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IDProjectCategoryView StatusLast Update
0002477Slicer4Core: GUIpublic2013-07-08 10:21
ReportersbillinAssigned Topieper 
Status assignedResolutionopen 
Product VersionSlicer 4.1.0 
Target VersionFixed in Version 
Summary0002477: Background and Foreground Images Crop Each Other in Slice Views

If I have two images that partially overlap and I want to observe their overlap in the Slice Viewers, I set one image to foreground and the other to background using the control widget on the Slice Viewer.

If the blend setting is "Alpha Blend", then the foreground image is cropped to the extent of the background image. If the blend setting is "Reverse Alpha Blend" then the situation is reversed (the background image is cropped to the extents of the foreground image).

Because of this problem, I often have to go back and forth with swapping my foreground and background images in order to see the entire scene, since neither one fully contain the other.

I am attaching two example images for demonstrating this. The effect is easiest to see when adjusting the windowing so the boundaries of each image appear as grey.

Additional Information

I don't see any problem when using the "Add" blend setting.

With "Subtract" for the blend setting, all area covered by the background image is completely black and the foreground portion not covered by the background appears normal. It is surprising that all the background region is black, since my two images are of the same object, but with a translation applied between them so that they do not align with each other. So this seems to be another bug as well.

Slicer Version: R20725
OS: Windows 7

TagsNo tags attached.


2012-09-05 13:17


Example.mhd (330 bytes)

2012-09-05 13:17


Example.zraw (195,853 bytes)

2012-09-05 13:17


Example_Tx50Ty75.mhd (341 bytes)

2012-09-05 13:17


Example_Tx50Ty75.zraw (195,853 bytes)


2012-09-21 14:24

administrator   ~0006168

I can see the benefit of being able to do the alpha blending and see both volumes, but it doesn't look like an easy change. The current behavior existed in slicer3 also, so I'm classifying this as a feature request instead of a bug.

The workaround of using the Add mode seems to make sense to me for situations where the volumes are very far apart and you want see both. When they they are closer to overlapping, then alpha blend makes more sense.

To fix this we'd need a custom filter that combines functionality from vtkImageBlend and vtkImageMathematics where the alpha channel is created from an OR of the inputs and the blend operation applies for the color.

Issue History

Date Modified Username Field Change
2012-09-05 13:17 sbillin New Issue
2012-09-05 13:17 sbillin Status new => assigned
2012-09-05 13:17 sbillin Assigned To => kikinis
2012-09-05 13:17 sbillin File Added: Example.mhd
2012-09-05 13:17 sbillin File Added: Example.zraw
2012-09-05 13:17 sbillin File Added: Example_Tx50Ty75.mhd
2012-09-05 13:17 sbillin File Added: Example_Tx50Ty75.zraw
2012-09-05 15:53 kikinis Assigned To kikinis => pieper
2012-09-19 04:18 pieper Target Version => Slicer 4.2.0 - coming release
2012-09-21 14:24 pieper Note Added: 0006168
2012-09-21 14:24 pieper Severity minor => feature
2012-09-21 14:24 pieper Target Version Slicer 4.2.0 - coming release => Slicer 4.3.0
2013-07-08 10:21 pieper Target Version Slicer 4.3.0 =>