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- 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 MacBeth standard the RGB values of White and Black are listed here. White RGBs are 242, 242 and 236 and black RGBs are 49, 49, 50. For the QP 101 v4 card, the RGB values are 235 (light grey), 111 (medium grey), and 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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3. Remove lens cap when finished.
Figure 28.
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Pixel Black Correction applied.
Shading Correction
1. Take the heat resistant gray silicone mat and wooden board from the SHIL calibration drawer. Clean off any dust with a piece of tape (Figure 29). Dust will cause unwanted artifacts in the image. The mat must be clean and flat on the track.
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3. Click Lights On, and move the camera over the gray mat.
4. This step Note for Tech: previously we defocused the lens to preform the Shading correction. That is no longer needed (info with strikethrough) because the silicone matting is homogenous. The previous material used had a mottle effect and thus defocusing was required to provide an even surface. If you find that defocusing is still valid please make a note here. Defocus the lens on the camera just a little bit (Figure XX). Look at the Profile graph and slightly rotate the lens’ focus until the RGB lines are smoother, but still have some variation. mat is even in color/texture.
Figure 29. The Gray silicone mat being cleaned with tape.
Figure XX: The lens being unfocused.
5. The RGB lines should appear “bowed” evenly across profile and centered in the image (Figure 30). If not check the orientation of the gray mat, it needs to be flat and perpendicular to the camera. This very important!. A wooden holder was designed to hold the mat, it should be in the SHIL calibration drawer.
Figure 30. Grayscale card corresponding RGB Profile visible.
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