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SKIING WITH LAMBERT  --  SNOW, ILLUMINATION AND MACHINE VISION  (continued)


5. Application: How to Illuminate Machine Vision (continued)


5.5 Scanning 'Natural' 3-D Scenes
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Key words:

shadows | collimated | overcast-sky | confocal



In three-dimensional scenes, you'd better know whether you want SHADOWS to be visible or not.

You can choose:

* Either COLLIMATED illumination (fig. 5_4_a or 5_4_b in para. 5.4), achieving deep-black shadows and thus, a pseudo-stereoscopic appearance;

* or OVERCAST-SKY illumination (fig. 5_2_a in para. 5.2), where details are less obscured by shadows;

* or CONFOCAL illumination (fig. 5_5_a), where no shadows at all appear in the image.
On the other hand, a CONFOCALly illuminated image might look somewhat "flat", and with glossy plane objects, a "hot spot" can shine up in the image center.

fig. 5_5_a: confocal illumination; 15 kByte

The same figure is shown animated at the bottom of this page.

In the following table, some benefits and drawbacks of confocal illumination are listed:

ADVANTAGE DISADVANTAGE
no object obscured by shadow pseudo-stereoscopic impression is lost
between scanner and object, beam of minimum cross-section area even the least quantity of dirt on front lens severely impairs image contrast
compact one-piece scanner unit field lens, beam splitter, and light trap necessary
no illumination spilled  outside of  field of view double-pass through beamsplitter reduces illumination efficiency to 1/4




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Last modified Jul. 21st, 2009


fig. 5_5_a: confocal illumination; 15 kByte