[Insight-users] Please give me a hand in understanding pipeline

[zhao]

Hi Luis,

	By reading the source code of WaterShedSegmentation example, I got a taste of the pipeline architecture used in ITK. In this example, there are three filters (except for image read and write filters): Anisotropic Diffusion Filter, Gradient Magnitude Filter, and Watershed Segmentation Filter. I know the output of one filter is the input of it's subsequent filter, and thus a processing pipeline is constructed. It seems that it's the Write() member function of ImageFileWriter object that triggers the whole processing procedure. Now, I got two question to ask:
	
	(1) How does the later Filter trigger the former Filter's execution? ( e.g. Watershed trigers Gradient, and Gradient triggers Diffusion ).
	(2) How does a Process Object (i.e. a filter) begin it's own processing? (e.g. I think the processing subroutine of GradientMagnitudeImageFilter should be ThreadedGenerateData, but I can't find explicitly where GradientMagnitudeImageFilter evoke it. )

	Maybe it's too complex to give a clear explanation. Any reply will be appreciated. Thanks in advance!!

Zhao
    

Zhao ChenGuang
P.O.Box:010,
Dept. BME
Shanghai Jiao Tong University,
1954# Hua Shan Road,
Shanghai,P.R.China,
200030