Add qt to vtk image

[lassoan]

Add utility function to convert Qt image to VTK image and fix a few Python wrappings.

[finetjul]

A QImage may not be RGBA, it has multiple pixel formats.

[finetjul]

Alternatively, you may want to use vtkQImageToImageSource

[lassoan]

I've tried to use vtkQImageToImageSource first. First problem was that the filter was not wrapped by VTK's Python wrapper. I've tried to add a wrapping around it from CTK, but it turned out it was not included in VTK_LIBRARIES. Instead of blindly adding one more dependency, I had a look at the vtkQImageToImageSource implementation and realized that the filter is overcomplicated and the operation can be implemented in a few lines of code and so it is not worth using vtkQImageToImageSource.

[finetjul]

Fair enough

[lassoan]

QImage may not be RGBA, it has multiple pixel formats.

We call inputQImage.convertToFormat(QImage::Format_RGBA8888), to get an RGBA image.

[finetjul]

QImage may not be RGBA, it has multiple pixel formats.

We call inputQImage.convertToFormat(QImage::Format_RGBA8888), to get an RGBA image.
Yep, I saw that afterwards.

That's good with me then.

[pieper]

Do you plan to replace the corresponding code that's already in Slicer?

https://github.com/Slicer/Slicer/blob/a02f79c7c788708a3dccfeb9ff4df76b6a5868be/Libs/MRML/Widgets/qMRMLUtils.cxx#L151-L205

[lassoan]

Do you plan to replace the corresponding code that's already in Slicer?

https://github.com/Slicer/Slicer/blob/a02f79c7c788708a3dccfeb9ff4df76b6a5868be/Libs/MRML/Widgets/qMRMLUtils.cxx#L151-L205

I've added this new function because I did not find it in Slicer (the closest was the one in CTK, which only provided conversion in the other direction).

I think it makes sense to have the feature available at the lowest-level library (and use that in higher-level libraries). So, I would move the best implementation of the converters to CTK and use that from qMRMLUtils.

[lassoan]

Thanks for the reviews. I've consolidated with the implementations in Slicer, added a test, and merged.