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- Color Standard values vary based on the standard and the manufacturer of the standard. Verify the values of the MacBeth Color Standard (multi color squares on the 3D standard, Fig ##) before starting (How do we do this?). Check the grayscale card to determine what the percentage of gray. The target calibration values will vary based on the percentage of gray because the target values depend on the percent grayscale card. Max RGB value is 255. If using a 50% grayscale card, target red and green value is 127, a 25% grayscale card target value is 64, etc. For our QP 101 v4 card, the RGB values are 235, 111, and 80 (Fig. ##). All SHIL calibration standards are found in drawer PP-2B.
- Set camera f/stop to 22 (Fig. ##). F/22 is preferred for standard scanning with the current light set up; F/16 is also acceptable. For hard rock cruises, where 360°whole round scanning is required, a larger F/stop number is 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.
Figure ##: 3D standard with MacBeth Color standard.
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4. If the values all look good and there are no streaking issues in the images or other unwanted artifacts, you can click Save and no further adjustments are needed. However if you have determined the doesn't look good, click Cancel and you can proceed to the following section and complete the calibration instructions listed in the Calibration section below.
Calibration (JAI Camera Setup and Image Corrections)
Track Setup
1. Confirm the camera F-stop is set to 22 (Fig. ##). F/22 is preferred for standard scanning with the current light set up; F/16 is also acceptable. For hard rock cruises, where 360°whole round scanning is required, a larger F-stop number is required. See the Advanced SHIL Calibration (in developement) for further information on F-stop.
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Resetting Gains and Corrections
1. Click the Gains-Black-Shade-Flat tab (Fig. 30).
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2. Click the Clear All Gains, Clear Black Gains, Remove Pixel Black Correction, Remove Shading Correction, and Remove Pixel Gain Correction (Fig. ##). You will notice all values in the Master and Black gains go to zero.
Figure 31: Remove the corrections and clear gains.
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The exposure intervals we set relate to how long the camera can pick up values for each color band. Try not to keep the lights on for longer than ~ 20sec 20 sec and then keep them off for ~60 sec. As the lights warm up the RGB values change, particularly the blue value, and change most rapidly in the first minute of the lights warming up. Since the SHIL is often used after being off for a bit, we are trying to calibrate to represent the measuring conditions, as best we can. Right now we do not have a defined procedure for keeping the lights on/off during calibration and thus suggest 20 sec intervals.
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We apply three corrections Pixel Black, Shading and Pixel Gain. Only do the corrections after you have finished adjusting the RGB exposure and gainGain.
Pixel Black Auto Correction: The pixel black level represents extra energy in the camera independent of a light source and is a consistent pattern in the sensor. To correct for this the light source must be turned off, the lens cap put on, and the camera internal correction circuit collects a few lines of data. An average is taken across the line, and pixels are either added to or subtracted from in order for each pixel to have the average value. (Vendor Manual Reference)
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