Layer: Layer
In neuroim: Data Structures and Handling for Neuroimaging Data

create a Layer object

1 2	Layer(vol, colorMap = gray((0:255)/255, alpha = 1), thresh = c(0, 0), axis = 3, zero.col = "#000000", alpha = 1)

`vol`	volume instance of `BrainVolume`
`colorMap`	a lookup table defining mapping from image intensity values to colors.
`thresh`	a range (min,max) defining the threshold window for determining image opacity.
`axis`	the axis index of the axis perpendicular to the xy plane (options: 1,2,3; default is 3)
`zero.col`	the color used when the value is zero.
`alpha`	transparency multiplier, vlaue between 0 and 1.