Color viewing booths are critical for evaluating digital output. What do you see?

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1 Color perception is highly subjective, individual, and affected by the substrate, printing process, and the viewing environment. Though these problems seem insurmountable, there are steps one can take to reduce surprises in final output. The governing bodies of the American National Standards Institute (ANSI, for the U.S. and the International Standards Organization (ISO, approve the standards we follow to ensure universal color communication. A recently updated standard (ISO 3664:2000), finalized last year, focuses on evaluating digital output. Another standard (ISO 12646), still in the works, addresses computer display soft proofing comparison to digital output. Color viewing booths are critical for evaluating digital output s more and more photographers migrate to a digital workflow, many quickly become frustrated by the discrepancy from screen to print or facsimile to an original. Some have braved the tumultuous waters of implementing color management in hopes of reducing the gap from screen to print. Few realize the importance of the viewing environment when evaluating color output. The environment in which you view your prints has a profound effect on your color perception. Strongly colored objects or walls can influence your perception. The type of light source used is a significant factor. Cool white fluorescent bulbs look quite different from a tungsten soft white bulb. The light illumination level, or lux, can vary considerably too. What do you see? When you research viewing booths, ask first what you hope to attain from the device. Do you want your computer screen to simulate print output? Maybe you are concerned about how your inkjet prints compare to a proof or match original artwork (painting, photograph, object) to a digital reproduction? Do you need to evaluate how different light sources effect color and tonality? Determine your goals beforehand. ISO 3664:2000 is an updated recommendation for critical evaluation of digital output. The recommendation defines the variables of room (ambient) brightness, viewing booth white point and brightness level, surrounding surface colors, and tolerances within each variable. The ISO 3664:2000 intentionally does not go into detail on how to soft proof final output on computer display, instead focusing on the environment for critical comparison of digital reproduction to an original or proof. ISO 3664:2000 was jointly PEI NOVEMBER

2 updated by the ISO Photography and Graphic Technology boards. The goal of the updated standard is to minimize the differences between viewing environments. Without exception, the best viewing environment is that in which the image will be finally seen your target environment. Proper targeting ensures the best quality reproduction. Unfortunately, you don t always know where the prints will be viewed. The revised ISO standard defines color viewing conditions without regard to final viewing environment, eliminating the final variable in a color managed workflow, making consistent color standards with your print provider and local output devices achievable. A high amount of ambient light impedes the match from Apple's Cinema Display to the light box. Reducing the ambient light intensity to around 32 lux eliminated the flare and ambient light contamination, resulting in an almost ideal match. What do you need? An ideal viewing environment has equal energy across the visible and ultraviolet color spectrum. The ultraviolet spectrum is important where fluorescent brighteners are present in the substrate and printing primaries. Therefore, ISO 3664:2000 uses the CIE (International Commission on Illumination, reference illuminant D 50. A bigger consideration is compatibility with current color measuring hardware and software used to create ICC compliant profiles. The ISO 3664 revision lists two levels of illumination in evaluating digital output. The two illumination levels are for judging and exhibiting digital output. The first luminance level, P1, is significantly higher than normal viewing environments so that the viewer can distinguish small differences in color and tonality when compared to a reference. The lower illumination level, P2, recommendation more closely resembles illumination levels common in offices, galleries, and stores. The recommendation for P1 (critical comparison) is 2,000 lux ± 500 lux and should be within ± 250. In contrast, P2 illumination is 500 lux ± 125 and the tolerance level is smaller. For viewing areas one meter square the illumination may not fall off more than 75 percent from the luminance level in the center. For larger areas, the requirement is reduced to 60 percent. Lux is a measurement of lumens per square meter. To measure light in Lux units, refer to a conversion table from EV (exposure value) to lux, often listed on the back of light meters. For instance, 2,800 lux is EV 9 and EV 8 is 1400 lux. If I can get the viewing booth s illumination close to an EV 8.5, I will be within tolerance of the 2000 lux target level. This is not a precise technique, but you only need to get the luminance level in the ball park. Manufacturers lax on conformance Though some product manufacturers reviewed claim conformance to ISO 3664:2000 specification, it is a broad statement with little definition. Some, if not all, of the evaluation units conformed to part of the recommendation, but I feel all failed to provide a viewing environment that met the recommendation completely. It is difficult for a fluorescent light bulb to match the spectral power distribution of reference illuminant D 50 without distortions. Distinct spikes are evident in portions of the visible spectrum and drop off in the UV spectra. A filtered tungsten halogen bulb design achieves a better spectral match to the D 50 reference illuminant. Both GretagMacbeth and Tailored Lighting offer products that use filtered tungsten halogen technology. This graph illustrates the differences between the reference illuminant and simulator bulbs. The colored rainbow is a plot of CIE D50 illuminant. The reference illuminant has fairly uniform energy in the RGB and CMY portions of the spectrum. The blue line shows the close proximity of a filtered tungsten halogen bulb to the reference illuminant. The spiky yellow curve depicts a typical D50 fluorescent simulator bulb. You will see green/yellow and purples a lot more in a fluorescent tube design with little excitation in the red/magenta spectrum. Image courtesy Tailored Lighting. Some of the reviewed viewing booths offer a UV bulb that can be used in conjunction with other light sources to determine the presence of fluorescent brighteners in papers and inks. The perceived color improved when I engaged the UV bulb with a D 50 fluorescent simulator bulb. Papers that did not have optical brighteners did not benefit from 38 PEI NOVEMBER 2001

3 the UV bulb nor did the UV bulb cause problems. The ISO 3664:2000 recommendation assumes a company will buy a spectroradiometer to measure conformance with the reference illuminant and lumination level. This type of color measurement instrument, more than triple the price of a desktop color booth, is out of reach for most photographers and studios. ISO 3664:2000 recommends using CIE Publication No.51, 1981: A method for assessing the quality of daylight simulators for colorimetry to evaluate the simulator bulbs match with the reference illuminant. GretagMacbeth also retails LightSoft, Windows software that follows the CIE Pub. 51 standards. The program interfaces directly with their spectroradiometer. The hours used and frequency of turning bulbs on or off weighs heavily in the quality and stability of a viewing booth. When a bulb is turned on, the life span is diminished. Powering the booth off and on diminishes the life span more than continuous usage. Not all manufacturers factor in this variable. Some booths do not come with a usage meter. At the very least the manufacturer should specify the average hours of use the bulbs are expected to remain within specification. GTI Soft View Building upon their highly successful SoftView, the new GTI models are easy to assemble and provide simplistic operation. The SoftView has the smallest footprint and supports both reflective and transmissive originals. A couple of masks are included to allow hard copy and transmissive viewing at the same time. The masks go over the transmissive viewing area so there isn t any illumination from behind the print. The GTI unit reports hours of use on a distracting digital display that cycles between lamp hours and illumination level. I would have liked an option to dim it or turn it off. Adjusting light intensity incrementally for both reflective and transmissive is easy. Up and down arrows provide a precise method of dialing in an exact intensity level, which is recalled when you turn the viewer on. An audible indicator confirms changes in intensity. Designed to be placed close to a computer display, the SoftView s removable side walls prevent light from hitting the screen and ambient light from contaminating the viewing area. GTI recesses the reflective lights above the viewing area. Mirrors concentrate the light at the proper angle to minimize glare. Copyholders for both reflective and transmissive originals hold items flat against the vertical plane to maintain proper viewing angle. With the GTI, it was very easy to get the luminance level close to both intensity levels of ISO 3664:2000. The booth does not come with a UV bulb to evaluate fluorescent brighteners impact on color, but one can be added on special request. The MSRP for the GTI SOFV-2e is $1,365. ( Just-Normlicht Color-Match 5000 Duo The Color-Match 5000 Duo is designed for the professional needing to compare transmissive originals to prints. It has a large transmissive viewer equipped with a dimmer control to adjust the intensity to match either your monitor or balance the illumination intensity to the reflective light source. This booth uses an indirect lighting method to ensure glarefree viewing. A single fluorescent tube matched to 5,000K illuminates the reflective prints. A separate dimmer slider for reflective prints is provided to adjust the intensity to match either your transmissive original or computer display brightness. Small magnets and a copyholder help keep the print flat at the correct viewing angle. A cover slide at the top unit shields against light contamination on the transmissive viewing area. The Color-Match 5000 series has no sidewalls to block ambient light. If the viewer is placed too close to a monitor that does not have a hood, light spill and glare on the computer screen could pose a problem. The Color-Match 5000 Duo is available with a small transparency viewer in the base of the unit suitable for 35mm and 120mm films. The transparency viewing area of this model is 3.33x15 inches. The model sent for review has a transparency viewer to handle full 8x10 films (viewable area 12x10 inches) on the vertical print plane. You can view an 8x10 print along side an 8x10 transparency. The Color-Match 5000 Combi model allows either reflective or transmissive viewing but not at the same time. The Duo model allows simultaneous transmissive and reflective viewing. The maximum intensity setting on the booth had a distinctly different color temperature when compared to a lower setting. Calibrating to 2,000 lux was achieved by dimming the intensity slightly. Surprisingly the color temperature mellowed out at 2,000 lux and looked more consistent with the lowest setting, registering close to 500 lux. The calibration of each illumination level of ISO 3664:2000 P1 and P2 were easily met. No UV bulb is provided to check fluorescent brighteners impact. The Color Match 5000 also PEI NOVEMBER

4 does not include hours of use meter. Instead, Just-Normlicht recommends replacing the bulbs annually. The MSRP for the Pantone 3- Light booth is $855. The 5-Light booth is priced at $1,395. ( Pantone Color Viewing Light [PVL-511] (5 bulb version The Pantone Color Viewing Light is designed for the graphic professional needing to simulate different lighting conditions. The Pantone Viewing light is available in three or five light configurations. The three-light viewer includes two D 50 fluorescent tubes, two cool white fluorescent tubes, and two incandescent bulbs. The five-light viewer adds D 65 and UV light bulbs. The UV bulbs are helpful to determine fluorescent brighteners. The viewer is equipped with an electronic display and touch pad to select an illuminant to simulate. The display indicates the light source and the remaining hours of operation before needing replacement. The booth includes a relamp countdown for each illuminant independently. The digital control panel monitors the use of each bulb much like an odometer. After a preset amount of time and taking on-and-off switching into account, the display will notify the operator that the bulbs need to be replaced. An additional indicator on the unit provides quick verification if the bulb needs replacement. The operator can only view one illuminant at a time. The exception is the UV exciter bulb in the five-bulb unit. The UV bulb can be engaged while viewing with a reference illuminant. Pantone s light booth provides an automatic switching mode to Two prints viewed under Tungsten, illuminant A, lighting look very similar. Engaging the Ultraviolet bulb (top) shows that the left print has optical fluorescent brighteners added while the Fine Art paper does not glow like the adjacent print. compare the effects of different illuminants. Only one automatic cycling program is allowed, so different lighting combinations need to be programmed each time. The Pantone Viewer is ideal for evaluating three dimensional objects. Prints are laid horizontally on the floor of the booth. There is no provision for copy holding at an angle. Each illuminant is arranged with one bulb towards the back of unit with the other bulb in the front. The UV bulb (only available in the five light unit) is dead center with the incandescent bulbs on each side of the UV bulb. There is no electronic dimmer. The Pantone viewer is ideal for comparing the metameric effects of different illuminants but is not designed for comparison to computer screen soft-proofs since the intensity of the unit can not be adjusted. Sidewalls are neutral gray and extend enough to exclude ambient light and shield the viewing light from an adjacent computer screen. The Pantone booth was designed to meet ASTM (American Society Testing Materials) D1729 standard, Standard practice of visual evaluation of opaque materials and not ISO 3664:2000. The D1729 standard is applicable only in the U.S. and not internationally. Viewing booths that meet the ISO 3664:2000 standard also comply with the US D1729 standard. The MSRP for the ColorMatch 5000 Duo is $1,390. ( What about your monitor? ISO 3664:2000 intentionally did not go in-depth into the complexity of proper calibration and optimization for current CRT and LCD technologies when comparing to a hard copy. ISO Color proofing using a color display will address procedures to optimize color display performance prior to characterization (ICC profiling). A working draft outlines a procedure to validate if a monitor s color volume includes the printer color gamut. This recommendation is far from becoming a standard. Visit for the status of the proposal. In real life, CRT luminance levels are normally much lower than the brightness levels in a viewing booth. The brighter the monitor the less compensation is needed at the viewing booth to equalize perceived brightness levels. Apple s Cinema display has a much higher luminance level than most CRT monitors. I found I did not have to reduce the viewing booths intensity as much to match the Cinema display. I used GretagMacbeth s Eye one ( monitor calibrator to optimize and generate an ICC compliant profile for the display. Because I was able to get a brighter luminance level on the Cinema 40 PEI NOVEMBER 2001

5 Apple's Cinema Display is ideal for monitor-to-print matching. The higher brightness level minimizes the compensation needed to get the booth's brightness to equalize with the LCDs. display, my perceived white at D 65 matched a littler better to the viewing booth s D 50 bulbs. Conclusion: After calibrating each viewing booth to approximate 2,000 lux, I noticed distinct differences in the perceived white points of each booth even though each booth claims a D 50 white point and relative spectral match. The Just-Normlicht Color Match 5000 appeared to have the most balanced light source of the group. Both the Pantone and GTI booths appeared to have slight, but discernable, color casts. The GTI and Just-Normlicht booths were designed to hold a sheet at a 45 degree angle. The Pantone and GretagMacbeth booths do not provide a copy holder. Prints are laid flat across the bottom of the booth, which makes glare more of a problem. The booths that had a copy holder were much easier to view. None of the booth designs made it easy to calibrate and meet the ISO recommendation. There could be enough variance between booths in a shop to pose a problem for consistent viewing conditions. Currently, calibration is done visually and no statistical data is provided to validate a manufacturer s claimed conformance to the D 50 reference illuminant. I would like manufacturers to provide the classification A D used in CIE Pub. 51 to determine the accuracy of the simulator bulb. Unless a shop invests or has access to a spectroradiometer, it is impossible to determine if the booth meets at the onset, or after extended use, the target criteria of ISO 3664:2000. Dan Reid is senior trainer for Renaissance Photographic Imaging, a small company in Santa Fe, New Mexico, focused on helping businesses and individuals migrate to a color managed workflow. Dan can be reached at dreid@rpimaging.com. The art of lighting by PHOTOFLEX Photoflex SilverDome uses advanced technology to deliver unsurpassed heat-resistance, durability, and brilliant, natural light. Vincent Versace I use Photoflex for just about every lighting situation because the lighting I create with it is natural, clean and simple. Vincent Versace Versace Natural Light Studio For a dealer near you call or visit us online at PEI NOVEMBER