     {
         Pixel d;
         initPixel(&d);
-        Scalar sf = 0.f;
+        float sf = -1.f;
 
         // composite slices for this image line
         for (int slice=firstSlice; slice!=lastSlice; slice += sliceStep)

#endif
   if(Base::preIntegration)
   {
       shmsize += Base::intImg->width*sizeof(Scalar);
   }
#ifdef NOSHMEM
   if(Base::sliceInterpol)

            if(preInt)
            {
                const float sb = volume(vidx, line-iPosY, slice, principal);
                if(sf[ix] >= 0.f)
                {
                    const float4 c = tex2D(tex_preint, sf[ix], sb);

