VTK/Threaded Image Algorithms: Difference between revisions
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== Review of Streaming Pipeline == | == Review of Streaming Pipeline == | ||
The job of a vtkAlgorithm is to perform some operation upon some data (specifically, upon some data encapsulated in a vtkDataObject). | The job of a vtkAlgorithm is to perform some operation upon some data (specifically, upon some data encapsulated in a vtkDataObject). One important aspect of VTK's streaming pipeline is that the vtkDataObject that the algorithm operates on might be one part of a larger data set. For example, a vtkImageData object might only contain a few slices of a large stack of image slices. | ||
The portion of a data set that is contained within one vtkImageData object is described by the ''Extent'' array, which provides a (first, last) index for each of the three dimensions: | |||
== Splitting the | Extent = { first_idx_x, last_idx_x, first_idx_y, last_idx_y, first_idx_z, last_idx_z } | ||
The pipeline tells the algorithm two important pieces of information: | |||
# How large the entire data set is (the '''WHOLE_EXTENT'''). | |||
# What part of the data set the output vtkImageData object should contain after the algorithm runs (the '''UPDATE_EXTENT'''). | |||
== Splitting the UPDATE_EXTENT among threads == | |||
The algorithm is responsible for producing a vtkImageData object whose size and position within the entire data set described by the '''UPDATE_EXTENT'''. But wait, what if we want to divide the work among several threads? Then the '''UPDATE_EXTENT''' must be broken into several chunks, each of which is also an ''extent''. For example, let's say that the update extent is { <span style="color:#800000">128</span>, <span style="color:#800000">255</span>, <span style="color:#008000">0</span>, <span style="color:#008000">255</span>, <span style="color:#0000D0">1</span>, <span style="color:#8000D0">100</span> }: | |||
UPDATE_EXTENT: { 128, 255, 0, 255, 1, 100 } | |||
Thread 1 extent: { 128, 255, 0, 255, 1, 25 } | |||
Thread 2 extent: { 128, 255, 0, 255, 26, 50 } | |||
Thread 3 extent: { 128, 255, 0, 255, 51, 75 } | |||
Thread 4 extent: { 128, 255, 0, 255, 76, 100 } | |||
In this example, the data has been divided along the Z direction. | |||
== Multithreading == | == Multithreading == | ||
Revision as of 04:29, 17 March 2015
Review of Streaming Pipeline
The job of a vtkAlgorithm is to perform some operation upon some data (specifically, upon some data encapsulated in a vtkDataObject). One important aspect of VTK's streaming pipeline is that the vtkDataObject that the algorithm operates on might be one part of a larger data set. For example, a vtkImageData object might only contain a few slices of a large stack of image slices.
The portion of a data set that is contained within one vtkImageData object is described by the Extent array, which provides a (first, last) index for each of the three dimensions:
Extent = { first_idx_x, last_idx_x, first_idx_y, last_idx_y, first_idx_z, last_idx_z }
The pipeline tells the algorithm two important pieces of information:
- How large the entire data set is (the WHOLE_EXTENT).
- What part of the data set the output vtkImageData object should contain after the algorithm runs (the UPDATE_EXTENT).
Splitting the UPDATE_EXTENT among threads
The algorithm is responsible for producing a vtkImageData object whose size and position within the entire data set described by the UPDATE_EXTENT. But wait, what if we want to divide the work among several threads? Then the UPDATE_EXTENT must be broken into several chunks, each of which is also an extent. For example, let's say that the update extent is { 128, 255, 0, 255, 1, 100 }:
UPDATE_EXTENT: { 128, 255, 0, 255, 1, 100 }
Thread 1 extent: { 128, 255, 0, 255, 1, 25 }
Thread 2 extent: { 128, 255, 0, 255, 26, 50 }
Thread 3 extent: { 128, 255, 0, 255, 51, 75 }
Thread 4 extent: { 128, 255, 0, 255, 76, 100 }
In this example, the data has been divided along the Z direction.
