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The laboratory technician calibrates the system when needed by adjusting camera settings and analyzing an imaged XRite Color Checker Standard (MacBeth card) or a QP 101 V4 Color Standard. The current light system obtains nearly uniform illumination intensity from the core’s surface (half or whole round) to the bottom of the liner by a combination of high intensity, overlapping large diameter light source, close coupling to the imaged surface and the “line” image plane. The bottom edge of the brass led mount should be set between 2 and 4cm from the image surface. For uneven hard rock cores the height can be set higher but illumination intensity will drop, exposure times lengthen, f-stop opened and scanning speed reduced. Note, any height change to the lights requires re-calibration. Heat is removed from the LEDs and transferred to the surrounding air via the copper heat pipes and is cooled with mini fans. While the copper rods can get hot they are not a burn hazard. However they are very delicate and bend at the slightest touch, so use care when working with the camera lens. For more detailed information on the theory behind the calibration please refer to the Understanding the SHIL Calibration for further reading. Maintain temperature of the lights at 30-35 40 °C during calibration. LED's of temperature is located above the camera.
Note: The following instructions are divided into 2 sections: Calibration Check and Calibration.
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3. In the Tiff Correction tab adjust the LUT polynomial order values for the Red, Green, and Blue channels (Figure 15-1). Adjust these values to create the lowest residual error with the smoothest curve in the Uncorrected Image tab. Polynomial values should be about 3. Make sure that the curve does not wave about too much. If it does, the values need to be lowered. Also check that the corrected ROI and Xrite color checker values are very close. Make sure that the white does not exceed the Xrite values (RGB = 242, 242, 236). If you are unable to produce a reasonable correction curve, it is necessary to redo your white balance correction in the Calibration section below.
Figure 15. Tiff Correction
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2. Adjust the Brightness, Contrast, and Gamma levels (Figure 17-1) to achieve a straight line in the Applied Corrections tab and the RGB Corrected values in the Compare tab should have values near 242 for the white square and near 50 for the black. We want a linear relationship between the measured and given values. Each BCG setting adjusts the line in different ways and there are many different ways to adjust the values to achieve a linear relationship. You want to achieve a good image with good brightness, where the image has good saturation and not too washed out. The Applied Corrections Graph should be a straight line and the ROI Corrected Box should have values near the RGB values of 242, 242, 236. These may change depending on the instance of extreme colors, extremely white or extremely dark cores, in which the settings may have be tweaked more to get a user friendly consumer image.
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1. Confirm the camera f/stop is set to F/16 or F/22 (Figure 1518). F/22 is preferred by the camera manufacturer for scanning with the current light set up however the reasoning behind that is unclear. The imaging specialists onboard have been using F/16 and are confident F/16 works for our set up. For hard rock cruises, where 360° whole round scanning is required, a larger F-stop number maybe required (ie. F/22).
Figure 1518. Setting the F Stop on the Camera.
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2. In the IMS control panel select Motion and then Drive Disable from the dropdown menu (Figure 1619). You will have to move the camera by hand for the calibration, disabling the motor allows manual movement of the camera on the track.
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3. In the IMS control panel click Instruments > JAI Camera Settings (Figure 1720). The lights turn on automatically when the JAI Camera Setup window opens.
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