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- Physically set the camera at the correct height and focus . See Camera Height and Focusing.
- Next we want to set Set the saturation range for each channel of the CCD while maintaining the white balance between these channels for neutral colors. See Setting Exposures and Setting Gains
- Correct for uneven lighting and pixel flatness. See Shading and Pixel Flat Corrections.
- Calibrate and create a correction LUT for each RGB channel. See Image Calibration.
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The first three steps are done using the JAI Camera Setup Utility. Before opening the utility it is best to disable Motion Cotrol Control so that you can move the camera by hand or open the Motion Widget to control motion with the program. User's choice.
In the IMS control panel select Motion and then Drive Disable from the dropdown menu (Figure 19). 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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Camera Height and Focusing
Setting The goal is to set the across image pixel pitch requires a lot of patience.with a focused camera Warning this can be very tedious.
1) Move the camera so that it is scanning just the centimeter marks on the QP 101. Also, it is important that the QP 101 card is mounted straight so that the scale lines are parallel to the direction of motion.
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On the screen you will see this..
2) On the Profile graph, drag the purple and yellow cursors to the center of two adjacent peaks near the center of the image. These peaks are the centimeter lines in the QP card.
3) Use the graph controls and expand (zoom) the graph horizontally and you should see this…
5) In the expanded view, adjust the cursors so that the are centered in the peak's width (not necessarily the max value).
Checking the focus can be done by obtaining the maximum peak height in the Profile Graph. Adjust the focus back and forth and you notice that the peak rises and falls as you cross the focus point. So after every height adjustment repeat this process for maximum peak height, adjust the cursors and check the Pixel Delta value.
You are ready to begin obtain an in focused pixel pitch of 200-pixels/cm (+/- 1px). You will be repeating the following steps until you reach this goal.
6) Change camera height
7) Focus
8) Adjust cursors
9) Check Pixel Delta
10) Repeat steps 6 through 9 as necessary.
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Be careful how you tighten the clamps holding the camera to the T- Slot. Make sure to tighten with even pressure, if you don't the camera can be offsetand you will see the image in the Grab window shift. The camera attachment method is not ideal and should be replace. After performing this process you need to check the home position. When at the home position, the camera should be scanning the edge of the tray where the section |
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is placed against (red strip). If not, you will need to adjust the home switch on the track until it does. An improperly set home switch will affect the placement of the crop window and potentially the offsets assigned to the RGB values |
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Setting Exposures
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BEFORE YOU START
1. Click the Gains-Black-Shade-Flat tab (Figure 19).
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Figure 18. Setting the F Stop on the Camera.
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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 |
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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. |
CHANGING EXPSOUR VALUES
Now you are ready to start setting the exposures for the RGB channels.
- Turn on the lights
- Click the START GRAB button
- Move the camera over the white square on the ColorChecker standard.
- Use the mouse and draw a ROI (Region of Interest) square with only the white square inside. The RGB values and Ratio values will only be calculated for the pixels inside the ROI.
- Go to the Gains-Black-Shades-Flat tab and click the Clear All Gains and click Clear Black Gains if not already done.
- Go to the Rates and Exposure tab and set the Green Lock to Off
It is helpful to know which RGB channel has the lowest intensity because
Figure 25, Place the cursor in the white square, right-click and draw a rectangle by dragging diagonally. Release the mouse when you have selected most of the white bar. The rectangle (marked in green) should only have the white color and nothing else inside
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It is helpful to know which RGB channel has the lowest intensity because this channel will be the limiting factor when setting exposures. To find this out remove all gains and set identical exposure values for the RGB channels. The intensities will look like Figure XX. If you already know which channel you can skip this step. |
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In this case, it is the blue channel that has the lowest intensity. |
For simplicity well use the blue channel as the weakest.,
- Start with the blue channel, increase the exposure time until its value is between 240-245.
- Adjust the green exposure until the red/green ratio is 1.000 +/-0.005.
- Adjust the blue exposure until the blue/green ratio is 1.000 +/-0.005.
If you cannot get the blue channel tp to 240, you have several correction options:
- Lower the lights for increased illumination intensity
- Open up the f-stop for more light
- Increase the line rate (slower scan speeds) so that you can increase the exposure period
- Use gains to amplify the signals.
Using gains is generally the simplest choose because the other choices are often not practical or desirable. The down side of using gains is that they amplify both signal and electrical noise. Amplifiing Amplifying noise isnot is not good so use gains sapringly as necessarysparingly. In the next section will discuss how to use the gains but remember you will likely move back forth between setting exposures and gains to optimize the camera. It is an iterative process.
Setting Gains
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What is the difference between regular gain and the black gains? Think in terms of a linear calibration where the regular gain sets the slope (multiple) and black gain sets the offset (addition). So changes in the the regular gain value will have little affect on dark colors but changes in the black gain will offset all colors equally. The gains labeled "Master" are applied to all channels while the red and blue apply corrections to only those channels. |
Working with the White Side
1) Open the Gains-Black-Open the Gains-Black-Shades-Flat tab.
2) Adjust the Master Gain until the the weak channel is in the 240-245 range.
3) If the other channels are two high, you can apply negative gains to those channel until get the ratios back to 1 or you can re-adjust the exposures . The later method is preferred.
Once you have initially roughed in the RGB channels for the White ColorCheck square, it time to look at the dark side.
Still in the Gains-Black-Shades-Flat tab, turn off the lights and click Pixel Black Auto Correction. To be honest we are not quite sure what this does and there appears to be no harm if this step is skipped.
Using exposures and gains you have now balanced the White ColorCheck square in the 240-245 range it is time to set the dark response of the camera
preferred.
Once you have initially roughed in the RGB channels for the White ColorCheck square, it time to look at the dark side.
Still in the Gains-Black-Shades-Flat tab, turn off the lights and click Pixel Black Auto Correction. Without light the CCD element will still register a voltage call dark noise. The camera will detect any fixed pattern in the dark noise and correct each pixel to have the same value.
Working With the Dark Side
1) Turn on the lights
2) Click the START GRAB button
3) Move the camera over the white square on the ColorChecker standard.
4) Use the mouse and draw a ROI (Region of Interest) with only the black square inside. The RGB values and Ratio values will only be calculated for the pixels inside the ROI.
5) Adjust the Master Back value unit the Green value is near 15
6) Adjust the Red and Blue Black Gains until the ratio are close to 1 +/- 0.01
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The issue with black is that there is very little energy at this level and noise makes up a significant % of the value. The next issue is that the cameras response from bright to dark objects is non-linear. The ColorChecker value is actually near 50 but do not try to obtain that value by jacking up the gain. It just doesn't work! By convention we aim for ~15. Getting a white balance is also difficult. Once you set the green to 15 move the camera so that you are view the next color just above the dark and use the red and blue black gains to get a good white balance. |
b) Calibration (JAI Camera Setup and Image Corrections)
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Color Balancing should be done with the Xrite X-rite color checker mini classic standard version 2019. The grey standard on the 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). The calibration using the Xrite X-rite color checker standard card is described below (note: the QP card v.4 101 method that was implemented 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).
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2. Click the Pixel Gain Correction - Flat Method button and move the camera slowly back and forth. This averages the pixels and helps eliminate streaking in the image. This will take several seconds, don’t click anything else until it is done. When its done the RGB lines should still be flat and the individual RGB the same, but may not be equal to each other (Figure 32).
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Before Starting:
- Note which version of standard you are using. Each color standard values vary based on the version and the manufacturer of the standard. The XRite Colorchecker 2019 (MacBeth standard, Figure 5) is the preferred card to use for calibration. The program is set up to use the White and Black squares on the XRite Colorchecker (MacBeth standard). On the Xrite color checker standard the RGB values of White and Black are listed here for various illuminants. For illuminant D65 White RGBs are 242, 242 and 236 and and Black RGBs are 49, 49, 50 as of there is discussion that we will use RGBs calculated under illuminant A as it better matches our LED lights. Using illuminant A the RGBs for white is 240, 242, 235 and black is 50, 50, 50. For the QP 101 v4 card, the RGB values are 235, 235, 235 (light grey), 111, 111, 111 (medium grey), and 80, 80, 80 (dark grey) (Figure 6). All SHIL calibration standards are found in drawer PP-2B.
- Obtain the 3D standard (Figure 5) and the gray silicone mat standard from PP-2B.
- Set camera f/stop to either F/16 or F/22 (Figure 7). The camera manufacturer suggested F/22 as the preferred f/stop for scanning with the our light set up however we have found F/16 works well for our section halves and is the most used f/stop for calibration and scanning sections. For hard rock cruises, where 360° whole round scanning is required, a larger f/stop number maybe 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. The camera height should not need to change between expeditions.
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LMUG-SHILUserGuide-020320-1516-374.pdf
