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Method for selecting a color transformation

A technology for conversion into and destination, applied in the direction of image communication, electrical components, etc., can solve the problem that the sum of colorants and black colorants cannot provide useful and reliable indicators

Active Publication Date: 2009-12-02
AGFA OFFSET BV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

In this case, neither the maximum value of the colorant sum nor the maximum amount of black colorant in the separation provides a useful and reliable indicator of which destination profile was used

Method used

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  • Method for selecting a color transformation
  • Method for selecting a color transformation
  • Method for selecting a color transformation

Examples

Experimental program
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no. 1 example

[0178] The first but not preferred embodiment works as follows, and by Figure 5 to explain.

[0179] This first embodiment assumes that the destination profile also includes a forward lookup table (which is not always the case).

[0180] In a first step (500), a pixel of a destination image having a destination vector (c, m, y, k) is selected.

[0181] In a second step (510), the destination vector (c, m, y, k) is converted into a source vector (L, a, b) using a forward lookup table of candidate destination profiles. This is achieved by employing one of the known interpolation techniques such as N-dimensional interpolation or tetrahedral interpolation.

[0182] In the same second step (510), the source vector (L, a, b) is converted back to an approximate destination vector (c', m', y', k'). Similarly this is achieved by employing one of the known interpolation techniques such as three-dimensional interpolation or tetrahedral interpolation.

[0183] Next calculate (530) the...

no. 2 example

[0217] Second Embodiment - Basic Principles

[0218] The second embodiment overcomes the limitations of the first embodiment.

[0219] In the previous example, first use forward lookup table A source vector (L, a, b) corresponding to a destination vector (c, m, y, k) in the destination image is obtained. This source vector is then used to obtain an approximate destination vector (c', m', y', k') using a reverse lookup table.

[0220] In the current and preferred embodiment, only use reverse lookup table . This may not be easy to understand at first glance, but it will become clear after reading the rest of this text. As for the rest, the second and preferred embodiment uses the same steps as the first embodiment, including optimization.

[0221] Equation 1, derived in an inverse lookup table for a particular tetrahedral cell, predicts a 4D destination vector (c, m, y, k) from a 3D source vector (L, a, b).

[0222] From a geometric point of view, this transformation l...

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Abstract

An output color profile, such as an ICC output profile, contains a look-up table to separate the color of a pixel, for example a CIELAB color, into a set of colorant values, for example CMYK colorants. In practice, most CMYK images have been separated using one of a limited set of standardized output profiles. The invention deals with the problem of guessing which one of these standardized output profiles has been used to separate a specific image. For this purpose the CMYK values of the image are analyzed. The analysis involves calculating a distance in the CMYK space between the CMYK values of an image, and the CMYK values produced by different output profiles. A profile is selected based on these distances, for example by selecting the profile yielding the shortest distance.

Description

technical field [0001] The invention relates to the field of color image reproduction. More specifically, the present invention relates to the field of color management systems for obtaining faithful color reproduction of color images. Even more particularly, the present invention relates to methods for determining which output color profile was used to separate an image into colorant values. Background technique [0002] background overview [0003] The faithful reproduction of color images on color printing devices relies on a color management system. Such a system converts the color values ​​in the original file to the colorant values ​​of the printing system so that the colors in the original file are faithfully rendered. [0004] Most commercial color management systems are based on the International Color Council (ICC) specification for representing color transformations. The International Color Council has a website at http: / / www.color.org. [0005] According to...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H04N1/60
CPCH04N1/6052H04N1/6011
Inventor M·马伊P·德拉巴斯蒂塔
Owner AGFA OFFSET BV
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