Seiko Epson Corporation

Tsung-Nan Lin

Joseph S Shu

Anoop Kumar Bhattacharjya

Hakan Ancin

Jerzy Wieslaw Swic

Jau-Yuen Chen

A technique is provided that identifies screen and non-screen regions of a projected or displayed image to smooth and selectively remove moir&#xe9; from the screen regions while maintaining sharpness in the non-screen regions. Each pixel in the image is classified as a screen or non-screen pixel and then pixels in a predetermined surrounding area of each pixel are examined to check the classification of that pixel. A low pass filter is applied to pixels in the image, such that, when the low pass filter is applied, a center of the low pass filter is selectively shifted relative to a current pixel based on the examination.

Image artifact removal technique for LCP

When clustered-dot dithering is employed in laser printers a banding effect sometimes results from the interaction of the dither matrix with non-uniform line spacing in the printer. We have found that we can lessen the effect of this interaction if we change the dither matrix as it moves over the image. We do this by modulating the dither matrix (halftone cell) as a function of the spatial position of the sub-area in the image. Halftone cells can be formed in a variety of patterns (e.g. vertical, horizontal, etc.) but generally their threshold values grow from a minimum value to a maximum value. Our process is to modulate the halftone cell according to a function: f (s, h) where s is the spatial position of the sub-area of the image and h is the halftone cell. We modulate the cell by altering the relative positions of the threshold values in the cell as we move the cell over the image. This effectively breaks up the bands of clusters of one size or another and provides a visually uniform image even in lighter tones.

Smoothness enhancement in laser printing through periodic modulation of halftone cell

An apparatus and method for improving a color space transformation between an input device such as a scanner and an output device such as a printer. The color space transformation includes a first three-dimensional look up table that receives color information from the input device and transforms colors specified in an input device color space into colors in a device-independent color space, and a second three-dimensional look up table that receives colors from the first three-dimensional look up table and transforms colors specified in a device-independent color space into colors in an output device color space. The method includes inputting sample images with the input device and outputting those sample images with the output device, identifying areas in the sample images output by the output device where contouring appears, forming a list of colors corresponding to the identified areas, identifying nodes in the second three-dimensional look up table encompassing the list of colors, and smoothing the set of nodes.

Color table manipulations for contour reduction

A method and apparatus for improving color matching between original color images and reproductions thereof. Incorporated into the improved color matching technique is an improved out-of-gamut mapping strategy which does not affect in-gamut colors but which ensures that colors outside of the input device gamut will be mapped to the boundary of the output device gamut while preserving hue and minimizing the combined chrominance-luminance error.

Out-of-gamut color mapping strategy

A technique for calibrating non-reference printers to a reference printer in a network system by determining a set of four 1-D look-up tables for each non-reference printer. Each set of four 1-D look-up tables is constructed from a corresponding set of transfer functions, where each transfer function in a given set is a composite of a 1-D characteristic function for a particular primary color of the reference printer and a 1-D inverse characteristic function for that particular primary color of the corresponding non-reference printer. The characteristic functions are determined by performing a specific color space transformation analysis on each non-reference printer and on the reference printer.

Self-calibration of network copier system

A color image reproduction system achieves higher-quality color reproduction by improving the utilization of colors within the gamut of an output device that are not in the gamut of an input device. This is accomplished by a device-dependent compensation transformation that maps a second set of colors in both the gamut of an input device and the gamut of the output device into a first set of colors in the gamut of the output device but not in the gamut of the input device. The compensation transformation may be derived in a number of ways that entail identifying the first and second sets of colors and then determining one or more scaling factors that map the second set of colors into a union of the first and second sets of colors.

Color image reproduction with accurate inside-gamut colors and enhanced outside-gamut colors

In an image reproduction system, an image processor analyzes a hierarchy of image representations of different resolutions to detect edges. In regions having edges that are detected in all hierarchical representations, little or no filtering is applied to the image. In regions having no edges or edges that are detected in only the highest-resolution representation, greater amounts of filtering are applied to the image. In regions having edges detected in two or more but not all hierarchical representations, an intermediate amount of filtering is applied to the image. In preferred embodiments, two-dimensional averaging filters of varying size are applied to the image. The size of the averaging filter is selected according to the number of hierarchical representations in which an edge is detected.

Reduction of moir&eacute; in screened images using hierarchical edge detection and adaptive-length averaging filters

The present invention is directed to an apparatus and a method to improve color matching between original color images and reproductions of those images. The present invention is implemented by a look-up table that maps colors from a first color space to a second color space for a color image reproduction system comprising an input device and an output device is achieved by identifying a region of the second color space in which the accuracy of the transformation is to be improved, obtaining a medium conveying a selected color within the region of second color space, scanning the medium with the input device to obtain first values representing the selected color in the first color space, applying the transformation to map the first values to second values in the second color space and determining a transformation error for the map, and modifying one or more entries in the look-up table to effect a change in the transformation so as to reduce the transformation error.

Color matching accuracy inside and outside the gamut

A recalibration transformation is derived for a color image reproduction system having an input device and an output device by obtaining a medium conveying a selected color within a current gamut of the output device represented by first values in a first color space, scanning the medium with the input device to obtain second values representing the selected color in a second color space, applying a calibration transformation to map the second values to third values in the first color space, deriving an error transformation that maps from the first values to the third values, and deriving the recalibration transformation from an inverse of the error transformation that maps from the third values to the first values.

Self-calibration for color image reproduction system

The present invention is directed to a method and apparatus for improving color matching between original color images and reproductions thereof. In the present invention, color space transformations are derived for a color image reproduction system comprising an input device and an output device by obtaining a first transformation for the input device that maps from colors within an input-device-dependent color space to colors within a first device-independent color space, and obtaining a normalization transformation that normalizes information obtained from the first transformation with respect to a white point in a second device-independent color space.

Device-independent and medium-independent color matching between an input device and an output device

The present invention is directed to an apparatus and a method to improve color matching between original color images and reproductions of those images. The present invention comprises an input device and an output device by obtaining a first transformation that maps points representing colors within a first output-device-gamut from a device-dependent color space to points in a device-independent color space, obtaining a second transformation that maps points representing colors within a second output-device-gamut from the device-dependent color space to points in the device-independent color space, and deriving the color space transformation such that it maps a respective point from the device-dependent color space to a corresponding point in the device-independent color space according to whether the respective point is within either or both of the first and second output-device gamuts.

Scanner calibration technique to overcome tone inversion

The gray shade rendering capability of a display device having a frame rate of q frames per display cycle is enhanced by comparing an intensity value representing a gray shade of a current pixel with a respective dither matrix threshold value and providing a pixel on/off signal, storing a plurality of quantization values ranging from 1 to q in a quantization table, outputting p quantization values from the quantization table as active quantization values in accordance with a quantized pixel value p, shifting the quantization values in the table in response to a frame signal, comparing a quantized dither matrix threshold value to the active quantization values and producing an active quantized threshold signal, producing a pixel out signal in response to the pixel on/off signal and the active quantized threshold signal, and in response to the pixel out signal displaying the current pixel with an average gray value of p/q through a display period of q frames.

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San Jose, CA, United States of America

Tsung-Nan Lin