Dainippon Screen Mfg. Co., Ltd.

Dainippon Screen Seizo Kabushiki-kaisha

Kunio Ikuta

Masayuki Murai

Hitomi Atoji

Katsunori Yamada

Error data .SIGMA.e.sub.P accumulated for a target pixel of binary coding or pixel of interest P is read from an error memory (20) and inputted into an adder (22). The adder (22) adds the error data to multi-valued image data regarding the pixel of interest P, so as to correct the multi-valued image data. A comparator (24) compares the corrected multi-valued image data outputted from the adder (22) with a predetermined reference value and outputs binary image data based on a result of the comparison. A bit converter (28) converts the one-bit binary image data to 8-bit data. A subtracter (26) subtracts the binary-coded image data from the image data prior to binary coding to obtain an error `e`. An error distribution circuit (30) distributes the error `e` into pixels A, C, D, and E, where the pixels A, C, and D are respectively located on the immediate right of, immediately below, and on the lower left of the pixel of interest P and the pixel E is located on the immediate left of the pixel D. The error memory (20) adds distributed portions of the error e.sub.A, e.sub.C, e.sub.D, and e.sub.E to error data .SIGMA.e.sub.A, .SIGMA.e.sub.C, .SIGMA.e.sub.D, and .SIGMA.e.sub.E, so as to update the values of the error data .SIGMA.e.sub.A, .SIGMA.e.sub.C, .SIGMA.e.sub.D, and .SIGMA.e.sub.E. This method of distributing the error `e` into the above peripheral pixels enables multi-valued image data for the pixel of interest P having a relatively low tone value or a relatively high tone value to be binary coded without damaging the quality of picture.

Method and apparatus for binary coding of image data including adding

The present invention produces a set of improved halftone images which effectively prevents occurrence of rosette moire. A plurality of parallelograms can be formed from three apexes consisting of an arbitrary first apex of a reference triangle RT1, a middle point of the side of the triangle facing to the first apex, and one of the other two apexes of the triangle. One of the parallelograms is selected as a unit area for one halftone dot. The unit area is virtually laid out repeatedly on an image plane, and one halftone dot is located with respect to each unit area. Each halftone dot can be located at the center of the unit area or at any desirable position in the unit area.

Method of and apparatus for recording halftone images

Three or more conversion functions are prepared. Only a part of the conversion functions are extracted therefrom to specify provisional conversion functions. A reference solid-pixel number and imaginary solid-pixel numbers for each provisional conversion function are computed through an imaginary exposure for a quarter halftone-dot block on a scanning line. The imaginary solid-pixel numbers are computed in response to new image signals which are obtained by converting an image signal through the respective provisional conversion functions. Then, each of the imaginary solid-pixel numbers is compared with the reference solid-pixel number, thereby a most-approximate conversion function, which gives a solid-pixel number most approximate to the reference solid-pixel number, is selected among the conversion functions. An exposure control signal is generated by comparing an image signal which is obtained by converting the image signal through the most-approximate conversion function with a corresponding screen threshold value.

Method of and apparatus for obtaining halftone image

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). Photosensitive film is exposed on the basis of the converted image signal or the converted screen threshold value converted by the selected conversion function, whereby the halftone area rate specified by the given image signal is attained, and the line portion is prevented to be seen broken.

Method of producing halftone images by choosing a conversion function

A film coordinate generator generates film coordinates (u, v), corresponding to the position of an exposure beam on a recording film which is detected by encorders, which is in turn supplied to a screen coodinate generator to be converted into virtual screen coordinates (x, y). A beam control signal generator receives the coordinates (x, y) and an image signal corresponding to the position of the exposure beam to output a beam control signal indicating lighting of the exposure beam when one of the coordinates (x, y) is in between upper and lower limit values, corresponding to the same, which are previously decided for each combination of the other of the coordinates (x, y) and the density value of the image signal.

Halftone dot-generator and generating method

Halftone dots are formed pixel by pixel onto a photosensitive film of a size P.times.P in an improved manner by using a screen memory storing thresholds, each of which corresponds to each of m.times.n sub-cells of a halftone dot area of the size S.times.S. In accordance with the invention, four table memories are prepared by respectively storing values ##EQU1## with y.sub.n being the main scanning direction addresses and x.sub.n being the sub-scanning direction addresses. Values read from the first table memory and values read from the second table memory are summed to obtain the sub-scanning reading addresses of the screen memory, while the values read from the third table memory and the values read from the fourth table memory are summed to form the main scanning reading addresses of the screen memory. At this junction, the values (1) to (4) to be stored in each of the table memories are permitted to be residues, taking advantage of the characteristic that the values are periodic. Additionally, the memory capacity required for the operation can be permitted to be smaller by taking advantage of the characteristic that the values of interest form an arithmetic series.

Method of and apparatus for forming the address signals of a screen

In reproducing halftone dot images, the appearance of moire effect is suppressed by slightly and randomly disarranging the positions of halftone dots to be recorded from the normal position in each unit halftone dot area, or by slightly and randomly distorting the halftone dots.

Halftone dot formation

A tint laying device for use in a picture reproducing machine, wherein a pickup head scans an original picture to pick up a picture signal and sends it to a color discriminator which discriminates a color in hue of the picture signal to output a discrimination signal to a halftone dot area rate controller, wherein the controller outputs a signal corresponding to a halftone dot area rate predetermined of a halftone dot to be recorded, per each color, to an exposure amount controller which varies the brightness corresponding to the halftone dot area rate depending on the signal output from the controller, and wherein an exposure head scans a recording film and records a reproduction picture thereon according to the halftone dot area rate in synchronization with the pickup head. This device is capable of performing an accurate and quick operation without any skill.

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Kyoto, Japan

Kunio Ikuta