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1. Confirm the camera F-stop is set to F/16 or F/22 (Figure 15). 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 is required (ie. F/22).
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Color Balancing should be done with the Xrite color checker mini classic (MacBeth) standard version 2019. The grey standard on the top of the track should be the QP card 101 v4 gray scale card. Be sure to use new color standards as some where damaged (faded) by the high temperature of the previous light set up. The calibration using the MacBeth white standard Xrite color checker standard card is described below (note: the QP card v.4 101 method that was implemented in 2020 due to the high temperature of lights is described at end of this User Guide if you need to reference that method).
Color Balancing Camera - MacBeth Xrite Color Checker Classic 2019 Card
Make sure the lens is focused. Use the cm marks on the QP 101 V4 card to focus the lens. If the camera has been moved you will need to adjust the height of the camera using the method described below in Camera Height Adjustment.
1. Put the 3D Calibration Standard in the track. The color square must be oriented as pictured Figure 21.
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Pixel Gain Correction - Flat Method: Each pixel has a different response to a fixed light source. To correct for this non-uniformity a couple lines of data are calculated and the average response of the pixels are calculated. Then each pixel has a correction factor applied to bring all pixels to the average level. The Pixel Gain Correction also corrects for some shading effects and should be done after the shading correction (Note: the order of pixel gain and shading correction is debated, it is suggested to do it in the order above). If color streaking is evident in the image, this correction is needed to remove the unwanted streaking.
Pixel Black Auto Correction
21. Take the lens cap (Figure 26) and place on lens (Figure 27). The lens cap is located in drawer PP-2B. The new light set up makes adding a lens difficult and it has been noted that added the lens may not be needed if the lights are off but I have yet to test that.
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Figure 27. Lens Cap being put on camera
32. Click Pixel Black Auto Correction. The RGB lines in the Profile graph should be uniform (Figure 28).
43. Remove lens cap when finished.
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Figure 28. Grab and Profile after the Pixel Black Correction applied.
Shading Correction
1. Take the heat resistant gray silicone mat and wooden board from the SHIL calibration drawer. Clean off any dust with a piece of tape (Figure 29). Dust will cause unwanted artifacts in the image. The mat must be clean and flat on the track.
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7. Click Lights OFF and wait for temperature to decrease below 35 °C.
Pixel Gain Correction
1. Make sure gray silicone mat is flat.
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3. Click JPEG Corrections tab (Figure 39-3). Adjust the Brightness, Contrast, and Gamma levels (Figure 39-4) to achieve a straight line in the Applied Corrections tab and the ROI Corrected box should have values near 242 for the white square. 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 242. The BCG 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. \
Figure 39. Steps for JPEG Correction illustrated on image. 1. Select JPEG Correction Mode. 2. Select Applied Corrections tab on graph. 3. Select JPEG Correction to see Brightness, Contrast, and Gamma Corrections. 4. Adjust Brightness, Contrast, and Gamma corrections. 6. Check graph for Linear Relationship. 7. Check the boxes in the Color Checker and compare to RGB values in corrected image.
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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. Calibration is complete.
d) Check on Calibrated Computer
Check the final scan:
1. To double check your calibration under the same scanning conditions as the scientists see, scan an image of the 3D standard without the color checker box selected.
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5. Visually examine each file you just preformed to ensure the colors, neutrals, mid-tone and contrast are true to the real values, and that the scan is free from artifacts. Use the eyedropper tool in photoshop to see the values of pixels (Fig. ## Figure needs to be added).
e) Camera Height Adjustment
1. Move the camera so it is just on the edge of the grayscale card at the end on the tray. On this card are mm and cm marks on the edge.
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3. The graph has two cursors, use the mouse and drag one cursor aligning it with the spike. Take the second cursor and do the same with an adjacent spike. Just above the Profile graph there is a control labelled Pixel Delta this value should be between 198 and 202 pixels. If not, adjust the camera up and down refocusing after every move until you get within the range. Warning this can be very tedious!
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f) Calibration with QP 101 V.4 Card
This was a section of the calibration method used for the lights before cooling fans were installed. Color Calibration with the QP 101 V.4 Card.
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Figure 40. Rates and Exposure tab with chronological steps on the screen.
Setting the Line Rate (From Older version of User Guide)
The rules:
- Exposure intervals for the Red, Green and Blue channels is a function of the light intensity of the LEDs.
- Led intensity for the three channels is a function of the LED spectrum. Cold lights 65K are very blue while warm lights 55k are reddish. Neutral light is preferred where RGB are nearly equal but all leds are variable. Generally red is the lowest intensity and will require the longest exposure time. That is why in the above procedure we start with red, but you should always start with lowest intensity channel.
- Intensity is also a function of the F-stop. The smallest F-Top is preferred because it gives the greatest depth of focus but also lowers the intensity.
- Intensity is also a function of how closely coupled the lights are to the core surface but for practical reasons we need to keep a minimum clearance for safe operations.
- Don’t forget to check that all of the lights are evenly illuminated or even on. One led can fail without affecting these other. Don’t ever look at the leds directly!
- Line rate must be greater (20us) than the red, green and blue exposure rates set in the above procedure.
- The shorter the line rates the faster the image can be scanned.
- If you move the track faster than the scan rate you will see dropped lines in your image.
Pre 2019 SHIL Light Array
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