[vtkusers] undo changes to binary vtkImageData

[Jonathan Morra]

So I'm in Java and I just realized that GetScalarPointer() isn't mapped to
Java.  Is there an alternative?

On Fri, Jan 28, 2011 at 7:11 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> On Fri, Jan 28, 2011 at 7:45 PM, Jonathan Morra <jonmorra at gmail.com>wrote:
>
>> I have a binary vtkImageData that a user can modify through some tools I
>> provide them.  However, the user has requested an undo stack be made so they
>> can go back through their changes.  In my case, storing a new binary
>> vtkImageData every time the user changes it costs too much memory (these are
>> large 3D volume sets).  Is there a way to store a difference between two
>> binary vtkImageData's?  Ideally I'd like to have just one vtkImageData which
>> is the current image and then a stack of vtkImageDifferences (I made that
>> class up) which are themselves small, but say how to go to either the next
>> or previous state of a binary vtkImageData.
>>
>> Does such a method exist?
>>
>
> No, but it shouldn't be too hard to do this.  You can get a pointer to the
> data by calling GetScalarPointer() on the image data.  The size of this data
> (in bytes) will be product of the Dimensions, the NumberOfScalarComponents,
> and the ScalarSize.
>
> So, you should easily be able to compute a bytewise difference between two
> images.  There's no reason to write a new filter for this, since it's just a
> simple for() loop.  Then, you can use vtkDataCompressor::Compress() to
> compress the diff so that it can be efficiently stored.  By doing everything
> bytewise, you don't have to worry about different datatypes, and you
> shouldn't lose anything in terms of efficiency.
>
> If the image changes in size, then you could store a compressed copy of the
> full image rather than dealing with the difficulty of diffing images of
> different sizes.
>
> I hope this helps.
>
>   - David
>
>
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