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Preparing the track system for imaging cores requires adjusting the position of the lights and barcode imager for optimal quality and calibrating the system by adjusting camera settings. The position of the lights and barcode imager, once set, should be stable throughout an expedition. The technical staff will calibrate the camera settings (SHIL: Camera Configuration AUG) and light array (SHIL: Light Array AUG) whenever the camera or light sources have been repositioned or changed.
Setting up the Lights (Section for old lighting system)
Initial light installation and fine adjustment procedures are described in the SHIL: Light Array AUG. For routine operation, follow these steps:
- Rotate the lights to the desired rough angle to the camera (usually ~30° to the camera axis for sediment cores). Fine-tune the light position by observing the camera output using MAX.
- Manually turn on one line light at a time to full power by pressing the "+" button on the light controller until you reach 100%.
- Loosen the brackets on both sides of the light mounts and make small position adjustments until the brightest image is achieved.
- Turn off the light by pressing the "–" button and press Select to enable the other light.
- Repeat Steps 2–4 for the second light.
Calibration
The laboratory technician calibrates the system when needed by adjusting camera settings and analyzing an imaged Kodak Q13 grayscale standard.
Calibration adjustments are performed using an iterative process of imaging a ruler placed crosswise on the track then counting the pixels between millimeter marks, moving the camera up or down, and repeating.*Method based on SHIL Calibration Video. BILL! Please review, correct, and update with screenshots during process!* These lights obtain 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 4-cm 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. While these to 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.
*Method based on Instructions sent by Bill Mills. BILL! Please review, correct, and update!
Safety Concerns
- These lights get hot and can damage or burn surfaces if left stationary and on for over 20-secs. This is not an issue during normal imaging operations and will not heat the core surface at all. BUT during calibration process when the lights are stationary you must use the manual power switch to turn the lights on and off. Do not use the plastic Gray card but use the cardboard instead.
- Never look at the leds directly! Even the reflected light can be painful! When working under the track make sure that the power is off.
- NOTE: if you are concerned with the heat dissipation, you can use our FLIR cameras to confirm that everything is ok.
Glossary of terms:
Gain: a digital camera setting that controls the amplification of the signal from the camera sensor. It should be noted that this amplifies the whole signal, including any associated background noise.
Gamma: a digital camera setting that controls the grayscale reproduced on the image. An image gamma of unity (Figures 3a - 3b) indicates that the camera sensor is precisely reproducing the object gray scale (linear response). A gamma setting much greater than unity results in a silhouetted image in black and white.
White Balance: a camera setting that adjusts the color balance of light the you’re shooting in so that it appears a neutral white, and it’s used to counteract the orange/yellow color of artificial light.
Knee: sets the knee point and slope for video signal compression to prevent over-exposure by limiting signals in high intensity areas of the subject to the dynamic range of your camera, it adjusts the contrast of a picture. Bill Mills: On the SHIL, we tend to not use it. The TIFF correction that gets done on the raw images seems to be good enough.
white.
White Balance: a camera setting that adjusts the color balance of light the you’re shooting in so that it appears a neutral white, and it’s used to counteract the orange/yellow color of artificial light.
Before Starting:
- Color Standard values vary based on the standard and the manufacturer of the standard. Verify the values of the MacBeth Color Standard before starting. Check the grayscale card to determine what the percentage of gray. The target calibration values will vary based on the percentage of gray. Target values depend on the percent grayscale card. Max value 255. If using a 50% grayscale card target red and green value is 127, a 25% grayscale card target value is 64, etc.
- The light array should be calibrated before doing the camera configuration. If installing new lights or a new camera this will be an iterative process adjusting lights and camera.
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- Set camera f/stop to 16.
Camera Corrections
1.Disable the motor that moves the camera. In the IMS control panel select Motion and then Drive Disable from the dropdown menu (Figure 20). The user can now manually move the camera to the desired spot.
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