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Illumination selectable color profiling methods for improved color matching across multiple illuminants

IP.com Disclosure Number: IPCOM000199430D
Publication Date: 2010-Sep-02
Document File: 3 page(s) / 36K

Publishing Venue

The IP.com Prior Art Database

Abstract

This idea proposes methods of color profiling, in a color printing environment, with selectable illuminants. One method is to apply a chromatic adaptation transform to map D50 Profile Connection Space (PCS) values to L*a*b* values corresponding to the user-selected illuminant, followed by an illuminant-specific inverse printer model, to generate an ICC destination profile, which can be used with the standard source profile. Alternatively, if the source profile contains spectral characterization data, then a new source transform from device values to L*a*b* values can be calculated directly in the user-selected illuminant, and concatenating this with the illuminant-specific inverse printer model yields a device-link transform. If the illumination-specific Lookup Table's (LUT's) have to be created in the factory, and the illuminant is not selected at that time, it is proposed that LUT's are generated and stored for multiple standard or proprietary illuminants. When a new illuminant is selected later, a difference metric between the selected illuminant and the stored standard illuminants is calculated, and the nearest standard illuminant is chosen instead of rebuilding the LUT for the user-selected illuminant. As part of this idea, it is also proposed to store the illuminant specific LUTs in the document for later use in this manner.

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Illumination selectable color profiling methods for

improved color matching across multiple illuminants

This idea proposes methods of color profiling, in a color printing environment, with selectable illuminants. One method is to apply a chromatic adaptation transform to map D50 Profile Connection Space (PCS) values to L*a*b* values corresponding to the user-selected illuminant, followed by an illuminant-specific inverse printer model, to generate an ICC destination profile, which can be used with the standard source profile. Alternatively, if the source profile contains spectral characterization data, then a new source transform from device values to L*a*b* values can be calculated directly in the user-selected illuminant, and concatenating this with the illuminant-specific inverse printer model yields a device-link transform. If the illumination-specific Lookup Table’s (LUT’s) have to be created in the factory, and the illuminant is not selected at that time, it is proposed that LUT’s are generated and stored for multiple standard or proprietary illuminants. When a new illuminant is selected later, a difference metric between the selected illuminant and the stored standard illuminants is calculated, and the nearest standard illuminant is chosen instead of rebuilding the LUT for the user-selected illuminant. As part of this idea, it is also proposed to store the illuminant specific LUTs in the document for later use in this manner.

This idea proposes a method to extend the color profiling technology for use with a variety of illuminations. The user will be able to specify the illumination and create the L*a*b*/XYZ to CMYK lookup table specific to the user selected illumination and use it in the ICC framework for printing images. There are several new algorithm components (e.g., printer model, gamut mapping, construction methods of an ICC destination profile specific to an illuminant) being implemented to enable such an advanced feature. This invention also proposes to link an external illumination sensor to create the profile lookup table for an ambient illumination of choice.

Background:

Advanced profiling techniques described in Reference 1 assume a 2 degree observer and a D50 light source. When such profiles are used to match prints from multiple devices of same or differing technologies, the images may appear matched under the D50 illuminant, but may not match when viewed under a different illuminant.

Core algorithms (and patent coverage) exist for matching spot colors under specific illumination.  However, known approaches do not provide coverage for creating device link with source and destination profiles for illumination selectable rendering of images in an ICC framework.

Proposal:

This idea extends the spot color matching applications to provide illumination selectable rendering LUTs for a much broader printing or imaging display related applications. We show how a high accuracy source and destinationrendering LUTs are creat...