Color Matching For HP Digital Presses How-to Guide Copyright © 2009 by Hewlett-Packard Company All Rights Reserved. Reproduction, adaptation, or translation without prior written permission is prohibited, except as allowed under the copyright laws. The information furnished in this document is for informational purposes only, is subject to change without notice, and should not be construed as a commitment by HP. HP assumes no responsibility or liability for any errors or inaccuracies that may appear in this document. The varnishes and coatings discussed and/or recommended in this document are sold and distributed by third-party manufacturers and should be used solely in accordance with their instructions. These products are not manufactured or sold by HP and nothing contained herein should be construed as constituting a representation or warranty of any kind by HP. Except as permitted by HP, nothing herein may be copied, reproduced or distributed in any form or by any medium without the express, written permission of HP. HP, HP Indigo Press, and HP ElectroInk are trademarks or registered trademarks of HP. All other products or name brands are trademarks of their respective holders.

Part Number: CA394-03840 4AA4-1353ENUC June, 2009 Contents

Color Matching Using HP Indigo presses Who can benefit from reading this document? ...... 2 Overview ...... 2 HP Indigo Press - related Color Matching Tools ...... 3 Color Profiling ...... 6 Evaluating Color Match ...... 6 Best Practice ...... 7 Calibrating for best color match Pre-calibration...... 8 Substrate definition ...... 8 Achieving the best color matching between HP Indigo presses ...... 10 Color Control Procedure...... 12 Calibration guidelines ...... 13 Achieving the best color matching between sites Color matching procedure for multiple sites ...... 15 Determining substrate type Exceptions and troubleshooting ...... 18

1 Color Matching Using HP Indigo presses

Who can benefit from reading this document?

z HP Indigo press customer engineers z HP Indigo press application engineers z Customer site managers

Overview

Today’s modern printing industry requires the ability to produce identical on different presses and at different sites. This document provides information on how to achieve the best color match possible for HP Indigo presses.

Most of the color matching issues seen in the field are due to either press calibration issues or to the use of a different RIP's and different color profiles on the presses.

As more customers try to match their different presses by manipulating color profiles, the issue of color match between presses becomes critical. Customers use different color profiles for a number of reasons - availability of various color kits, image enhancement tools, profiling tools, the existence of different RIPs at the same site, etc.

This guide provides information about the following:

z The general concept of color matching used to achieve the best color matching results between all the HP-Indigo presses. z How to achieve and maintain color matching between different presses on the same site and between different sites. z Issues associated with using different Digital Front End (DFE) / RIP configurations with dedicated color profiles and tables for each printed job.

2 HP Indigo Press - related Color Matching Tools

Today the operator has 2 ways of controlling the job color: z Digital change through the job look-up tables (LUT). The LUT defines the relationship between the dot size as defined in the image file and its size on the printed output (Figure 2, Figure 3). This should be the first option used to control the color of a job. z In the job Color Match tab, using the sliders to modify the Dot Area (DA) and Optical Density (OD) (Figure 5, Figure 6). The DA is the percentage of printed area on the substrate, and the OD is proportional to the thickness of the deposited ink (Figure 4). This tool is less predictable, and should be used only if necessary color match cannot be achieved after modifying LUT tables. Job LUTs can be used for last minute changes to a job. Five default LUTs are supplied with the press: linear, chromalin, and three LUTs in between. z You can create customized LUTs and apply them to any job. z You can change the job LUT using the brightness and contrast sliders to correct the look of the printed image. z Changing a job's LUT does not require re-RIPping. In the following example, colors are modified using the job LUT.

Figure 1: Job LUT Example

3 Figure 2: Color Control using the job LUT- HP Indigo 7000 Digital Press Example

Figure 3: Color Control using the job LUT - HP Indigo press 5500 Example

Figure 4: Dot Area and Optical Density

Dot Area

Optical Density

4 Figure 5: Color Control using Dot Area and Optical Density - HP Indigo 7000 Digital Press Example

Figure 6: Color Control using Dot Area and Optical Density - HP Indigo press 5500 Example

5 Color Profiling A color profile is a set of data that characterizes a color input or output device, or a . Every device can have its own color space

Profiles describe the color attributes of a particular device or viewing requirement by defining a mapping between the device source or target color space and a profile connection space.

Color profiles/conversions are used to convert colors from different color spaces. For example from RGB files to CMYK or from one CMYK space to another CMYK space.

Conversions of RGB to CMYK are generally done through systems, using color profiles that describe the spaces being converted. The conversions cannot be exact, since these spaces have very different and since RGB and CMYK spaces are device- dependent.

HP Indigo provides a number of color profiles in the DFE that can be used for different applications in the press (e.g. Pantone matching, photo applications, etc.)

If the embedded HP color profiles are not suitable to customer needs, a new color profile can be defined and used according to customer preferences.

Color appearance can be modified using specific profiles to meet the customer application needs.

Evaluating Color Match

The eye is the most sensitive tool for comparing colors, and most customers aim to achieve visual color matching.

Some customers will have their own internal measurable specifications using their own Print Quality test jobs.

HP Indigo provides CATP, Optical Density, and Dot Area specifications.

As a first step to achieving color match, HP Indigo recommends to perform all the calibrations procedures on the presses. Afterwards, evaluate the color matching visually, using the real customer job. From our experience in most of the cases this will match the customer needs.

When attempting to color match from an HP Indigo print to another non-HP Indigo printing device, then application of the color profiles/Pantone tables should be considered. This will have implications for future color match between HP Indigo presses.

It is recommended to modify the color profiles on the non-HP Indigo devices first.

If the color profile is modified on one HP Indigo press, then the same change must be implemented on all HP Indigo presses in order to achieve color match.

6 Best Practice

Based on extensive tests conducted by HP Indigo, no fundamental has been seen between the various HP Indigo presses. Two HP Indigo presses will have the same color differences as two similar devices including printing during a long time or after a few days.

Color profiles should be set once if needed. Regular press calibrations is the best tool for maintaining the color consistency on the press. z Color profiles should not be modified or manipulated to match color between different HP Indigo presses, and not for stabilizing the color on a specific press. Modification of color profiles only causes additional color problems and prevent color matching of returning jobs. z Press Calibration - The color stability of the press can be maintained by calibrating the press properly. This is true for color consistency (along time and between presses). The recommended press calibration frequency depends on the color requirements of the client, and printed application. Generally better color consistency is obtained when the press is calibrated often.

7 Calibrating for best color match This section describes color calibration procedures for achieving the best color consistency achievable for HP Indigo presses. If an accuracy issue arises for any reason (e.g. Pantone matching not acceptable), additional matching must be done in the pre-press stage.

Note that calibrating for best color match consumes a larger amount of substrate and time compared to the automatic default press calibrations. The procedure is specifically designed for customers wishing to achieve high color performance and who have low sensitivity to increased waste.

Pre-calibration

Note For HP Indigo W7200 Digital Press, HP Indigo press w3200 and HP Indigo press w3250: The following procedures should be performed on both engines at the same time to avoid color differences between the two engines.

This procedure can only be effective on a press that is well maintained:

1. Make sure that all regular maintenance routines have been performed. 2. Check the ink density and conductivity. (This should be checked at least once a month.) 3. Make sure the X-Rite (500 series) external densitometer is: • Calibrated using it's own ceramic plaque • Operating status is "G" • Set to absolute mode

Substrate definition Do the following for all substrates:

1. Edit the substrate properties shown in the Substrates List. Make sure that the Color Control Data From field is set to Own or Own Parameters. 2. Make sure the optical density (OD) of each substrate is accurate. Insert a white opaque paper and measure the OD of each substrate with the same external X-Rite densitometer used to calibrate the ILD (In-line densitometer). 3. Make sure that the substrate type definition is correct (gloss, semi-matte, matte). 4. If the substrate gloss level is unknown, refer to “Determining substrate type” on page 17.

8 Figure 7: Edit Substrate Properties window - HP Indigo press 5500 Example

Figure 8: Edit Substrate Properties window - HP Indigo press 7000 Example

9 Achieving the best color matching between HP Indigo presses When more than one press is present, perform the following steps to achieve the best color matching between the various HP Indigo presses:

1. Perform a Full ILD Calibration on all presses at the same time (or as close as possible). Recommended frequency: • Not more than 2 months after the previous Full ILD Calibration for all presses at a site. • When color difference problems occur. • When the press software recommends a Full ILD Calibration. • When the ILD is replaced. 2. Use exactly the same calibration sheet for all the presses. If there are web presses present, use exactly the same external densitometer for ILD calibration. 3. Perform either the Machine LUT generation or the Full Color Calibration for all the presses (see below).

Note Do not use the Short Color Calibration or the Color Adjust Calibration.

4. Use the same Substrate Hierarchy for all presses. 5. Use the same Screenings for all presses. 6. Matching between different substrates can be very difficult. To achieve color matching between the presses, try using the same substrate on all the presses. 7. Use the same color strategy and the same color conversion (including Pantone tables) for all the presses.

Note HP Indigo R&D conducted color consistency tests over extensive periods of time, and found no fundamental color differences between the various HP Indigo presses. In general, color profiles should not be modified or manipulated to match colors on other HP Indigo presses. This will only cause additional color problems and prevent color matching of returning jobs. To match colors across HP Indigo presses, use exactly the same color strategy and RIP engine on each press.

To achieve color matching across multiple sites, see “Color matching procedure for multiple sites” on page 15.

10 Figure 9: Full ILD Calibration

HP Indigo press 5000 example

HP Indigo 7000 Digital Press example

11 Color Control Procedure

Note The following calibrations consume more substrate and time compared to the default automatic calibrations.

1. Machine LUT generation/Full Color Calibration. The Machine LUT generation/Full Color Calibration should be performed: • Every day for every substrate used. • Before every long run. • Whenever color deviations are noticed during the run. • Perform the Machine LUT generation/Full Color Calibration once every 6k impres- sions to 20k impressions for HP Indigo press series 3000, HP Indigo press series 5000, HP Indigo press series w3200 and HP Indigo press series ws4000. • Perform the Full Color Calibration once every 6k impressions to10k impressions for HP Indigo 7000 Digital Press, HP Indigo WS6000 Digital Press and HP Indigo W7200 Digital Press.

Note The color calibration frequencies listed above are general guidelines. Select a frequency that suits the required level of accuracy and type of application.

2. Blanket The blanket should have at least 3k impressions, without any severe blanket memory, before performing a Machine LUT generation / Full Color Calibration. If this is not possible, make sure that another Machine LUT generation / Full Color Calibration is performed when the blanket reaches 3k impressions. 3. Color Calibration Perform a Color Calibration. If the Color Calibration fails (on one or both print engines) do not continue to the next step, because this may cause color difference problems. Repeat the color calibration procedures until they converge successfully. 4. Quick Densitometer Calibration Perform a Quick Densitometer Calibration every week for all presses at a site. 5. ILD accuracy check (Color Adjust / Short Color Calibration) Perform a Color Adjust / Short Color Calibration once a month on the screens and commonly used substrates: • Using a correctly calibrated external X-rite densitometer, compare the optical density (OD) readings of the solid patches on the last page printed. (Make sure that there is a white opaque background beneath the solid patch.) • If a measurement for any of the 4 process colors varies from the ILD measurement (as presented in the press user interface) by more than +/-0.03, then perform a Full ILD Calibration procedure.

Note Perform this calibration for all HP Indigo presses at a site, at the same time, to avoid possible color differences between presses.

12 Calibration guidelines z The Full Color Calibration is more accurate than the Short Color Calibration. Therefore, the Full Color Calibration should be performed more frequently instead of performing the Short Color Calibration on HP Indigo 7000 Digital Press, HP Indigo WS6000 Digital Press, and HP Indigo W7200 Digital Press. z The higher frequency of calibrations on HP Indigo 7000 Digital Press, HP Indigo WS6000 Digital Press, and HP Indigo W7200 Digital Press maintain a higher level of performance than in HP Indigo press series 3000, HP Indigo press series 5000, HP Indigo press series ws4000, HP Indigo press w3200/w3250. z The Machine LUT generation / Full Color Calibration and the Color Adjust / Short Color Calibration should be seen as components of a broader toolset, and not as stand- alone tools.

Figure 10: Full Color Calibration Wizard - HP Indigo 7000 Digital Press Example

Figure 11: Full Color Calibration Wizard - HP Indigo press 5500 Example

13 Figure 12: Short Color Calibration - HP Indigo 7000 Digital Press Example

Figure 13: Short Color Calibration - HP Indigo press 5500 Example

14 Achieving the best color matching between sites Customers with presses at a number of sites can improve color consistency across sites by: z Standardizing DFE color settings for all sites z Ensuring same color calibration of presses at each site and across sites

Standardized color settings The following color-related settings should be consistent across sites: z Screening z Default LUTs z For the same job - Dot Area and Optical Density settings (see Figure 5 and Figure 6)

Standardized press calibration procedures Refer to “Best Practice” on page 7.

Color matching procedure for multiple sites

The following procedure brings all presses to a common calibrated state. When this procedure has been performed at each provider site, presses across multiple sites will be closely aligned. It is important to perform the whole procedure in one day.

1. Substrate definition: Ensure that all substrate type and optical densities (if needed) are accurate as measured by the same external X-Rite densitometer that is used to calibrate the ILD. 2. Master press ILD calibration: a. Select a press to function as the master press for all future master calibration work. b. Perform a Full ILD Calibration on this press using the calibration substrate. c. On the final calibration sheet, for each color patch, write down the average of the 4 OD measurements taken by the external densitometer. This calibration sheet will become your master calibration sheet to use on all of your presses. 3. Secondary press ILD calibration: For the remaining presses on site, perform the following procedure a. Using the master calibration sheet and the exact same substrate, perform a Full ILD Calibration. b. The ILD calibration wizard will request the color OD measure values from step 2c above and the measured paper OD values. c. The automatic color calibration should be enabled in all presses with no bypass on the color calibration. 4. Full color calibration: For all presses on site, including the master perform the following procedure: a. Perform a single full color calibration for the screen frequency used. b. From the color calibration printed sheets, take the last printed copy with the solid patches. c. Measure the CMYK solid patches on this calibration sheet with the external densitometer.

15 d. Compare this result with the ILD measured Solid ODs that appear on the color calibration result screen in the wizard. e. If the results are greater than +0.02 OD off, repeat the steps for Secondary Press ILD Calibration for this press. 5. Full ILD Calibration: • Use only the calibration substrate (glossy type is recommended) for the Full Densito- meter Calibration. • It is highly recommended to use the exact same calibration sheet for the Full Densito- meter Calibration on all presses.

16 Determining substrate type Perform the following procedure to determine the substrate type (glossy, semi-matte or matte) for different substrates, including plastic and transparent substrates.

Note Prior to performing the procedure, make sure the ILD is well calibrated.

1. Load a well defined substrate into the press. A high gloss substrate is highly recommended. However, if its not available, use another substrate whose type is well know (e.g. gloss, semi-matte, matte) and defined. 2. Make sure that the known substrate is defined as a calibration substrate in the Substrate Properties, and installed on the press. 3. Perform the Color Adjustment/Short Color Calibration procedure. Make sure it converges successfully for all colors. (Velectrode calibration is not needed. In the Select Method of Substrate OD Usage field, select Read Substrate OD).

Figure 14: Custom Color Adjustment Wizard - OD Step

4. Load the desired unknown substrate on the press. In the substrate list, make sure that it is attached to the known substrate that was used for the color calibration. 5. Print 10 copies of the CATP job. 6. Measure the solid patches (J area) in the 9th and 10th copy of the CATP printout. Insert a white and opaque background underneath the printout. 7. Check the measured values for each ink and compare to the values specified in the following table. Find the substrate type that most closely resembles the measured solid OD values.

17 Table 1: OD values by color for different gloss levels

Yellow Magenta Cyan Violet

Matte 0.9 1.1 1.1 1.2 1.3 1.1 1.1 (0

Semi-matte 1.0 1.3 1.3 1.6 1.65 1.3 1.3 (12

Gloss 1.1 1.45 1.45 1.75 1.9 1.45 1.45 (Gloss >25)

8. In the Substrate list, edit the desired substrate (see Figure 7and Figure 8). Select the Type/Gloss Level that matches the measured solid OD values (gloss, semi-matte, matte). This field may be disabled while the substrate is installed in the press. Therefore the substrate may have to be uninstalled in the press software before you change its type, and then be re-installed. 9. Change the desired substrate to be a calibration substrate (Color calibration parameters - Calibration Substrate; or Use Color Control Parameters From - Own). 10. Perform a Short Color Calibration on the tested substrate. Make sure that the wizard completes all of its steps, and that all colors pass the Color Adjust procedure.

Exceptions and troubleshooting z If the color calibration fails when adjusting the 100% OD values, the problem is probably associated with the substrate type definition. z If the color calibration fails due to the developer voltage being out of range (too low or too high) the issue is probably related to the wrong substrate type definition. For developer low limit failure, select a glossier substrate type. For developer upper limit failure, select a less glossy substrate type. z Unlike CMYK process colors and Orange and Violet special colors, IMS colors are mixed for specific substrate types. Therefore, the color adjust setup OD of 100% spec. values will not change with different substrate types.

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Copyright © 2009 Hewlett-Packard Company

This is an HP Indigo digital print. www.hp.com/go/indigo

P/N: CA394-03840