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Clearly visible are the shadows created by both the cap and the meniscus at the liquid level. Although the
juice in this example is colored, such a sharp meniscus will be present even with water-clear liquids. By
measuring both the position of the meniscus and the size of the cap shadow, we can determine if the
bottle is filled and capped properly.
Once again, you can see evidence of the "cosine effect" discussed earlier. There are multiple possible
ways of correcting for this effect. These include:
Storing a brightness contour and dividing each captured pixel level by its contour value (not
•
possible with the AVR firmware due to lack of memory).
Using a telephoto lens and backing off from the subject to narrow the "capture angle" (possible
•
with the TSL1401-DB, but requires a different lens).
Using lighting that's brighter near the image edges than at the center (possible, but sometimes
•
difficult).
Using a floating threshold that approximates the contour when capturing binary images (easiest
•
where practical).
In this example application, we will use the floating threshold method.
© Bueno Systems, Inc. • TSL1401-DB (2009.10.01)
Page 21 of 52
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