Abstract
A method is provided for printing color images using a color workflow. This workflow results in equal output colors from two print systems. For a first print system an existing color output profile for converting colors is used. An actual output color profile for the first print system is obtained from color measurement data that relate device colorant coordinates of the first print system to device independent color data. The existing output color profile does not correspond to the color measurement data. For a second print system, an additional output color profile is obtained from color measurement data. The color workflow that is applied in the second print system for converting colors of an input image is made by combining the existing output color profile, the actual output color profile and the additional color output profile, wherein the actual output color profile is applied in an inverse direction (A2B).
Claims
1. A method for printing color images using a color workflow that results in equal colors from an existing print system and an additional print system, the existing print system applying an existing output color profile for converting colors of an input image, the additional print system applying said color workflow for converting colors of an input image, the method comprising the steps of: a) obtaining an additional output color profile for the additional print system from color measurement data that relate device colorant coordinates of the additional print system to device independent color data; b) obtaining an actual output color profile for the existing print system from color measurement data that relate device colorant coordinates of the existing print system to device independent color data; c) obtaining the existing output color profile; d) combining the existing output color profile, the actual output color profile and the additional color output profile in the color workflow, and e) converting the colors of an input image according to the color workflow and printing the converted image using the additional print system, wherein the existing output color profile does not correspond to the color measurement data in step b) and the actual output color profile is applied in an inverse direction (A2B) in the step of combining output color profiles.
2. The method according to claim 1, wherein the color workflow is stored as an output color profile for the additional print system.
3. The method according to claim 1, wherein the actual output color profile and the additional output color profile are combined in a device link profile.
4. The method according to claim 1, wherein the color workflow is combined with an input color profile to a device link profile for the additional print system.
5. The method according to claim 4, wherein a number of color profiles of the color workflow are combined in a device link profile.
6. The method according to claim 1, wherein the color workflow is associated with a medium that is applicable in the additional print system, such that the color workflow is applied when the medium is selected as output medium for an input image to be printed.
7. The method according to claim 1, wherein an output table of the existing output color profile and an input table of the actual output color profile are stored as an extraordinary color profile, wherein the two tables are not each others inverse.
8. A print system for printing color images using a color workflow for converting colors of an input image resulting in equal colors as obtained from an existing print system, the existing print system applying an existing color output profile for converting colors of an input image, the print system being configured to combine the existing output color profile, an actual output color profile, that relates device colorant coordinates of the existing print system to device independent color data, and an additional output color profile, that relates device colorant coordinates of the print system to device independent color data, in the color workflow, wherein the existing output color profile does not correspond to the color measurement data of the existing print system and the actual output color profile is applied in an inverse direction (A2B).
9. The print system according to claim 8, wherein a user interface is configured to enable a selection of an existing color output profile, an actual output color profile and an additional output color profile that are combined in the color workflow.
10. The print system according to claim 8, wherein the color workflow is associated with a medium that is applicable in the print system, such that the color workflow is applied when the medium is selected as output medium for an input image to be printed.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
[0017] FIG. 1 shows a number of known color workflows for printing data;
[0018] FIG. 2 shows a color workflow according to the invented method;
[0019] FIG. 3 is a user interface for defining a color workflow, and
[0020] FIG. 4 shows the individual steps for obtaining an invented color workflow.
DETAILED DESCRIPTION OF EMBODIMENTS
[0021] The present invention will now be described with reference to the accompanying drawings, wherein the same or similar elements are identified with the same reference numeral.
[0022] In FIG. 1, an input image 1 comprising color information is scheduled to be printed on print engine 2. An image in the present context means anything that can be displayed, including text and graphics. Three possible, known workflows are available for converting the color information into printer coordinates. A selection of a workflow may be made automatically in the digital front end, where the input data are rendered, but, alternatively, a user may define a preferred workflow, if it is compatible with the input data. The input data may comprise an input color profile for converting the input image data into a Profile Connecting Space (PCS), such as the CIE-Lab color space. Often, the input data refer to standard printing conditions, such as SWOP or FOGRA39 or a standard color space, such as sRGB. In case no input profile is included in the input data, an input color profile is either available in the digital front end or may be found on the internet. Workflow A refers to a case wherein the color input data is directly converted by a device link profile 3, without using a PCS. Workflow B is the standard ICC workflow that comprises an input color profile 4 and an output color profile 5 that both may comprise a relation between a specific device or a standard color device and a PCS. The A2B-table of the input profile is joined with the B2A-table of the output profile to obtain a color conversion that is compatible with the color specifications of the print engine 2. Workflow C is a simulation color workflow that is used to convert the colors of the input image in such a way that the colors in the output of the print engine 2 do not extend beyond a gamut of a simulated device. In this simulated device, the simulation profile 6 is used as an output profile. It is assumed in this workflow that the simulated device accurately, i.e. according to color measurements, renders the colors of the simulation profile. In the simulation workflow C, the simulation profile is applied twice, once to convert a PCS color to the simulated device coordinates, and a second time to convert the simulated device coordinates back to the PCS. In practice, the accuracy assumption does not always hold. Print systems apply color profiles that are colorimetrically not accurate, but it is still required to match an additional printer to an existing print system, while maintaining the inaccurate profile.
[0023] FIG. 2 shows a workflow that may be used in such a case. The print engine 2 of FIG. 1 is considered to be part of an existing print system for which the workflows and profiles of FIG. 1 are maintained. An input image 1 is printed on an additional printer 10. First, the input data are converted by the input and output profiles 4 and 5 in the same way as in workflow B in FIG. 1. If a device link profile is available, it is also possible to replace the profiles 4 and 5 by the device link profile, as in workflow A in FIG. 1. An actual profile 11, that accurately describes the color behaviour of the existing print engine 2, is inserted to convert a color as defined in print engine 2 coordinates to the PCS. This actual profile is a new profile obtained from color measurements on print engine 2. It is therefore an output color profile that is applied in the inverse direction. Once a color is in the PCS, it may be converted to coordinates of an additional printer by an additional output profile 12, that is obtained from color measurements on the additional printer 10 in the usual way. Thus, the output colors of additional printer 10 are similar to the colors of print engine 2.
[0024] FIG. 3 shows a user interface 20 for defining the color matching workflow. For an existing printer, the existing printer parameter set 21 is selected. This set comprises the complete definition of parameters that are used in the color workflow of the existing printer, such as an input and output color profile (or a device link profile), the applied rendering intent, the black point compensation method, the pure color preservation, etc. Thus, in the color matching workflow, an exact copy of the color workflow for the existing engine can be applied. Also, an actual profile 22, reflecting an actual relation between the existing printer coordinates and the PCS, is inserted and a color output profile 23 as determined from measurements on the additional printer 10. The rendering intent for using the actual profile 22 and color output profile 23 is preferably the absolute rendering intent, or, alternatively, the relative rendering intent without black point compensation, in order to convert the colors as directly as possible. However, in this embodiment, this parameter is not selectable, but fixed, but alternatively it is selectable. Furthermore, in box 24, this color workflow may be associated with a medium from the medium list of additional printer 10, such that this workflow is automatically selected when a user selects this medium to print the input image.
[0025] FIG. 4 shows the individual steps that are taken to obtain the required profile data to apply the color workflow as shown in FIG. 2. In step S1, a test chart is printed on an existing print engine, such as print engine 2 in FIG. 1. An actual color profile 11 is determined in step S2. In step S3, a similar test chart is printed on the new, additional printer 10 in FIG. 2, for which an output color profile 12 is determined in step S4. Subsequently, in step S5, the existing output profile 5 as used for the existing print engine 2 is obtained. Then, in step S6, these profiles are concatenated as indicated in FIG. 2. It is noted, that several commercial software programs, such as X-rite i1 Profiler, exist for making the necessary calculations, both for making color profiles from test chart measurements and for concatenating various profiles. Also, Color Management Modules (CMM) by Adobe and Microsoft, are capable of assembling various color profiles in a color workflow. In the present embodiment, non-commercial, proprietary software has been used to make the various interpolations and interpretations that are necessary to obtain the profiles, but this is well known in the art of color management.
[0026] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
