Editing Software Plugins and Codes (section)

====Image differences====
* Load two images
* Select a subregion with the same size in both images
* Select two subregions (Ctrl-Click) and feed them to a Python Calculator.  In the expression field enter this line:
<source lang=python>
inputs[0].CellData.GetArray("AIMData") - inputs[1].CellData.GetArray("AIMData")
</source>
This assumes that the AIM image attaches pixel values to CellData.
* Set 'Array Association = CellData'
* Uncheck 'Copy Arrays'
* Set the Array Name if you want, then hit Apply. 
* To visualize, choose Display->Style->Representation = Slice. Play with XY vs XZ vs YZ views and select a slice of interest. Modify the colormap and mapping of the grayscale values to have a better comparison. 
* Add a second '3D View' in a separate panel and repeat the above for the second image pair. 
* Add the image comparison as a 'custom filter' by selecting the python calculator you just created and choosing Tools->Custom Filter, give a name like 'Compare Images' and click Finish. Select any two images you want to compare and Choose Filter->Alphabetical->Compare Images - done :o)

Here is the end result:

[[Image:ParaviewBeforeVsAfterRegistration.jpg]]