Environmental Engineering Reference
In-Depth Information
CCD
progressive
scan camera
High
magnification
lens
Mounting holes for the
stablizing brackets
Low
magnification
lens
Stablizing
brackets
Multi-port
flow through
cell
Outlet
Inlet
Extension
tubes
Access ports for backlighting
Sample inlet
(a)
(b)
Fig. 1.12
Suspended-sediment digital optic-imaging components. (a) Cameras atop encased lenses with extension tubes and
encased fl ow-through cell (fi ber-optic cable not shown). (b) Multi-port fl ow-through cell (patent pending).
may be an upper SSC-measurement limit, any such
value is still to be determined.
Inherent complexities involved with imaging indi-
vidual particles in a liquid medium can create impedi-
ments to extracting usable information from the
binary images, which usually contain fewer textural
details than appear in the original image. Despite
some loss of detail in the image, the derived solid-
phase images, referred to as “blobs,” are better
suited for analysis by the imaging software - particu-
larly for conducting discrete analyses such as
particle-edge detection and for computing the size
and shape characteristics of individual sediment
particles in the fi nal analysis.
The fl ow-through cell design results in effective
dispersion of most particles to render most particle
boundaries distinguishable. In the event of incom-
plete particle dispersion and (or) large SSCs that
increase the incidence of imaged-particle overlap,
the software uses interpretations based on image
normalization, segmentation, and other imaging
analysis tools to aid in identifying individual
particles.
Balance in contrast is essential for obtaining useful
images of sediment particles. As part of the prototype
lens assembly, two in-line polarized fi lters are ori-
ented 50-70 ° from cross-polarization between the
Fig. 1.13
A morphologically transformed image of a
water-sediment mixture illuminated by cross-polarization.
Each sediment particle and a possible aggregate appearing
as a single particle are numbered.
application. Once an image of the water-sediment
mixture in the fl ow-through cell is captured, mor-
phological transformations (successions of pixel-
level image processing) are conducted. The fi nal
image is used to extract discrete particle information
such as maximum and minimum lengths, shape and
area (Kindratenko 1997) (Fig. 1.13). Although there
