Re: can i draw cylinders!

Posted by Gabriel Landini on Oct 24, 2006; 10:27am
URL: http://imagej.273.s1.nabble.com/can-i-draw-cylinders-tp3701211p3701214.html

On Tuesday 24 October 2006 09:58, Christophe Leterrier wrote:
> What would be needed is a way to draw a line (wathever the type) and
> having some kind of "expand" command to generate a thick snake from that
>line, that would then be considered as a surface ROI, not a linear one.

You can generate a thick line from a set of coordinates by painting filled
disks with centre at each coordinate of your freehand line.
This is almost the same as doing morphological dilation of the line with
circular kernels.

You can also obtain a similar result by drawing the line on the image and then
calculating the Euclidean distance transform of the background. The
transformed image can then be thresholded to obtain the thickened line by
so-many pixels.

The problem you will face is that the length of the thickened line (if it is
irregular) becomes shorter with the increased thickening (i.e. with
increasing thickness the small detail is erased at a rate related to the
fractal dimension of the line). This is a known effect and typical of
irregular/fractal objects, but you need to know the fractal dimension
beforehand to do the correction (!). An iterative solution has been described
in:

Flook AG. The use of the dilation logic on the quantimet to achieve fractal
dimension characterisation of textured and structured profiles. Powder
Technology 1978;21:295-298.

Flook AG. Fractal dimensions: their evaluation and their significance in
stereological measurements. Acta Stereol, Proc 3rd Eur Symp Stereol 2nd Part
1982;:/79-87.

I hope it helps.

Gabriel