[vtkusers] How to change pixel color?
Romuald BERTRAND
beromuald at wanadoo.fr
Fri May 23 05:40:33 EDT 2008
Hi Mark, thanks for your help,
I have tried this little algorithm :
//Point on the scalars
unsigned short* pPix = (unsigned short*)ima->GetScalarPointer();
//Search for the maximum
unsigned short max(0);
for( int i=0; i<dimX*dimY; i++ )
{
if( pPix[i] > max )
max = pPix[i];
}
//Creating LUT
vtkLookupTable* LUT = vtkLookupTable::New();
LUT->Allocate(65536);
LUT->SetTableValue(max+1, 0, 255, 0); //RGB, A=1.0
LUT->Build();
//Creating iterator for the list (pN3 contains points coordinates)
list<pN3>::iterator it;
for( it = liste.begin(); it != liste.end(); it++ )
{
double ptSeg[3];
ptSeg[0] = (*it).x;
ptSeg[1] = (*it).y;
ptSeg[2] = (*it).z;
//Search for point index
int nVolIdx = ima->FindPoint(ptSeg);
pPix[nVolIdx] = max+1;
}
//PROBLEM HERE
vtkActorCollection* Collec = pRenderer->GetActors();
Collec->InitTraversal();
Collec->GetNextItem()->GetMapper()->SetLookupTable(LUT);
Refresh();
But when Collec->GetNextItem()->GetMapper()->SetLookupTable(LUT); the programm crashes. Do you know why? I made an error?
Thanks for your help,
Bye
Romu
> Message du 22/05/08 20:24
> De : "Mark Wyszomierski"
> A : "Romuald BERTRAND"
> Copie à : yenanqu at scs.fsu.edu, vtkusers at vtk.org
> Objet : Re: [vtkusers] How to change pixel color?
>
> Yeah that's tricky because converting your original greyscale data
> into three component color data implies you're only going to be using
> 255 possible grey values, whereas your original grey data might be in
> the 16 bit range etc. So, what are you going to do with a grey value
> of say 3000? This problem occurs even when you're viewing a greyscale
> image because you need to map the grey values into the range that the
> monitor can display. I guess this is what window/leveling is for, so
> you're determining some window/scale to remap all those really big
> gray values for the user. Can anyone verify that?
>
> This isn't a good recommendation, but it's something I hacked together
> just to get a temporary visualization going. If your greyscale data is
> being stored in unsigned shorts let's say, you can iterate over all
> the pixel data and find the max value used. For the images I worked
> with, this was rarely near the unsigned short max value, it was
> usually 20,000 let's say. Then if I wanted to display green pixels in
> the volume, I would use a lookup table and add points like 20001 =
> (0,255,0), 20002 = (255,0,0) and so on. You're sure your greyscale
> data never uses those values. Then you replace the voxels of interest
> with those appropriate lookup table values. When you hand the volume +
> LUT to VTK, you'll see the voxels in the colors you chose.
>
> There are problems with doing that of course. One is that your LUT
> will always have to be dynamically created which is kind of annoying.
> You're also overwriting voxel values in the source volume, so you need
> to keep a reference to a copy of the ones you overwrite if you want to
> 'remember' the original greyscale values. The list goes on. But it
> works and maybe it can give you some ideas.
>
> I'm sure other people have done this and they probably have better suggestions,
>
> Mark
>
>
> On 5/22/08, Romuald BERTRAND wrote:
> > Ok, pPix = (unsigned char*)id->GetScalarPointer(); works for me.
> >
> > But I have a problem : I display a grey image (1 component) and I want to
> > change few pixels in green (for example), I don't know how can I do this.
> > The grey image has 1 scalar component, and I need to transform its to 3
> > components, and it takes a lot of time, and it's not very interactiv.
> >
> > Someone know can I do my task?
> >
> > Thanks a lot for answers,
> >
> > Romu
> >
> > PS : yenan, make sure you change just one component if you have a grey
> > image, and change 3 components if you have a rgb image.
> >
> >
> >
> >
> >> Message du 19/05/08 20:54
> >> De : yenanqu at scs.fsu.edu
> >> A : "Romuald BERTRAND"
> >> Copie à : "Mark Wyszomierski" , vtkusers at vtk.org
> >> Objet : Re: [vtkusers] How to change pixel color?
> >>
> >> No, I am still trying it. if you have other way to or could make it
> >> work, please, please let me know.
> >>
> >> Yenan
> >>
> >> Quoting Romuald BERTRAND :
> >>
> >> > Hi,
> >> >
> >> > Thanks for your answers.
> >> >
> >> > I have tried but pPix = (unsigned char*)id->GetScalarPointer();
> >> > doesn't work for me.
> >> >
> >> > when I change the components, nothing change, and after I have
> >> > display the array and I have seen it is null.
> >> > Know you why?
> >> >
> >> > Yenan: Have you arrived to manipulate it correctly?
> >> >
> >> > Thanks
> >> >
> >> >
> >> >
> >> >> Message du 16/05/08 21:35
> >> >> De : "Mark Wyszomierski"
> >> >> A : yenanqu at scs.fsu.edu
> >> >> Copie à : "Romuald BERTRAND" , vtkusers at vtk.org
> >> >> Objet : Re: [vtkusers] How to change pixel color?
> >> >>
> >> >> >> pPix = (unsigned char*)id->GetScalarPointer();
> >> >>
> >> >> That should work, I've used it many times for instance in this project:
> >> >>
> >> >>
> >> >> http://devsample.org/index.php?option=com_content&task=view&id=48&Itemid=27
> >> >>
> >> >> I show the value of the pixel that the mouse is over. Maybe there's
> >> >> something else going on in your pipeline?
> >> >>
> >> >> Mark
> >> >>
> >> >>
> >> >>
> >> >> On 5/16/08, yenanqu at scs.fsu.edu wrote:
> >> >> > How to get pointer from vtkImageData is the hardest thing,which I
> >> >> > still can not make it.
> >> >> >
> >> >> > //id is vtkImageData
> >> >> > int *uExtent = id->GetUpdateExtent();
> >> >> > pPix = (unsigned char*)id->GetScalarPointer(uExtent[0], uExtent[2],
> >> >> > uExtent[4]);
> >> >> >
> >> >> > or
> >> >> >
> >> >> > pPix = (unsigned char*)id->GetScalarPointer();
> >> >> >
> >> >> > the only method I could find out. It didn't work for me. try it to
> >> >> > see
> >> >> > if it works for you.
> >> >> >
> >> >> > Yenan
> >> >> >
> >> >> > Quoting Mark Wyszomierski :
> >> >> >
> >> >> >> Yeah once you get a pointer to the pixel data in vtkImageData you
> >> >> >> can
> >> >> >> manipulate it however you want. It's just an array of values.
> >> >> >>
> >> >> >> Mark
> >> >> >>
> >> >> >> On 5/16/08, yenanqu at scs.fsu.edu wrote:
> >> >> >>> Did you retrieve pixel data from vtkImageData seccessfully?
> >> >> >>>
> >> >> >>>
> >> >> >>> Yenan
> >> >> >>> Quoting Romuald BERTRAND :
> >> >> >>>
> >> >> >>>> Hi all,
> >> >> >>>>
> >> >> >>>> I have to display an image for my work. After, I have to change
> >> >> >>>> the
> >> >> >>>> color of several pixels, I don't know why. I have a vtkImageData,
> >> >> >>>> and I have search some methods to set the scalars of the pixels
> >> >> >>>> which are stored in, but I don't arrived.
> >> >> >>>>
> >> >> >>>> Someone could help me?
> >> >> >>>>
> >> >> >>>> Thanks for answers.
> >> >> >>>>
> >> >> >>>> Romuald
> >> >> >>>>
> >> >> >>>> --
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