Spectral tools - ISO 3664 (Illumination analysis)
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ISO 3664 (Viewing conditions - Graphic Technology and Photography) is mostly a collection of standards regrouped to define the various viewing conditions required to judge the quality of color images. The P1 condition shown above, as defined in ISO 3664, is dedicated to the CRITICAL evaluation of prints under ambient light, or light booth illumination, at an illuminance level around 2000 lux. A similar interface is presented for the P2 and T1 conditions, respectively defined for PRACTICAL appraisal of printed color (at a lower illuminance level of 500 lux) and for the direct viewing of transparencies with backlit illuminators. Any viewing condition can be measured at up to nine positions, as selected in the "Brightness uniformity" section. In the screenshot above, the upper-left position is selected and the corresponding "Brightness", "Chromaticity", "Color Rendering Index (CRI)", and "MI" data is shown for this position. The "MI", or Metamerism Index", measured here is defined in ISO 23603 / CIE S 012 and presented as a Quality Grade for daylight simulators, from "A" to "E", with "A" being the best score. This is not the same MI as the one computed in the "MI tools". Combining the CRI data with the quality grade has been recognized as a very effective way of characterizing illumination. These tools are called ISO 3664 with a "+" to indicate that alternate reference illuminants can be selected by the user for each test. In the screenshot above, we have measured the illumination on a work table. Prior to our measurements, we had identified measurement locations on a 3x3 grid over a 1m by 1m area, corresponding to the nine positions. Because the ambient light was near 5000 K, we selected "Goal" as our target chromaticity, which is D50 in ISO 3664. We selected "D50" for the reference CRI Illuminant; the opened menu shows the other possible selections, including "Auto", which generally gives the highest CRI results by selecting the closest reference CCT (but the CCT may not be close to what you are looking for!). The MI reference was set at D50. We see that the brightness in the upper-left position, the position selected in the "Brightness uniformity" control group, is 1962 lux, meeting the P1 goal, and we thus see a "PASS" result. The CRI, MI, and brightness uniformity results for this position also pass the selected requirements. We see that the chromaticity test fails. We can look at the results for each position by selecting it in the brightness uniformity group and we can save all test data in a file by clicking on the "Save to file..." button. And we can also have a global snapshot of the test results by printing a one page report, shown below, which is useful for compliance reporting. We see that while the uniformity is good, the center position illumination is high. The CRI and MI results pass the requirements at all positions, but the chromaticity fails at all positions, with the CCT on the low side. A similar report is available for all viewing conditions. The ISO3664+ tools used for characterizing color monitors are shown next.
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