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3. The graph has two cursors, use the mouse and drag one cursor aligning it with the spike. Take the second cursor and do the same with an adjacent spike. Just above the Profile graph there is a control labelled Pixel Delta this value should be between 198 and 202 pixels. If not, adjust the camera up and down refocusing after every move until you get within the range. Warning this can be very tedious!
d) Calibration with QP 101 V.4 Card
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METHOD USED FOR HIGH TEMP LIGHTS Color Calibration with the QP 101 V.4 Card. Adjust Exposure (Achieving White Balance by Shutter Correction)
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- Exposure intervals for the Red, Green and Blue channels is a function of the light intensity of the LEDs.
- Led intensity for the three channels is a function of the LED spectrum. Cold lights 65K are very blue while warm lights 55k are reddish. Neutral light is preferred where RGB are nearly equal but all leds are variable. Generally red is the lowest intensity and will require the longest exposure time. That is why in the above procedure we start with red, but you should always start with lowest intensity channel.
- Intensity is also a function of the F-stop. The smallest F-Top is preferred because it gives the greatest depth of focus but also lowers the intensity.
- Intensity is also a function of how closely coupled the lights are to the core surface but for practical reasons we need to keep a minimum clearance for safe operations.
- Don’t forget to check that all of the lights are evenly illuminated or even on. One led can fail without affecting these other. Don’t ever look at the leds directly!
- Line rate must be greater (20us) than the red, green and blue exposure rates set in the above procedure.
- The shorter the line rates the faster the image can be scanned.
- If you move the track faster than the scan rate you will see dropped lines in your image.
Pre 2019 SHIL Light Array
Please see the Pre 2019 SHIL Light Array info here.
C. Set Measurement Parameters
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A link to the Excel Spreadsheet of RGB values calculated from L*a*b* for the Xrite Mini Color Checker is here. L*a*b* was obtained from xrite.com.
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