[vtkusers] bit wise operations for vtkImageData

[David Gobbi]

In python it is possible to access the VTK data arrays directly via
python's buffer interface, so that's what I use when I want to quickly
move pixel data back and forth from python to VTK.  It allows me to
use a VTK array (including the one that the image uses to store its
pixels) as if it was a native python array.

I have a feeling that the only way you will be able to rapidly do VTK
pixel operations of any kind from Java, is if someone adds a similar
feature to the Java wrappers.

 - David


On Fri, Mar 25, 2011 at 1:31 PM, Jonathan Morra <jonmorra at gmail.com> wrote:
> Your understanding is correct, however I cannot
> use GetScalarComponentAsDouble and SetScalarComponentAsDouble because they
> are way too slow in Java.  Do you have any other suggestions for how to do
> this or will I have to write it myself in C++?
>
> On Fri, Mar 25, 2011 at 12:29 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>
>> Hi Jonathan,
>>
>> If I understand correctly, you have several binary images with exactly
>> the same dimensions.  And you want to collapse them into a single
>> image, by storing a bitfield in the pixels of that image.  So:
>>
>> To set bit "i" in pixel "xyz" (C++ code):
>> int a = int(image.GetScalarComponentAsDouble(x, y, z, 0));
>> a |= (1 << i);
>> image.SetScalarComponentAsDouble(x, y, z, a);
>>
>> To clear bit "i" in pixel "xyz":
>> int a = int(image.GetScalarComponentAsDouble(x, y, z, 0));
>> a &= ~(1 << i);
>> image.SetScalarComponentAsDouble(x, y, z, a);
>>
>> To test bit "i" in pixel "xyz":
>> int a = int(image.GetScalarComponentAsDouble(x, y, z, 0));
>> return ((a >> i) & 1);
>>
>> But I'm not sure if this is what you are trying to do.  I didn't fully
>> understand your pseudocode.
>>
>>  - David
>>
>>
>>
>> On Fri, Mar 25, 2011 at 1:08 PM, Jonathan Morra <jonmorra at gmail.com>
>> wrote:
>> > I'm in Java and storing a large number of binary vtkImageData's.  I know
>> > this is inefficient, and am searching for a better way to store them.
>> >  Right
>> > now I have a hash of the vtkImageData's and a get/put function.
>> >  Basically I
>> > want to mimic this get/put but with better storage.  I was thinking one
>> > way
>> > to do this is to use bitwise logical operations to store the information
>> > in
>> > the binary masks.  For instance, if we have 2 binary images, then we
>> > could
>> > store that information in 1 vtkImageData using the following pseudo
>> > code.
>> > private static final int IMAGE1_BIT_CHANNEL = 0;
>> > private static final int IMAGE2_BIT_CHANNEL = 1;
>> > private vtkImageData storedImage;
>> > vtkImageData get(String image)  {
>> >     int channel = image eq "image1" ? IMAGE1_BIT_CHANNEL :
>> > IMAGE2_BIT_CHANNEL;
>> >     vtkImageData return = new vtkImageData();
>> >     foreach (pixel in storedImage)
>> >         if (pixel at bit channel)
>> >             return[pixel] = 1;
>> >         else
>> >             return[pixel] = 0;
>> >     return return;
>> > }
>> > void put(String image, vtkImageData binaryImage) {
>> >     int channel = image eq "image1" ? IMAGE1_BIT_CHANNEL :
>> > IMAGE2_BIT_CHANNEL;
>> >     foreach (pixel in binaryImage)
>> >         if (pixel)
>> >             storedImage at bit in channel = 1;
>> >         else
>> >             storedImage at bit in channel = 0;
>> > }
>> > This could be extended easily for 8 channels for a char image for
>> > instance.
>> >  This operation would have to be very fast though cause it is done often
>> > on
>> > the UI thread.
>> > 1.  Is there a way to do this in VTK with Java?
>> > 2.  Is this the best scheme for accomplishing my goal?
>> > 3.  Is there a better scheme for doing this?
>> > Thanks.
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