference solid pixels, which should be exposed to attain a halftone area rate specified by a given image signal, is calculated for each quarter block (QB) which is a quarter of one unit block for one halftone dot. The numbers (N.sub.RS) of virtual solid pixels, which would be exposed if the converted image signal or the converted screen threshold value were used, are calculated concerning respective conversion functions for each quarter block. The number (N.sub.RS) of virtual solid pixels which is the closest to the number (N.sub.ST) of reference solid pixels is selected and the conversion function corresponding to the selected number (N.sub.RS) is also selected for each quarter block (QB).

Abstract: Method for transforming a video type image having multiple levels of greys into a binary image, method wherein each pixel is either white or black. With each pixel of the initial image there is associated a partial image centered on said pixel and comprising a plurality of pixels in at least one dimension. If the histogram of the grey levels of said partial image is considered as bimodal (D>E), a threshold (S) median with respect to said histogram is selected. If the histogram is considered as monomodal (D<e), a threshold (S) outside said histogram is selected, the position of this threshold with respect to the histogram being determined by comparison of the latter with a preset mean background value (FM). Application to telecopy, electronic storage of documents and drawings, preprocessing in order to facilitate the reading of handwritten messages or recognition of patterns in general.

Abstract: An image processing apparatus such as a digital printer or digital facsimile apparatus for half tone processing input image data has: an input device to input image data indicative of a concentration of an image; a discriminating circuit to discriminate whether the input image data is smaller than a threshold value or not; a binarizing circuit to binarize the input image data into binary data of high and low levels; and a setting circuit to set the binary output of the image data to the low (0) level irrespective of the result of the binarization by the binarizing circuit when the input image data is determined to be smaller than the threshold value. The input device includes a reading circuit to read the original image and a generator to generate image data indicative of the original image concentration.

Abstract: The background compensation circuit defines a background threshold signal in dependence on an average value between the positive-peak and negative-peak signals previously received from the elements for scanning the pixels of the image, and in dependence on the analog signal (AS) of the pixel added to a reference signal. The circuit comprises two detectors (21, 22) for respectively detecting a positive peak and a negative peak and which each have a short charge time constant and a long discharge time constant. A summing circuit (25) generates a threshold signal (V.sub.s) as a linear combination of the signals (V.sub.max, V.sub.min) of the detectors (21, 22) the analog signal (AS) of the pixel and a reference signal (V.sub.r). Finally the threshold signal is compared (26) to the analog signal (AS) of the pixel to produce a binary reading signal which is at "one" level when the threshold signal is greater than the analog signal and is at "zero" level when the threshold signal is less than the analog signal.

Abstract: A document scanner for utilization with a word processing and/or graphics processing equipment, such as a personal computer environment. The document scanner provides improved pixel compensation and gamma compensation techniques as well as improved control in the illumination process of the scanning of a document.

Abstract: An image binarization system in which the threshold value used for the binarization process can be adjusted to thereby enable the process to be made more accurate and avoid loss of black areas in characters in the process of digitizing and conversion. The threshold value is based on the average value of pixel density values around the pixels to be binarized, and is corrected downward when the average density value of the surrounding pixels is larger than a specific boundary value, and upward when the average value is smaller than the said boundary value.

Abstract: An image reading apparatus for converting an image on a document having a white/black text area into a display signal. An image reader scans pixels forming the image to produce a read signal having a level corresponding to the brightness density of each of the scanned pixels. The read image is compared with a dither matrix data signal and converted into a dither converted signal. The read image is also compared with a threshold value and converted into a binary signal having a first level representing a white pixel and a second level representing a black pixel. A discrimination circuit receives the binary signal for producing a detection signal when the white/black text area is scanned. Upon occurrence of the detection signal, the dither converted signal is mixed with the binary signal to form the display signal.

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.

Abstract: An adaptive thresholding technique is calculated by using a real-time 16 pixel running average (RA) 18 to which is added on offset value. The offset value 38 is the product of a programmable factor (alpha) and a Sum Absolute Difference (SAD) noise measurement. The adaptive threshold 42 is compared by a comparator 48 with a delayed analog video signal intensity value on line 46 for the pixel associated with the adaptive threshold. The comparator 48 provides a binary video output for further processing. A relative video output may also be provided by taking the difference of the analog video signal 46 and its corresponding running average 18.

Abstract: There is an image processing apparatus for use in a facsimile, electronic file, reader, digital copier, or the like. This apparatus has an image discriminating function and a high operating speed and comprises a pixel data input circuit and a circuit for processing the pixel data inputed from input circuit, in which the processing circuit has a discriminating circuit for detecting an amount of change in density level of the input pixel data for every pixel and discriminating the content of the image of the objective pixel data and a selector for selecting the processing mode of the projective pixel data in accordance with the result of the discrimination. Either half-tone processing mode or the non-half-tone processing mode is selected by the selector on the basis of the result of the discrimination. The non-half-tone processing mode is continuously selected for a determined period of time irrespective of the result of the discrimination.