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- 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. For our QP Card v4, the RGB values are 235, 111, and 80.
- Set camera f/stop to 16.
- 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.
Check Calibration
The first step of calibrating is to see if you actually need to by taking an image of the color standard and comparing the observed RGB values and comparing with the expected RGB values.
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7. Move the Camera if necessary to see the QP Card in the image grab window. Draw a green ROI box in the light gray (white) area. Now the Red, Green, and Blue values above the image grab window show the values inside your square. The RGB value of the QP Card v4 in the light gray (white) area is 235. Adjust the Red, Green, and Blue Exposure times until each value is 235. Remember to turn off the lights regularly!
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5. Adjust the Master Black Value until the RGB values are ~40. Qualitatively this is what's been found to produce a nice image. Please note that the RGB value of the QP Card v4 for this square is 80, but this will be corrected for in the tiff/jpeg correction. Remember to turn off the lights regularly!
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After discussion with JAI we learned the order of corrections should be Pixel Black, Shading, and Pixel Gain. Previously our order was Shading, Pixel Gain, and Pixel Black. The order has been updated here. We were also to told to do all exposure and gain adjustments before doing these three camera corrections. This manual has been updated to reflect those changes.
Pixlel Black
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Auto Correction
1.Turn off the lights.
2. Take the lens cap (Figure 33) and place on lens (Figure 34). The lens cap is located in drawer PP-2B.
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Figure 35: Grab and Profile after the Pixel Black Correction applied.
Shading Correction
- Take the silicone gray mat and clean off any dust with a piece of tape (Figure 36A)
- Place the gray silicone mat on the tray bench on top of the QP Card, make sure that it is level and perpendicular to the camera’s axis. The mat should be positioned at the height of the core surface. This is an important step. If the mat is placed closer to the camera your calibration will be off.
- Turn on the lights, with the same method used to turn off the lights, and move the camera over the gray mat.
- Unfocus the lens on the camera just a little bit (Figure 36
- 36B). Look at the Profile graph and rotate the lens’ focus until the RGB lines are smoother, but still have some variation. de-focus the lens until the RGB line on the Profile graph just become smooth and no more (but still variable)
Figure 36A: The Gray silicone mat being cleaned with tape
Figure 3636B: The lens being unfocused.
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. Believe this should happen before setting the exposure or the gain.
45. Now move the camera over the gray silicon mat (Figure 37). The RGB lines should appear “bowed” evenly across profile and centered in the image. If not check the orientation of the gray mat card. This very important!
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5. Click the Shading Correction - Flat Method button. This can take a few seconds, don’t click anything else until it is done. The RGB lines should now be flat (Figure 38).
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Figure 39: Grab and Profile after the Pixel Gain Correction has been applied.
3. Refocus Remove the gray mat and use the QP card to refocus the lens.
4. Click Save. The lights will turn off and the window closes.
Create Correction Curve
Take New Picture
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