Spectral tools - Graph
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Use the Graph tools to measure the spectrums of color patches (Reflectance mode), displays (Emission mode), and light sources (Ambient and Flash modes). (Note: As with all CT&A Spectral Tools, an Eye-One Pro is required. Also, some Eye-One models do not support all measurement modes). The screenshot above was obtained by measuring Sample-1 (S1) in Ambient mode and Sample-2 (S2) in Flash mode. Depending on the samples measurement mode, various operations can be performed, either on a single measurement or by combining two measurements. If your requirement is to formally assess the quality of a display or viewing environment, such as a light booth, then you should also have a look at the ISO 3664+ tools shown in the next screenshots. Returning to the screenshot above, the sample on the left (S1), drawn in black in the top graph, is a measurement of a common tungsten-halogen desk lamp. With a 2790 K Correlated Color Temperature (CCT), this lamp has a spectrum very close to Illuminant A; it has a definite yellow tinge compared to D65, the nominal display white point from which this screenshot was taken (in other words, the "xy" coordinates of the lamp, 0,4534 and 0,4103 in the screenshot, fall in a yellower area of the chromaticity diagram when compared to the coordinates of the D65 Illuminant). Its Color Rendering Index (CRI) is 99 when computed using a 2800 K blackbody as a reference (this reference is shown between parentheses below the CRI). The sample on the right (S2), drawn in red, is a measurement of a small digital camera accessory flash. The flash Illuminance was measured at 620 lux-sec; its color temperature is 6055 K and its CRI, calculated using D61 as a reference, is 97. The bottom graph of the same screenshot shows "S2 vs Illum.", where the S2 spectrum is reproduced, this time drawn in black, and compared with the spectrum of an ideal D61 source of the same brightness, shown in green. We see an excellent match between the spectrums for wavelengths higher than 430 nm. We could have made a similar comparison between the S1 ambient measurement and the 2800 K blackbody used as a reference for the CRI by selecting the "S1 vs Illum." button. The image below is an example of what can be obtained by clicking on the "Save image" button located in the bottom of the Graph tools dialog. Here we made two measurements in Reflectance mode and selected the "Subtract (S1 - S2)" operation. Sample-1, a purplish color, is a mix of red and blue while Sample-2 has a reddish-orange tint. By subtracting the reddish-orange form the first sample, what is left is essentially the blue portion of the first sample, with the difference spectrum and the resulting color patch shown in the bottom part of the image.
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