Find edges in 3-D intensity volume

returns the edges found in the intensity or a binary volume `BW`

= edge3(`V`

,'approxcanny',`thresh`

)`V`

using the approximate Canny method. The approximate Canny method finds edges by
looking for local maxima of the gradient of `V`

.
`edge3`

calculates the gradient using the derivative of a
Gaussian smoothed volume.

For the approximate Canny method, `thresh`

is a two-element
vector in which the first element is the low threshold, and the second element is
the high threshold, `[lowthresh highthresh]`

. If you specify a
scalar for `thresh`

, `edge3`

uses this value for
the high threshold and `0.4*thresh`

for the low threshold.

The approximate Canny method uses two thresholds to detect strong and weak edges, and includes the weak edges in the output only if they are connected to strong edges. This method is more likely than the Sobel method to detect true weak edges.

returns the edges found in the intensity or binary volume `BW`

= edge3(`V`

,'approxcanny',`thresh`

,`sigma`

)`V`

,
where `sigma`

is a scalar that specifies the standard deviation
of the Gaussian smoothing filter. `sigma`

can also be a 1-by-3
vector, `[SigmaX,SigmaY,SigmaZ]`

, specifying different standard
deviations in each direction. For anisotropic volumes that have different scales in
each direction, use multiple sigma values. By default, `sigma`

is
`sqrt(2)`

and is isotropic. `edge3`

chooses
the size of the filter automatically, based on `sigma`

.

accepts an intensity or a binary volume `BW`

= edge3(`V`

,'Sobel',`thresh`

)`V`

and returns a binary
volume `BW`

, that is the same size as `V`

,
with 1s where the function finds edges in `V`

and 0s
elsewhere.

The Sobel method finds edges using the Sobel approximation to the derivative. It
returns edges at those points where the gradient of `V`

is
maximum.

`thresh`

is a scalar that specifies the sensitivity threshold
for the Sobel method. `edge3`

ignores all edges that are not
stronger than `thresh`

.