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Figure 18. Setting the F Stop on the Camera.
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Place the 3D Calibration Standard in the track. The color square must be oriented as shown.
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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. |
CHANGING
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EXPOSURE VALUES
Now you are ready to start setting the exposures for the RGB channels.
1) Turn on the lights
2) Click the START GRAB button
3) Move the camera over the white square on the ColorChecker standard.
4)b Use the mouse and draw a ROI (Region of Interest) with only the white square inside. The RGB values and Ratio values will only be calculated for the pixels inside the ROI.
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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
5) Go to the Gains-Black-Shades-Flat tab and click the Clear All Gains and click Clear Black Gains if not already done.
6) Go to the Rates and Exposure tab and set the Green Lock to Off
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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.
In this case, it is the blue channel that has the lowest intensity. |
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If you cannot get the blue channel to 240, you have several correction options:
1) Lower the lights for increased illumination
2) Open up the f-stop for more light
3) Increase the line rate (slower scan speeds) so that you can increase the exposure period
4) Use gains to amplify the signals.
Using gains is generally the simplest choose choice because the other choices options are often not practical or desirable. The down side of using gains is that they amplify both signal and electrical noise. Amplifying noise is not good so use gains sparingly. 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.
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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. 40 is a good starting point.
6) Adjust the Red Black 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. |
Finalizing Exposure and Gain Settings.
You will need go back and repeat the process starting at the section "CHANGING EXPOSURE VALUES" to achieve balanced neutral colors from white to black. But before you do so, this is a good point to first correct Pixel Shading and Pixel Flat.
b) Calibration (JAI Camera Setup and Image Corrections)
Camera and Track Setup
Resetting Gains and Corrections
1. Click the Gains-Black-Shade-Flat tab (Figure 19).
Figure 19. 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 20). You will notice all values in the Master and Black gains go to zero.
Figure 20. Remove the corrections and clear gains.
4. In Master Black field, enter 40. That is a good starting point. We have found the value Master Black of 60 works best for our system's set up.
Color Balancing the Camera
Color Balancing should be done with the X-rite color checker mini classic 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). The calibration using the X-rite 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 - 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. There should be no reason to adjust the height of the camera between expeditions.
1. Put the 3D Calibration Standard in the track. The color square must be oriented as pictured Figure 21.
Figure 21. Color standard in track in correct orientation.
2. Select the tab RATES and EXPOSURE (Figure 22).
Figure 22. Rates and Exposure window, the tab is highlighted in red.
3. On the Green Lock control select OFF (Figure 23). The other exposures are now adjustable.
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Color Balancing the Camera
Color Balancing should be done with the X-rite color checker mini classic 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). The calibration using the X-rite 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 - Xrite Color Checker Classic 2019 Card
Figure 23. Green Lock control highlighted in red and set to off.
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LMUG-SHILUserGuide-020320-1516-374.pdf
