# tend-evq - Man Page

quantize directions of diffusion

## Synopsis

**tend evq** [**-c** <*evec index*>] **-a** <*aniso*> [**-ns**] [**-i** <*nin*>] [**-o** <*nout*>]

## Description

Quantize directions of diffusion. Because VTK doesn’t do multi-dimensional colormaps, we have to quantize directions of diffusion (usually just the principal eigenvector) in order to create the usual XYZ<->RGB coloring. Because eigenvector directions are poorly defined in regions of low anisotropy, the length of the vector (pre-quantization) is modulated by anisotropy, requiring the selection of some anisotropy metric.

## Options

- -c <
*evec index*> Which eigenvector should be quantized:

“

**0**” for the direction of fastest diffusion (eigenvector associated with largest eigenvalue), “**1**” or “**2**” for other two eigenvectors (associated with middle and smallest eigenvalue) (*int*); default: “**0**”- -a <
*aniso*> Which anisotropy metric to scale the eigenvector with. All the Westin metrics come in two versions. Currently supported:

- “
**cl1**”, “**cl2**”: Westin’s linear - “
**cp1**”, “**cp2**”: Westin’s planar - “
**ca1**”, “**ca2**”: Westin’s linear + planar - “
**cs1**”, “**cs2**”: Westin’s spherical - “
**ct1**”, “**ct2**”: GK’s anisotropy type (cp/ca) - “
**ra**”: Basser/Pierpaoli relative anisotropy/sqrt(2) - “
**fa**”: Basser/Pierpaoli fractional anisotropy - “
**vf**”: volume fraction = 1-(Basser/Pierpaoli volume ratio) - “
**tr**”: trace

- “
- -ns
Don’t attenuate the color by anisotropy. By default (not using this option), regions with low or no anisotropy are very dark colors or black

- -i <
*nin*> input diffusion tensor volume; default: “

**-**”- -o <
*nout*> output image (floating point) (

*string*) default: “**-**”