[vtkusers] Bug in vtkTIFFReader reading multi-paged tiff file

[David Gobbi]

On Thu, Jan 16, 2014 at 2:45 PM, Maarten Beek <beekmaarten at yahoo.com> wrote:
> vtkImageActor::HasTranslucentPolygonalGeometry() seems to want image data of
> type unsigned char and 2 or 4 components in order to do transparency. I'm
> using vtkImageShiftScale to get unsigned char and am working on an algorithm
> to add an alpha component to my one component tiff data. Curious if this
> does the trick.

I strongly suggest that you use vtkImageSliceMapper and vtkImageSlice
to display your images instead of using vtkImageActor.

> I can understand the order is important if one of the actor is opaque, but
> why would this still be important when both are 50% transparent.

That's not how alpha-blending works.  If both images are 50%, then the
frontmost image is displayed at 50%, and the second image gets 25%,
and the background gets the remaining 25%.  That's how translucency
works, both in real-life and in computer graphics.

If you want to blend images 50/50, then the frontmost image should have
50% opacity and the backmost image should have 100% opacity.

> In my app the loading of each image is initiated through a button. I would
> like to create an app which is independent of the order in which the user
> clicks these buttons.

Order is crucial.  That's why I recommend that you use vtkImageStack.
It makes it possible to explicitly set the layer number for each image.

  - David


> On Thursday, January 16, 2014 3:25:11 PM, David Gobbi
> <david.gobbi at gmail.com> wrote:
> Are you using vtk-master (or perhaps a vtk 6.1 release candidate)?
> The TIFF reader had a serious multi-frame bug in older versions.
>
> First, note that the vtkTIFFReader doesn't just give you the raw data
> from the files, it seems to pass it through a lookup table sometimes.
> And I'm not sure exactly how it deals with alpha, and to be honest,
> I wouldn't trust it.
>
> I'm really not sure what you mean when you say "The order of adding
> the actors to the renderer matters, but I try to avoid this by using
> transparency."  The order in which you add images is _crucial_ when
> you are using transparency.
>
> Are you using the vtkImageStack?  It's a class that is designed
> specifically to handle layered rendering of images.
>
>   David
>
>
>
> On Thu, Jan 16, 2014 at 12:40 PM, Maarten Beek <beekmaarten at yahoo.com>
> wrote:
>> Hi David,
>>
>> Is it possible to show all images in a multi-paged tiff transparently?
>>
>> Only when I show the 1st image (page), I see a 2nd 2d image (both are
>> transparent).
>> As soon as I move to another tiff image (page), the 2d image disappears.
>> It
>> returns when I move back to the 1st tiff page.
>>
>> The multi-paged tiff is one component, and I am thinking of an algorithm
>> to
>> add an alpha component, but can hardly believe this would be required...
>>
>> The order of adding the actors to the renderer matters, but I try to avoid
>> this by using transparency.
>>
>> Moving one image in front of the other by changing its z-coordinate using
>> vtkImageActor::SetPosition() doesn't help.
>>
>> Maarten
>>
>>
>>
>> On Friday, November 8, 2013 4:36:06 PM, Maarten Beek
>> <beekmaarten at yahoo.com>
>> wrote:
>> Hi David,
>>
>> Using VTK 6.0.0, sorry ;-)
>>
>> Should I send you the tiff file so you can play with it?
>>
>> Now I seem to have your attention:
>>
>> - How do I display a multi-page tif? I don't seem to see the different
>> images using a vtkImageSlice.
>>
>> - What would be good values for the window and level parameters? I am
>> using
>> window = range[1]-range[0] and level = 0.5*(range[0]+range[1]) which works
>> ok for this multi-page tif, but gets me nowhere when I try to display a
>> drr.
>>
>> Thanks - Maarten
>>
>>
>>
>>
>>
>> On Friday, November 8, 2013 4:23:23 PM, David Gobbi
>> <david.gobbi at gmail.com>
>> wrote:
>> Hi Maarten,
>>
>> Which version of VTK are you using?  I believe that this bug has been
>> fixed in the master branch by a commits in the following topic merge:
>> http://vtk.org/gitweb?p=VTK.git;a=commitdiff;h=7e3d5270
>>
>> It was not fixed in time for VTK 5.10, however.
>>
>>  David
>>
>>
>> On Fri, Nov 8, 2013 at 2:12 PM, Maarten Beek <beekmaarten at yahoo.com>
>> wrote:
>>> Hi all,
>>>
>>> vtkTIFFReader crashed for me while loading a multi-paged tiff file.
>>>
>>> The crash occured in vtkTIFFReader::ReadGenericImage(), because
>>> this->OutputExtent was not set (still NULL).
>>> The scalar type for the image I was loading was unsigned short, so it
>>> happened at line 1368.
>>>
>>> I changed void vtkTIFFReader::ReadVolume(void* buffer) into void
>>> vtkTIFFReader::ReadVolume(void* buffer, int outExt[6]) and added the line
>>> this->outputExtent = outExt.
>>>
>>> This solved my crash.
>>> I am not sure I am on to something, but thought to let you know.
>>>
>>> Maarten
>
>