[vtkusers] "zoom in" in VTK Image viewer when displaying CT images

[Prashanth]

David,

Thanks for the immediate response. Your suggestion works.

I stopped debugging ITK-SNAP at glScalef and assumed that it was the
command responsible for displaying texture. After I read your email, I
looked further and ITK-SNAP does use texture mapping and the default is set
to 'nearest neighbor'. I changed that to 'Linear' and the display (after
zooming in) is similar to VTK.

Thanks again
Prashanth


On Sun, Jun 7, 2015 at 7:55 AM, David Gobbi <david.gobbi at gmail.com> wrote:

> Hi Prashanth,
>
> VTK uses glLoadMatrix and glMultMatrix to load the view transforms, but
> whether these are used, versus glScale, has no impact on image quality.
>
> Instead, image display quality is a result of what filtering is used when
> drawing the image.  When image interpolation is turned on in VTK (which is
> the default) the following OpenGL calls are made as part of the texture
> display pipeline:
>
>     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
>     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
>
> If ITK-SNAP uses textures to display images, these functions should also
> work there.
>
>  - David
>
> * Note: VTK is rapidly moving to a new OpenGL implementation where shader
> programs are used, rather than calls to glLoadMatrix and glTexParameter.
>
> On Sun, Jun 7, 2015 at 8:13 AM, Prashanth <prashanth.dumpuri at gmail.com>
> wrote:
>
>> All,
>>
>> I recently discovered ITK-SNAP and have noticed that ITK-SNAP produces a
>> pixelated image (poor quality image) when zooming in the 2D image views.
>> I'm just doing a 2x zoom in ITK-SNAP but the image looks really pixelated
>> after zooming in.
>>
>> In my opinion VTK Image viewer produces better looking images. My CT
>> image is of size 832 x 832 x 265 (0.8mm slice thickness). So, it's not lack
>> of data in the input image that's causing pixelated displays. I don't know
>> how VTK handles zooming but as I understand it, glScalef is the function in
>> ITK-SNAP handling zoom.
>>
>> How does VTK handle 'zoom in' ? Is there something I can do to improve
>> the quality in ITK-SNAP?
>>
>> P.S. I have asked ITK-SNAP a similar question about 'zooming in' and
>> glScalef. I'm posting here because I would like to know how VTK handles
>> 'zooming in' and also in my limited experience with ITK-SNAP, the response
>> time in VTK users mailing list is quicker.
>>
>> Thanks
>> Prashanth
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://public.kitware.com/pipermail/vtkusers/attachments/20150607/52277c9a/attachment.html>