Guide to Color-Matching

Using Agfa Calibrator 4.x

with the KODAK APPROVALDigital Proofing System

DRAFT

June 21, 2001

First Draft

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Contents

1. Introduction........................................................................................................................3Purpose..................................................................................................................................3Compatibility..........................................................................................................................3General Notes.........................................................................................................................3About Workflow With this System............................................................................................4

2. Using Agfa Calibrator Software to Provide a Color Match............................................5Purpose..................................................................................................................................5Transfer Resource..................................................................................................................5Prerequisite Setup..................................................................................................................5How to: Set up a Calibration Curve.......................................................................................6How to: Enter Calibration Data..........................................................................................10How to: Display a Graph Showing Dot Gain Compensation................................................15How to: Edit Existing Calibration Data................................................................................16

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1. Introduction

PurposeThis document is intended as a reference guide to the overall procedures for performing a color match when using Agfa Calibrator 4.x software with KODAK APPROVAL Classic and KODAK APPROVAL XP/XP4 Digital Proofing Systems. The intent of this Guide is to supplement the standard documentation that is available with Approval systems and with Agfa Calibrator software. This standard documentation includes the following:

Kodak Approval XP, User’s Guide.

Apogee PS Companion User Guide. This user manual contains a section on Agfa Calibrator 4.x.

The information in this Guide will assist a Kodak Application Specialist in performing standard color-matching procedures at a site using a Agfa Apogee RIP with an Approval system. This Guide makes two key assumptions:

(1) The Application Specialist has had some experience in performing color matching when using RIP utilities from other sources.

(2) A customer or software support specialist who is knowledgeable Agfa Apogee software will be working on-site with the Kodak Application Specialist when performing color matching procedures.

It must be emphasized that this Guide is not intended to fully train the Kodak Application Specialist on all aspects of the Agfa Calibrator system. The goal of this document is to familiarize Kodak personnel with the overall arrangement and workflow aspects of the Agfa Calibrator software, so that the Application Specialist can, with a reasonable amount of effort, work efficiently with on-site staff to obtain a color match.

CompatibilityThe information in this Guide is compatible with Agfa Calibrator software, version 4.x or later. This software is compatible with the AIT (Approval Interface Toolkit) interface to Kodak Approval and Approval/XP systems.

General Notes(1) There are many options not discussed in the procedures that follow. These procedures are intended to show the most straightforward paths through the system for the purpose of generating digital proofs and obtaining a color match. Consult the Agfa Calibrator documentation for more complete information on the procedures described here and for information on options and capabilities not discussed in this Guide.

(2) Menu selections are indicated in the following general format:

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Menu selection --> Command

(3) The operator interface is fairly intuitive with respect to icons and window interaction. There are often multiple methods available for initiating different operations (for example, double-clicking the mouse or entering a menu command).

About Workflow With this SystemWorkflow organization and execution follow the pattern used by Agfa Calibrator software. The next section describes only those eements of the Agfa Calibrator workflow that are useful to the Application Specialist for obtaining a color match.

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2. Using Agfa Calibrator Software to Provide a Color Match

PurposeThe background and procedural information in this section is intended to provide a starting point for an Application Specialist assigned with the task of preparing a color match. For this reason, the information in this section is limited to a subset of the system and its operator interface windows.

The Agfa RIP accepts a 1-bit TIFF file as input and processes the file as a set of color separations. Each color separation is processed using a calibration curve set up in Calibrator software.

The calibration curve set up in Calibrator software accepts benchmark (Measured) and target (Wanted) dot gain values, expressed as dot percentages. The Calibrator software, given this data, then builds a curve that allows dot reproduction by the proofing system to emulate the performance of a target device.

Agfa Calibrator 4.x software executes on a Mac client.

The procedures that follow assume that a PPD file has been generated for the output device.

Transfer ResourceThe Transfer Resource is a calibration file used by the Agfa RIP software. A Transfer Resource incorporates dot gain values set up for each color separation and allows these values to be applied to each print job.

Prerequisite SetupIn order to use Calibrator 4.x software with the proofing system, it is necessary that PPD files first be created and stored for the proofing device. A separate AgfaSet utility, described in chapter 2 of the Apogee PS Companion User Guide, enables creation of PPDs for use with any compatible output device.

Before initiating Agfa Calibrator 4.x software, use Chooser on the Mac desktop to select the appropriate printer settings for Agfa workflow.

For reading and entry of calibration values, prepare benchmark and target proofs in readiness for the following procedure.

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How to: Set up a Calibration CurveStart up the Calibrator software application from the client desktop. Use the following sequence:

1. Click on the Calibrator 4.x icon that displays.

In response, the Calibration Setup window of Figure 2-1 appears.

Figure 2-1. Calibration Setup Window

2. Make the appropriate entry in the Device: field. Specify Device: Color Separations.

3. Click Load PPD…

In response, the system displays a PPD selection window, as shown in Figure 2-2.

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Figure 2-2. PPD Selection Window

4. Select the desired PPD file and click Open.

As an optional step, enable one or both of the Select PPD file options displayed:

Remember Folder Enable to use the current folder as the default address for searching for PPD files.

For use with Halftone Linked Transfer Resources

Enables saving the calibration curve as a Halftone Linked Transfer Resource.

The PPD selection determines what options will be available for dot shape and other screening characteristics.

In response, the revised Calibration Setup window of Figure 2-3 displays.

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Figure 2-3. Revised Calibration Setup Window

5. Make appropriate entries in the revised Calibration setup window, as listed below.

Color: Select appropriate color for separation.

Frequency: Specify appropriate frequency. Must match a corresponding value available from the PPD.

Angle: Specify appropriate screen angle. Must match corresponding value available from the PPD.

Resolution: Specify appropriate resolution value. Must match corresponding value available from the PPD.

Dot Shape: Select appropriate dot shape. The listing of dot shapes available from the pull-down menu is taken from the PPD selected in step 4.

5. In the Type: field, select the appropriate screening and resolution entry from the pull-down menu.

6. Click OK.

In response, the system displays an array of calibration values for the first separation, as shown in Figure 2-4.

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Figure 2 4. Calibration Values Entry Window

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How to: Enter Calibration DataThe calibration values entry window of Figure 2-4 accepts variable entries in each of its three major columns:

Stimuli – the reference or nominal values for different dot percentages.

Measured – the benchmark values for the proofing system. Entry of Measured values allows Calibrator 4.x software to linearize the response of the proofing system, so that a 50% input dot value provides a 50% output dot, for example.

Wanted – the target values for the imaging system to be matched. Entry of Wanted values allows the response curve of the proofing device to match the response of a printing press, platemaker, or other imaging device.

The Stimuli column lists each of 21 percentage values that correspond to Measured and Wanted values. By default, these nominal dot percentages are listed at 5% intervals as shown in Figure 2-4. However, other groupings are possible, depending on requirements for dot gain matching at the site. For example, it may be desirable to adjust values in highlight, shadow, or midtone regions for a fine-tuned calibration curve. The procedures given below describe how to redistribute the value assignments shown in this table.

Follow these steps to enter and apply calibration values using the window of Figure 2-4:

1. Make any necessary Values selection, enabling or disabling the following options:

Smooth – applies a smoothing algorithm to the final calibration curve.

Negative – allows entry of values for a negative output. In such a case, a low Stimulus value maps to a high Measured value. (Do not use this setting with a densitometer setting that converts measurements from a negative image to a positive value.)

2. Select Units for each column as follows:

Dot % -- (Default) accepts values entered as standard dot percentages.

Density – accepts values entered as densities.

3. (Optional.) If necessary, adjust the Stimuli value groupings to suit requirements for this setup. To do this, use the pull-down menu selections available within the Stimuli column. These selections are as follows:

Spread Full Range – Applies the adjustment selection from the submenu that follows to the full range of values, from 0 to 100%, as specified:

Linear. Default 5% intervals used.

More Values in Highlights. Increases the proportional number of rows among the highlight values.

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More Values in Midtones. Increases the proportional number of rows among the midtone values.

More Values in Shadows. Increases the proportional number of rows among the shadow values.

Spread Selection - Applies the adjustment selection from the submenu that follows to a highlighted range of values from the calibration values entry window, as shown in Figure 2-5:

Linear. Default 5% intervals used over the selected interval.

More Values in Highlights. Increases the proportional number of rows among the highlight values over the selected interval.

More Values in Midtones. Increases the proportional number of rows among the midtone values over the selected interval.

More Values in Shadows. Increases the proportional number of rows among the shadow values over the selected interval.

4. Enter the Measured values. To do this:

4a. Clear the Measured column to facilitate entry of benchmark values. To do this, select Clear Array from the pull-down menu accessible at the top of the Measured column.

4b. Enter Measured values obtained from a benchmark proof.

5. Enter the Wanted values. To do this:

5a. Clear the Wanted column to facilitate entry of target values. To do this, select Clear Array from the pull-down menu accessible at the top of the Wanted column.

5b. Enter Wanted values obtained from a target proof.

6. Click Apply.

The system responds by displaying the Apply Setup window of Figure 2-6.

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Figure 2-5. Value Grouping for a Selected Range

Figure 2-6. Apply Setup Window

7. From the pull-down menu, specify Transfer Resource. (This selection appears as the default.)

8. Click OK.

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The system applies the dot gain setup to linearized curves. The window of Figure 2-7 prompts for a transfer resource name.

Figure 2-7. Transfer Resource Naming Prompt

9. Enter a new Transfer Resource name and click OK.

Enter a descriptive name for the Transfer Resource, with identifying calibration information, as is shown in the example of Figure 2-7. The Transfer Resource name is limited to 31 characters. No spaces are permitted.

When calibrating for the first color in a series, define and name a new Transfer Resource. Then, store calibration data for subsequent colors under that same Transfer Resource name. For the specific color, specify the correct Transfer Function in the window that displays.

The system responds with the File Save window of Figure 2-8.

10. Enter a suitable file name and click Save.

11. Repeat steps 5 and 6 from the preceding section and steps 1 through 10 of this section for each color to be used on the proof.

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Figure 2-8. File Save Window

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How to: Display a Graph Showing Dot Gain CompensationOnce calibration values have been saved, view any calibration curve using the following main menu command, ending with a color specification, for example:

Calibrator Graph Black

In response, the system displays a calibration curve, as in the example of Figure 2-9.

Figure 2-9. Calibration Curve

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How to: Edit Existing Calibration DataTo edit an existing color calibration, use the following steps:

1. Enter the following command sequence from the main menu:

File Open

In response, the file selection window of Figure 2-10 displays.

Figure 2-10. File Selection Window for Color Calibration

2. Select the color calibration file to edit and click Open.

The system displays a calibration values entry window, as was shown in Figure 2-4.

3. Edit the necessary values, then click Apply.

In response, the system displays an Apply Setup window, as was shown in Figure 2-6.

4. Specify Transfer Resource and click OK.

In response, the system prompts for Transfer Resource information with the window of Figure 2-11.

5. Complete the window displayed for the following fields:

Apply to: Existing Transfer Resource

Transfer Function: (specify appropriate color).

Then click OK.

In response, the selection window of Figure 2-12 displays.

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Figure 2-11. Prompt for Editing Existing Transfer Resource

6. Specify the appropriate transfer resource file. To do this, highlight the file name with a mouse click, then click Open.

The Transfer Resource file is then updated with the new changes.

Figure 2-12. Selection Window for Transfer Resource File

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