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- Note which version of standard you are using. Each color standard values vary based on the version and the manufacturer of the standard. The XRite Colorchecker 2019 (MacBeth standard, Figure 5) is the preferred card to use for calibration. The program is set up to use the White and Black squares on the XRite Colorchecker (MacBeth standard). On the Xrite color checker standard the RGB values of White and Black are listed here for various illuminants. White RGBs are 242, 242 and 236 and and black RGBs are 49, 49, 50 (those values are calculated using illuminant D65), as of there is discussion that we will use RGBs calculated under illuminant A as it better matches our LED lights, please note that using . Using illuminant A the RGBs for white is 240, 242, 235 and black is 50, 50, 50) . For the QP 101 v4 card, the RGB values are 235, 235, 235 (light grey), 111, 111, 111 (medium grey), and 80, 80, 80 (dark grey) (Figure 6). All SHIL calibration standards are found in drawer PP-2B.
- Obtain the 3D standard (Figure 5) and the gray silicone mat standard from PP-2B.
- Set camera f/stop to either F/16 or F/22 (Figure 7). The camera manufacturer suggested F/22 as the preferred f/stop for scanning with the our light set up however we have found F/16 works well for our section halves and is the most used f/stop for calibration and scanning sections. For hard rock cruises, where 360° whole round scanning is required, a larger f/stop number maybe required.
- If you haven’t set the camera’s height, now is the time to do so! See the section Camera Height Adjustment at the end of the calibration section. The camera height should not need to change between expeditions.
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10. Adjust the Green Exposure Interval value until the RED/GREEN value is as close to 1 as you can achieve. near 1 (Red is 240, Green is 242)
11. Adjust the Blue Exposure Interval value until the BLUE/GREEN value is near 1 (actual ratio <1, Blue is 235, Green is 242).
12. Don't worry about getting too close to value of 1, the TIFF/JPEG correction will correct those values.
13. Turn lights off by clicking Lights Off.
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7. Important Note: adjusting those gains likely changed the RGB values in the White square of the Xrite Color checker. Move the camera back over the white square. Draw an ROI box in the white square. If the values aren't near 242 go back to the Rates and Exposure tab and adjust the the values until you hit near 242 (RGB 240, 242, 235). Check back in the Black square and see its still about 15. Adjust the gains and/or exposure intervals until the Black reads near 15 and White reads near 242 (RGB 240, 242, 235). This is a balancing act and can be tedious. Remember do not let the temperature to go about 39°C white doing the balancing. If all fails use the values in the Figure 43, they should be close to an acceptable color balance.
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4. Click Lights Off. At this point wait for lights to cool, turn lights back on and check the White square RGB values (242, 242, 236) again are near 242 and adjust the exposure intervals if needed.
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4. In the Compare tab check that the corrected color square and Xrite color checker RGB values are very close (Figure 40). Make sure that the white does not exceed the Xrite values (RGB = 242, 242, 236). There There is also a visual display so you can see the difference in color for the color checker and the corrected. If you are unable to produce a reasonable correction curve, it is necessary to redo your white balance correction described in the Calibration section below.
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