Implementing ISO12646 standards for soft proofing in a standardized printing workflow

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1 Implementing ISO12646 standards for soft proofing in a standardized printing workflow Aditya Sole Implementing ISO12646 standards for soft proofing in a standardized Gjøvik University College, The Norwegian Color Research Laboratory, Norway printing workflow Aditya Sole Gjøvik University College, The Norwegian Color Research Laboratory ABSTRACT: This paper defines one of the many ways to setup a soft proofing workstation comprising of a monitor display and viewing booth in a printing workflow as per the Function 4 requirements of PSO certification. Soft proofing requirements defined by ISO are implemented in this paper. Nec SpectraView LCD2180WG LED display along with Just colorcommunicator 2 viewing booth and X-rite EyeOne Pro spectrophotometer are used in this setup. Display monitor colour gamut is checked for its ability to simulate the ISO standard printer profile (ISOCoatedV2300%.icc) as per the ISO requirements. Methods and procedures to perform ambient light measurements and viewing booth measurements using EyeOne Pro spectrophotometer are explained. Adobe Photoshop CS4 software is used to simulate the printer profile on to the monitor display, while, Nec SpectraView Profiler software is used to calibrate and profile the display and also to perform ambient light and viewing booth measurements and adjustments. INTRODUCTION: Soft proofing can be defined as the ability to match colour images displayed on colour monitors to the images produced when the same digital file is rendered by proofing and printing systems [1]. ISO define parameters for monitor and viewing booth condition setup for soft proofing environment. The practical methods to implement these standards as per the job requirements are not been defined. This paper therefore, describes one of the ways to setup an appropriate soft proofing station (comprising of a monitor and a viewing booth with the appropriate ambient lighting conditions) according to ISO standards for soft copy and hard copy proof comparison in the graphic arts industry and evaluate the same. STANDARDS FOR SOFT PROOFING (SPECIFICATIONS): This paper primarily focuses on the scenario where soft copy is directly compared with the hard copy. The technical requirements are defined by ISO for this scenario as ambient illumination, surroundings and environment, Chromaticity, luminance of the white and black points, Colorimetric accuracy & grey balance of the display, Uniformity of display luminance. Table 1 below summarizes the specification and tolerances defined by ISO standards for soft proofing. Parameters Target Colour Intensity Chromaticity Uniformity Black point Temp Ambient light 5000 K ¼ monitor Uniformly -NAwhite point Diffuse Surround Neutral and matt with luminous reflectance between 10% and 60% Display 5000 K >80 cd/m 2 U = v = Viewing booth 5000 K 500lux ± 125lux u 10 = v 10 = % within the centre measurement for 1m 2 area, luminance = >75% luminance at the centre Table 1 Specification and tolerances according to ISO standards for soft proofing Luminance < 1% of max luminance -NA

2 PROCEDURE FOLLOWED FOR IMPLEMENTING THE CONDITIONS/ SPECIFICATIONS MENTIONED ABOVE: In this section methods and procedures are proposed for implementing the specifications mentioned previously. To setup the soft proofing station and the ambient light condition following apparatus was used: Hardware: NEC SpectraView LCD 2180WG LED display, Apple MAC PRO 10.4, Just Normlicht Colour Communicator 2 viewing booth, X-Rite EyeOne Pro spectrophotometer including ambient light measurement adaptor, OSRAM L58W/950, LUMLUX de LUXE, Daylight tubes for ambient light Software: SpectraView Profiler Version 4.1 (NEC SpectraView monitor calibration and profiling software), UDACT (UGRA Display Analysis Certification Tool) monitor certifying software by UGRA, Adobe Photoshop CS4 Nec SpectraView LCD 2180EG LED display was used as the display monitor to display the soft copy images. Nec LCD 2180WG LED is a high end display which features individual high power red, green and blue LEDs (Light Emitting diodes) as a backlight light source for the LCD, instead of the typical CCFL (Cold Cathode Fluorescent Lamp) [2]. LED backlight results in a wide output colour gamut of the display. Hardware calibration can be performed on this display using its own calibration and profiling software. Hardware calibration eliminates the need to correct the RGB output for smooth, accurate display of greyscale images. Nec SpectraView Profiler software calibrates and profiles the Nec LCD 2180WG LED display monitor. The software allows custom target calibrations that can be preset or can be defined by the user. The user can define the white point, light intensity, gamma curves, black point, etc. At the end it also profiles the display and generates a *.icc colour profile. Target and measured results are analysed and displayed, showing information like measured colour, colour difference, gamut etc [2]. Just colorcommunicator 2 viewing booth was used for the soft proofing station along with the NEC SpectraView monitor display. The light intensity of the viewing booth can be adjusted via software to match the light intensity of the display for soft proofing [6]. To perform the measurements of light intensity, white point, colour rendering on the monitor display and on the hard proofing a number of different measuring instruments can be used. To avoid inter-instrument uncertainty and reproducibility issue only one instrument has been used for the measurements [3]. For this setup, a X-Rite EyeOne Pro spectrophotometer was used to perform the measurements on monitor display and hard copy and also to perform the ambient light measurements using the ambient light adaptor. MONITOR CALIBRATION AND VIEWING BOOTH ADJUSTMENT: To calibrate the monitor and adjust the viewing booth following procedure was followed: NEC SpectraView Profiler Version 4.1 software was used to calibrate, profile and adjust the viewing booth according to ISO standards for soft proofing. P2 viewing conditions defined in ISO 3664 were setup in the viewing booth according to ISO specifications (ISO 12646;Sec 4.8.2). The target for ISO standards define the parameters as follows: Display Type LCD Calibration method Hardware calibration (monitor LUTs) Calibration settings ISO3664 and ISO Profile settings LUT based (accurate) CIE Daylight standard D50 Tonal response Curve L* (recommended) Specify White and black luminance White 160 cd/m 2 Black Minimum neutral Profile type 16 bit LUT based 2 222

3 Chromatic adaptation CAT02 Table 2 Preset target settings in NEC SpectraView Profiler software This preset target was selected for calibration and profiling the monitor display. Figure 1 shows the display monitor with the measuring instrument on it for calibration and profiling. After calibrating and creating the monitor profile, the profile was validated. After successfully validating the profile, the viewing booth settings were checked. Check viewing booth option was selected in the review column Viewing booth and monitor comparison and measurements were performed. To record the measurements, the measuring instrument was held parallel to the viewing booth facing towards the plane of viewing as shown in figure 1. Instructions on the screen were followed. Viewing booth conditions were checked against the P2 viewing condition mentioned in ISO The necessary adjustments in the viewing booth (for light intensity, etc) to match the ISO 3664 P2 viewing condition requirements were made. The viewing booth measurements were performed using X-rite EyeOne Pro with the ambient light adaptor. Figure 1 Schematic diagram and image of the position of the measuring instrument for viewing booth measurement AMBIENT LIGHT CONDITION SETUP AND ADJUSTMENT: The room used for the soft proof setup has a neutral and matt colour according to ISO 3664 (sec.4.3.4). To setup the ambient lighting conditions according to ISO standards for soft proofing, daylight tubes named OSRAM L58W/950, LUMLUX de LUXE, Daylight were setup in the room. These tubes simulate Illuminant D50 and the light intensity can be varied as per the requirements. Therefore, in order to vary the intensity of these tubes a varying knob facility was introduced in the room with which the ambient light intensity in the room could be controlled. Figure 2 shows the varying knob facility setup in the room and X-rite EyeOne Pro with ambient light adaptor. Figure 2 Varying knob facility and X-rite EyeOne Pro with ambient light adaptor X-rite EyeOne Pro spectrophotometer with ambient light measurement adaptor was used for measuring the ambient light in the room. SpectraView Profiler software was used to perform the ambient light measurements. To perform the measurements, X-rite EyeOne Pro was held straight parallel to the display facing towards the room (with the monitor switched off). Figure 3 shows the schematic diagram and the image of the position of the spectrophotometer to perform the ambient light measurements. The ambient light was measured for light intensity and colour temperature. As an alternative a number of software s like BabelColor CT&A, UDACT, etc can be used to perform ambient light measurements. RESULT: MONITOR DISPLAY: To analyse and evaluate the display for soft proofing environment the UDACT certifying software was used. UDACT analyses the display for the specifications according to ISO standards for soft proofing. UDACT records the measurements and generates a report at the end that shows all the details of evaluation

4 Figure 3 Position of the measuring instrument for ambient light measurement WHITE POINT AND BLACK POINT: According to ISO 12646, white point of the display should be as close as possible to the calibration target. Table 3 below shows the target and the measured values for white and black point. Target Measured Difference White point 5000 K 4991 K 0.5 ΔE ab Luminance 160 cd/m cd/m 2 Black point <1.6 cd/m cd/m 2 Table 3 White and black point of the NEC display GRAY BALANCE: The maximum allowed deviation shall not exceed ΔE c =3 and preferably not ΔE c =2 (ISO 12646, sec4.10). The maximum deviation obtained was ΔE c = 2.35 COLOUR GAMUT: The colour gamut of the display should be such that it totally encloses the colour gamut produced by the inks specified in the appropriate part of ISO for which the display is required to provide a proof (ISO 12646; Sec A.2). UDACT checks for the colour gamut by measuring the Ugra/Fogra step wedge 2.0 on the display simulating the ISO coated V2.icc profile. Figures 4 below show the u v diagram and L* Vs C* graph of the gamut of the monitor display and ISO coated profile. VIEWING BOOTH AND AMBIENT LIGHTING CONDITIONS: To analyse and evaluate the viewing booth and ambient lighting conditions, measurements were performed using the X-rite EyeOne Pro with the ambient light adaptor. Tables 4 show the target and measured viewing booth and ambient light conditions. SOFT PROOFING IMAGE DATA: Implementation of the ISO standard does not guarantee that a displayed (soft copy) image will match the colour of the same image produced on the hard copy (ISO 12646). To obtain a colour match, colour transformation is required to convert the colour data format from the printer colour space to the display colour space. This transformation is mainly done by means of a colour management system by using the ICC profiles. ICC profiles define the relationship between the device specific colour space and the profile connection space (PCS) (ISO 12646:Annex A.1). Adobe Photoshop CS4 software was used. Visual Print reference (VPR) images were used to simulate the ISO coated v2 300% (ECI).icc profile. These images were compared to evaluate the visual match between the VPR hard copy in the viewing booth and the soft copy on the display. To apply necessary simulation profiles a VPR image was opened in Photoshop. After opening the image, in Photoshop Menu, select, View Proof setup Custom. Doing so a window called Customize Proof Condition should open. Appropriate simulating profile was selected from the drop down. Simulating profile was the CMYK output profile that needed to be soft proofed (ISOCoated V2 300%(ECI).icc in this case). Image background was selected as neutral gray (similar to the viewing booth background). Simulate paper white option was tick marked to simulate the paper white and the images were then compared with the hard copy in the viewing booth. For the soft proofing task Adobe acrobat professional software can also be used to display the soft copy image on the monitor display. CONCLUSION: In this paper methods and procedures to setup a soft proofing station are discussed. ISO

5 Figure 4 Colour gamut of the monitor profile and ISO coated profile in the u'-v' colour space and L*-C* plane Illuminant Ambient Illuminant Illuminance Chromaticity Illuminance light Colour Colour Tolerance Lux condition Temperature Temperature (u v ) Viewing Booth Target 5000 K ± 125 Target 5000 K ¼ monitor white point luminance Measured 4995 K Measured 4853 K 103 lux Table 4 Viewing booth and ambient light condition target and the measured values standards for soft proofing were successfully implemented. The NEC LCD2180WG-LED monitor display used in this paper has a very wide colour gamut and was visually uniform. Gamut plots showed that the monitor display was able to simulate printer profile colours. Measurement procedures to measure ambient light using an EyeOne Pro with ambient light adaptor are discussed in this paper. The schematic diagrams and images of viewing booth and ambient light measurements show the position of the measuring instrument used to perform the measurements. NEC SpectraView Profiler software was used to perform the ambient light measurements. A number of different software s can be used to perform ambient light, viewing booth and display measurements. It was observed that, in spite of being within the ISO standards tolerance level the two images (soft copy image on the display and the corresponding hard copy image in the viewing booth) might not show an exact visual match. Therefore, the ambient light intensity and the viewing booth light intensity can be adjusted (within the tolerances defined by ISO 12646) as per different job requirements to get the closest possible visual match between the soft copy on the display and the corresponding hard copy in the viewing booth. REFERENCES: 1. ISO 12646:2008 Graphic technology Displays for colour proofing Characteristics and viewing conditions 2. NEC LCD2180WG-LED, (2005), NEC LCD2180WG-LED technical background and feature overview, NEC Display Solution 3. Nussbaum, P., Sole, A. and Hardeberg, J (2009) Consequences of using a number of different colour measurement instruments in a colour managed printing workflow, The Norwegian Color Research Laboratory, Taga ISO 3664:2009 Viewing conditions Graphic technology and photography 5. UGRA (2008), UDACT Ugra display analysis and certification tool, Help manual 6. JUST NORMLICHT (2008), Color communicator, Help manual 7. NEC (2008), SpectraView Profiler Version 4.1, User s manual 5 225