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The laboratory technician calibrates the system when needed by adjusting camera settings and analyzing an imaged XRite Xrite Color Checker Standard Mini standard (MacBeth card). Be sure to use a 2014 or newer version of the Xrite Color checker because the RGB values used for correction uses the values from the newer 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 led mount should be set between 2 and 4cm from the image surface. 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 30-40 °C during calibration. LED's of temperature is located above the camera. During a section scan the temperature ranges between 30-36 °C.
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The first three steps are done using the J AI JAI Camera Setup Utility, the 4th step is done using Image Correction Utility. Before opening the utility it is best to disable Motion Control so that you can move the camera by hand.
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Setting Exposures
BEFORE YOU START
1. Click ) Click the Gains-Black-Shade-Flat tab (Figure 26).
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Figure 26. JAI Camera Setup Window showing the Gains-Black-Shade-Flat tab. The Gains-Black-Shade-Flat tab is outlined in red.
2. ) Click the Clear All Gains, Clear Black Gains, Remove Pixel Black Correction, Remove Shading Correction, and Remove Pixel Gain Correction (Figure 26). You will notice all values in the Master and Black gains go to zero.
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Figure 27. Setting the F Stop on the Camera.
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| title | Correct orientation for the color standard |
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4) Place the 3D Calibration Standard in the track. The color square must be oriented as shown in Figure 28.
Figure 28. Calibration 3D standard with the xrite color checker mini.
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When the camera moves it will receive trigger pulses from the linear encoder. Each trigger pulse will start an exposure the cycle. The encoder will provide 200 pulses for every centimeter of movement; therefore, the speed of the track controls the time between pulse which controls the maximum allowable exposure period. The individual exposure periods for the RGB channels must be completed in this time or lines will be dropped. When setting up the JAI camera we are not moving and not receiving trigger pulses. In this mode we use the line rate trigger (free run) to simulate the encoder trigger period.
When you adjust the Line Trigger Interval you will notice that the Max Image Scan Speed value changes. If you scan faster than this, you will drop lines but you can scan slower with affecting the calibration. When you click Save in the value in the Image Scan Setup window will be updated but you are allowed to change this value but should always be lower not higher. As a general rule we want to stay at 8-cm/s or higher value to maintain core flow in the lab.
After you done a few calibrations you will develop a feel for what is possible with current camera set up but if you just stating we recommend setting the line rate to emulate a scan speed of 8-cm/s. |
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2) Adjust the green exposure until the red/green ratio is near 1.000 (+/-0.005).
3) Adjust the blue exposure until the blue/green ratio is near 1.000 (+/-0.005).
If you cannot get the blue channel to 240, you have several correction options:
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1)The new light set up makes adding a lens cap difficult so it has been decided and tested that the pixel black auto correct correction can be done without the cap (Figure 33). But Ensure the lights are off.
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Ensure the lights are off.
2) With lights off click Pixel Black Auto Correction. The RGB lines in the Profile graph should be uniform (Figure 34).
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