[vtkusers] possible bugs in vtkImageMapper - help!

[Glen.Coates at csiro.au]

Hi,

I've got two problems with the vtkImageMapper class from the 4.1.1 
sources.  

The first is easily fixed.  The default values for ColorWindow and 
ColorLevel are 2000 and 1000 respectively, which (correctly) gives a color 
shift of 0, however results in a color scale of around 0.125, meaning the 
mapped image is 8 times as dark as the original image.  These defaults 
should be changed to 255 and 127.5 respectively in order to return the 
original image.  I don't know why the defaults have been set as they 
currently are, as no explanation is given in the sources.

The second I am stumped by.  With vtkImageMapper::RenderToRectangle 
enabled, images are scaled _larger_ when the window drops _below_ a 
certain size.  For one thing, I can't understand what window size has to 
do with the scaling of an image if we're dealing in non-normalized 
viewport coordinates.  I've done some fiddling, and this applies along 
both x & y axes, but let's say we're worried about the x axis:

Let o = x component of image origin (as set by SetPosition())
    d = x component of image dimensions (as set by SetPosition2())
    w = window width

As soon as w < o+d, the image begins scaling in the opposite direction to 
what you'd expect (ie it gets larger when the window is shrinking).  I've 
attached code that should demonstrate this behaviour (which has only been 
tested on Linux, which means that the vtkOpenGLImageMapper could be at 
fault).  If you resize the window smaller in either direction, you will 
see the image stretch out in the _wrong_ direction.

Run the program as ./stretch [jpegfile].  I have attached a small JPEG for 
testing.

If anyone's seen this behaviour before and knows of a workaround, please 
let me know as this is a major impediment to a project at the moment.

-- 
Cheers,
Glen
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#include <vtkActor.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkJPEGReader.h>
#include <vtkImageMapper.h>
#include <vtkActor2D.h>

#include <iostream>
#include <math.h>
using namespace std;

#define WINWIDTH 300
#define WINHEIGHT 300

int main(int argc, char **argv)
{
    int dims[3];
    
    vtkJPEGReader *jpeg = vtkJPEGReader::New();{
        jpeg->SetFileName(argv[1]);
        jpeg->Update();
        jpeg->GetOutput()->GetDimensions(dims);
    }

    vtkImageMapper *mapper = vtkImageMapper::New();{
        mapper->SetInput(jpeg->GetOutput());
        mapper->RenderToRectangleOn();
    }

    vtkActor2D *actor = vtkActor2D::New();{
        actor->SetMapper(mapper);
        actor->GetPosition2Coordinate()->SetCoordinateSystemToViewport();
        actor->SetPosition(0,0);
        actor->SetPosition2(dims[0],dims[1]);
    }
    
    vtkRenderer *ren = vtkRenderer::New();{
        ren->AddActor(actor);
    }

    vtkRenderWindow *win = vtkRenderWindow::New();{
        win->AddRenderer(ren);
        win->SetSize(dims[0],dims[1]);
    }
        
    vtkRenderWindowInteractor *rwi = vtkRenderWindowInteractor::New();{
        rwi->SetRenderWindow(win);
        rwi->Start();
    }

    return 0;
}
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