by Tom Lee Published 01/04/2014
Taking in the View
During the qualifications assessment the images are viewed under two sets of conditions. The panel in its entirety is assessed in tungsten light under conditions which deliver an incident light reading of 1/4s f11 at 100 ISO. The prints are individually examined under the more searching conditions defined by ISO 3663 Viewing Conditions - for Graphic Technology and Photography. This standard actually has two viewing illumination levels, P1 and P2. The GTI PDVe Print Viewers normally employed comply with most of the requirements of ISO 3664 although the prints have to be viewed almost vertically. Nevertheless ISO 3664 is a searching examination under bright, high-quality light at either 500 lux for P2 or 2,000 lux for P1.
P1 is recommended when comparing an original and its reproduction, or when comparing a sample print with a production run. The higher illumination level enables better judgment for evaluation of higher density zones. However, if is also recommended to make a comparison with the P2 conditions, or the actual conditions that will be used to view the images, to get an overall view of tone reproduction.
P2 is recommended when one wants to make a judgment on individual prints. This viewing condition is not recommended for comparing prints against one another, with the exception of comparing a print with its image shown on a monitor. The lower illumination level of P2 makes this task easier. You should be aware that such a comparison, monitor vs print, should only be performed when the monitor and print viewing light have the SAME white point, usually D65 or D50.
Replicating the above conditions usually requires a proper booth but you can get close using daylight-corrected bulbs in a desk-light holder (angle poise) or by installing graphics tubes, overhead, in a normal diffuser. Solux Units are tungsten halide based with daylight filtration and provide near perfect CRI values. You can obtain the correct luminaires from www.lightbulbs-direct.co.uk. Their Helix Daylight Energy Saver 30W BC/B22d has a bayonet fitting, 6400K temperature and a CRI of 80. Their F18W/72 2ft Activa 172 Full Spectrum Daylight Tube has a colour temperature of 6500K and a CRI of 98% in a two-foot,
two-pin, one-inch tube. Their Philips Graphica Pro TLD-90 18W/950 2ft has a 5300K colour temperature with a CRI of 98%. All are modestly priced in comparison to say the specialist Just Normlicht luminaires which cost at least three times as much. Colour Confidence have a comprehensive selection of both booths and lights including the modestly priced Grafilite desktop 'angle poise' lights.
For any real colour geeks, Danny Pascale of BabelColor has as really comprehensive review of lighting solutions and performance at http://www.babelcolour.com/download/Light_under_control_2005-11-08.pdf. The BabelColor website is a mine of information for those who are inclined!
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