Dainippon Screen Mfg. Co., Ltd.

Dainippon Screen Manufacturing Co., Ltd.

Nobuaki Usui

Atsushi Imamura

Takashi Sakamoto

Hiroki Fujimoto

Shigeaki Shimazu

Kazutaka Taniguchi

Kazuhiro Nakai

Tetsuo Asano

An illuminance spectrum I of reflected light from a color print of an N-order color having an arbitrary dot percent d.sub.1-N is defined by a diffuse reflection coefficient Sb(d.sub.1-N,.lambda.) and a specular reflection coefficient Ss(d.sub.1-N,.lambda.). These reflection coefficients are obtained in the following manner. A plurality of reference colors are specified on each of N.times.2.sup.(N-1) sides that constitute an N-dimensional color space including the N-order target color. Each reflection coefficient is expressed by a linear combination of a plurality of reference reflection coefficients Sb and Ss, which are set in advance for the plurality of reference colors. The illuminance spectrum of reflected light is then determined according to these reflection coefficients Sb and Ss. Color data representing the colors of the print in a colorimetric system suitable for an output device are subsequently generated from the illuminance spectrum.

Method and apparatus for simulating color print

An N-dimensional correction space is constructed with weighting coefficients .xi. and .eta. that are used for determining reflection coefficients for an N-order target color, where the weighting coefficients .xi. and .eta. specify the lengths of the sides constituting the N-dimensional correction space, and where 2.sup.N reference colors are located at the corners of the N-dimensional correction space. The N-dimensional correction space is divided by N pieces of (N-1)-dimensional spaces that run through the target color, into 2.sup.N partial N-order correction spaces. The reflection coefficient for the target color is determined by multiplying a reference reflection coefficient with respect to each of the 2.sup.N reference colors by the volume of a partial N-dimensional correction space that is located at a diagonal position against a coordinate point of each reference color and summing up the results of multiplication for the 2.sup.N reference colors.

An illuminance spectrum I of reflected light from a color print of an arbitrary dot percent d is defined by a diffuse reflection coefficient Sb(d,.lambda.) and a specular reflection coefficient Ss(d,.lambda.). The diffuse reflection coefficient Sb(d,.lambda.) is determined by linear interpolation of a plurality of reference reflection coefficients Sb(d.sub.i,.lambda.) for a plurality of reference dot percents d.sub.i. The specular reflection coefficient Ss(d,.lambda.) is also determined by linear interpolation of a plurality of reference reflection coefficients Ss(d.sub.j,.lambda.) for a plurality of reference dot percents d.sub.j. The illuminance spectrum of reflected light is then determined according to these reflection coefficients Sb(d,.lambda.) and Ss(d,.lambda.). Color data representing the colors of the print in a calorimetric system suitable for an output device are subsequently generated from the illuminance spectrum.

There is provided a model where the illuminance of reflected light from the print is expressed with a linear combination of the illuminance of specular reflection light and that of internal reflection light. On the basis of the model, three methods are applicable to compute the colors of a print disposed in the three-dimensional space. In the first method, a specular reflection coefficient and an internal reflection coefficient, which are depending upon the wavelength, are interpolated by an angle of reflection .theta. and an angle of deviation .rho., and the illuminance spectrum of the reflected light is subsequently determined (step S2). Tristimulus values X, Y, and Z are then determined by integration of the illuminance spectrum according to the color matching functions (step S3). In the second method, the tristimulus values are determined for the specular reflection light, the internal reflection light, and the environmental light, respectively, and then interpolated by the reflection angle .theta. and the deviation angle .rho. (step S4). In the third method, the chromaticity coordinates are determined respectively for the specular reflection light, the internal reflection light, and the environmental light, and then interpolated by the reflection angle .theta. and the deviation angle .rho. (step S5).

The present invention provides an improved technique for extracting contours in an image without waiting for processing of all the scanning lines in the image. Run-data on two boundary scanning lines, each representing the boundary coordinates at which the image changes, are stored in a run-data buffer. A contour extraction unit compares two sets of the run-data with one another to extract segment vectors and detect a set of closed-loop vectors defining a contour of a image area. Three registers in a working buffer store specific data representing the relationship between a starting point and a terminal point of each vector sequence and are used in detecting closed-loop vectors. A vector data memory stores vector data including coordinate values of start and end points of closed-loop vectors. The contour extraction unit detects a vector sequence which has a starting point identical with a terminal point as a function of the data registered in the working buffer to identify the vector sequence as a closed-loop.

Method and apparatus for extracting a contour of an image

The present invention produces halftone dots which shows smaller fluctuations in size and shape irrespective of variation of the positional relation between the address of screen pattern data and the recording pixels. Displacement F1 through F4 are computed at vertices of a halftone dot region VP1 through VP4. Each of the vertices is shifted to a lattice point of the scanning coordinate systems, and the X-Y coordinates of each lattice point in the scanning coordinate systems are corrected accordingly. The displacement of an arbitrary lattice point A is interpolated from the displacement F1 through F4 on the basis of the distance between each vertex and the lattice point A. As a result, the positional relation between the address of the screen pattern and the position of the recording pixels is maintained constant in the vicinity of the vertices, and this reduces the fluctuations in size and shape of the halftone dots. The center of each halftone dot region can be shifted to a lattice point in the scanning coordinate systems.

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Tokyo, Japan

Nobuaki Usui