Abstract: A method for compressing a first bit digital input representative of first pixel data into a second bit digital output representative of second pixel data, the method comprises the steps of defining a logarithmic function for converting the first bit digital input into the second bit digital output; replacing a portion of the logarithmic function with a polynomial function; and compressing the first bit digital input into the second bit digital output by utilizing the logarithmic and polynomial function.

Abstract: Multi-channel color image signals from a digital camera having multi-channel image sensors are corrected to account for variations in scene illuminant. This is accomplished by determining the scene illuminant and determining an optimum color-correction transformation in response to the scene illuminant which transform minimizes color errors between an original scene and a reproduced image by adjusting three or more parameters.

Abstract: A multicolor dye-donor element for thermal dye transfer capable of producing improved color gamut comprising a support having thereon a set of sequential repeating dye patches of yellow, magenta and cyan image dyes dispersed in a polymeric binder, the element also having at least one additional dye patch comprising a dye dispersed in a polymeric binder, the dye of each such additional dye patch which, when transferred to a dye image-receiving layer before or after transfer of the original yellow, magenta and cyan image dyes, has a hue measured at its maximum density which is outside the color gamut defined by the hues of the original transferred yellow, magenta and cyan image dyes by more than 5 CIELAB .DELTA.E.sub.c units.

Abstract: Sensitometric information is stored with a consumable print medium having a predetermined sensitometry by compressing the sensitometric information as a set of spline coefficients for use with a printer adapted to decode the set of spline coefficients to construct a sensitometric curve. A set of spline coefficients is generated, spline coefficients are encoded, and the encoded spline coefficients are stored in a manner which is accessible to a printing device adapted to make use of the media sensitometry data for purposes of device calibration. The coefficient-generating step comprises fitting a spline curve to the sensitometry data. The spline curve may be monotonic cubic. The encoding step may include encoding a difference signal representing a difference between input values for a set of sequential spline knots.

Abstract: An error diffusion method suitable for producing an output image from an input image having a set of digitized continuous-tone pixels is disclosed. The method includes the steps of computing an image activity signal; computing a set of activity weights from the image activity signal; computing a filtered input value for a digitized continuous-tone input pixel responsive to the activity weights and computing a filtered output value responsive to the activity weights for each of the possible output levels. The method further includes selecting the output level in response to the filtered input value and the filtered output value for each of the possible output levels according to an error criterion; determining an error signal between the filtered input value and the filtered output value for the selected output level; and weighting the error signal and adjusting the filtered input values for nearby pixels which have not yet been processed.

Abstract: A method for compressing a first bit digital input representative of first pixel data into a second bit digital output representative of second pixel data, the method comprises the steps of defining a logarithmic function for converting the first bit digital input into the second bit digital output; replacing a portion of the logarithmic function with a polynomial function; and compressing the first bit digital input into the second bit digital output by utilizing the logarithmic and polynomial function.

Abstract: A method for transforming input color values of a digital image to produce suitable output color values for use by a particular device is disclosed. In this method a plurality of color transforms are stored, each such transform responds to input color values of a digital image and produces output color values which can be used by the particular device. In the method an intermediate transform which is user desirable for transforming the input color values is formed by interpolating between the plurality of transforms.

Abstract: Method and apparatus for generating a halftone image for a multi-level output device employing a dither matrix generated by minimizing a visual cost function. The dither matrix is addressed by the least significant bits of a pixel address and the value supplied by the dither matrix is added to the pixel value. The resulting sum is quantized in a quantizer to produce the multi-level halftone value.

Abstract: This invention provides a method for transforming an input color space to an output color space where each of a plurality of specified colors and/or color regions are constrained to be transformed by any one of a plurality of explicitly specified color calibration or color enhancement strategies. The method involves a two step process: 1) constraints are applied to some subset of the points in the input color space explicitly specifying the transform into the output color space; 2) the reminder of the points are then transformed by a mapping strategy which preserves color continuity. The mapping strategy used in the preferred embodiment is based on a computer graphics geometric morphing technique. In the preferred embodiment, multi-dimensional look-up tables are used to implement the color transformation.

Abstract: An improved error diffusion method for producing an output image from an input image having a set of digitized continuous-tone pixels is disclosed. The method includes computing a visually perceived input value for a digitized continuous-tone input pixel and computing a visually perceived output value for each of the possible output levels. The method further includes selecting the output level in response to the visually perceived input values and the visually perceived output value for each of the possible output levels according to an error criterion; determining an error signal between the visually perceived input value and the visually perceived output value for the selected output level; and weighting the error signal and adjusting the computed visually perceived input values for nearby pixels which have not been processed.

Abstract: A method of calibrating a four color printer capable of printing three colors and black, includes the steps of: forming a minimum black data structure representing a minimum black strategy; forming a maximum black data structure representing a maximum black strategy; for each printable black level, forming a fixed black data structure; and for a specific output color value, finding the minimum and maximum black levels using the minimum and maximum black data structures, determining a desired black level between the minimum and maximum black levels according to a defined black strategy, and determining the three printing color levels from the fixed black data structure corresponding to the desired black level.

Abstract: This invention provides a method for mapping an input color space to an output color space in such a way that the color reproduction characteristics of the saturated colors can be adjusted in a custom manner, while maintaining the desired tone reproduction on the neutral axis. This is accomplished by defining independently a tone transformation and a transformation for a plurality of highly saturated colors. A transformation is formed for the remaining color values having the specified transforms for the neutral and saturated colors as boundary values. In the preferred embodiment multi-dimensional look-up tables are used to implement the transform.

Abstract: This invention minimizes the color errors associated with performing conversion and/or correction of color digital image data using multi-dimensional look-up tables of a limited size. By distributing the errors across the color gamut it is possible to reduce the average color error as well as the maximum color errors associated with linear or conventional linear or nonlinear, e.g. cube-root or logarithmic, remapping schemes. The resulting advantage will be color images with greatly reduced artifacts.

Abstract: This invention minimizes the visibility of quantization artifacts associated with multi-dimensional color-calibration look-up tables of a limited size. Such artifacts occur when it is not practical to use interpolation methods to approximate color values which are intermediate to the color values stored in the look-up table. In such cases the input color signals are simply quantized for the purpose of addressing the look-up table. This invention works by applying local mean preserving spatial modulation to the input color image values prior to the quantization step. As with multi-level halftoning techniques, the result is that the appearance of intermediate color values is created because the observer will spatially average the output color values.

Abstract: In the present invention each input pixel value is compared against a randomly selected threshold value to provide an output pixel having a value indicative of which of the values is greater. The threshold value is selected from one of a plurality of threshold matrices, each having a predetermined number of threshold values that are arranged in a pattern with the values for a base matrix being increased by an increment for each succeeding one of the plurality of threshold matrices. The selection of the one threshold matrix is made by means of a pseudo-random number generator.