[vtkusers] How get pixel data in VTK?

Thu Apr 24 13:20:31 EDT 2008

You have to remember to reply to the vtk users board as well, don't direct
the emails to just me.

How big is your render window, you're only sampling the first 1041 / 3
pixels there, and I wouldn't be surprised if they were all black. You should
also verify that the image data is 3 component unsigned char. I would also
make sure that your png actually contains something by just writing it to
disk.

Mark

On Thu, Apr 24, 2008 at 1:15 PM, <yenanqu at scs.fsu.edu> wrote:

>
> Here is my code:
> ======================================
> renWin->Render();
> vtkWindowToImageFilter * w2i = vtkWindowToImageFilter::New();
> vtkPNGWriter * writer = vtkPNGWriter::New();
> w2i->SetInput( renWin );
> writer->SetInput( w2i->GetOutput() );
> w2i->Update();
> vtkImageData * id = w2i->GetOutput();
> id->Update();
> //int* siz = id->GetDimensions();
> //unsigned long ms = id->GetActualMemorySize();
> //int ms1 = id->GetScalarSize();
> unsigned char* pPix;
> pPix = (unsigned char*)id->GetScalarPointer();
>
> for(int ee=0;ee<1041;ee++){
>   int pp = pPix[ee];
>   cout<<" "<<pp;
> }
> ===============================================
> The thing I can be sure is there is no problem with id (vtkImageData)
>
>
> Yenan
>
>
>
> Quoting Mark Wyszomierski <markww at gmail.com>:
>
>  Are you sure you actually set any of the RGB components in the first
>> place?
>> You could just be allocating the image array, all elements are set to
>> zero,
>> and you'll just get a zero for every element you access.
>>
>> Mark
>>
>> On Thu, Apr 24, 2008 at 12:49 PM, <yenanqu at scs.fsu.edu> wrote:
>>
>>  when I do
>>> "unsigned char *pVtkPix = (unsigned char *)pImgData->GetScalarPointer();"
>>> it doesn't seem to get the scarlar pointer, I have already do all the
>>> update thing before this, and I also could get dimensions from pImgData.
>>> but
>>> when I output all the RGB value with your method, they are all 0.
>>> this stuff really kills me~~~
>>>
>>>
>>> Yenan
>>>
>>>
>>> Quoting Mark Wyszomierski <markww at gmail.com>:
>>>
>>>  I think the RGB pixel data is usually allocated like:
>>>
>>>>
>>>>   RGBRGBRGB etc....
>>>>
>>>> so you have numPixels * 3 actual elements in your image data array.
>>>>
>>>> You get a pixel pointer as usual and cast it to (unsigned char*):
>>>>
>>>> // Get a pointer to the actual pixel data.
>>>> unsigned char *pVtkPix = (unsigned char *)pImgData->GetScalarPointer();
>>>>
>>>> // These are the r,g and b values for the first pixel:
>>>> int rr  = pVtkPix[0];
>>>> int gg = pVtkPix[1];
>>>> int bb = pVtkPix[2];
>>>>
>>>> // For the second pixel:
>>>> rr  = pVtkPix[3];
>>>> gg = pVtkPix[4];
>>>> bb = pVtkPix[5];
>>>>
>>>> and so on. Make sure you don't have RGBA data, if you do, then you just
>>>> have
>>>> an extra index per pixel which is the alpha component. Let me know if
>>>> that
>>>> helps,
>>>>
>>>> Mark
>>>>
>>>>
>>>> On Wed, Apr 23, 2008 at 7:08 PM, <yenanqu at scs.fsu.edu> wrote:
>>>>
>>>>  Hi, Mark, I did have the data that is three component. Your example
>>>> only
>>>>
>>>>> shows how to get pixel data that is one component which I never got in
>>>>> my
>>>>> code before. Do you have any idea how to retrieve this three component
>>>>> data?
>>>>> I have try bunch of methods, but none of them is working. any help will
>>>>> be
>>>>> greatly appreciated.
>>>>>
>>>>> Yenan
>>>>>
>>>>> Quoting Mark Wyszomierski <markww at gmail.com>:
>>>>>
>>>>>  Hi,
>>>>> >
>>>>> > It's definitely possible to get the scalar value from a vtkImageData
>>>>> > object. You need to know the type of data your object is stored in
>>>>> > though, for example you'll have difficulty getting the scalar value
>>>>> if
>>>>> > your data is three component RGB and you're trying to get a single
>>>>> > pixel scalar pixel value.
>>>>> >
>>>>> > I have an example of getting the pixel value that the mouse moves
>>>>> over
>>>>> > in an image here:
>>>>> >
>>>>> >
>>>>> >
>>>>>
>>>>> http://devsample.org/index.php?option=com_content&task=view&id=48&Itemid=27
>>>>> >
>>>>> > which may help.
>>>>> >
>>>>> > Mark
>>>>> >
>>>>> >
>>>>> > On Thu, Mar 27, 2008 at 1:37 PM,  <yenanqu at scs.fsu.edu> wrote:
>>>>> >
>>>>> > > Hi, all,
>>>>> > > I found bunch of the VTK methods to retrieve pixel data from vtk
>>>>> > > object, such as
>>>>> > > GetPixelData, GetRGBACharPixelData, etc, but none of them is
>>>>> working,
>>>>> > > Does anyone know how to get pixel data from VTK object? Thanks in
>>>>> > > advance.
>>>>> > >
>>>>> > > Yenan
>>>>> > >
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