The ResizeKernel scales an image horizontally or vertically according to the value of the Horizontal parameter. The Scale can also be controlled by the user.

Chain two BlinkScript nodes containing this kernel together, one with Horizontal checked and one without, for a two-dimensional resize.

//ResizeKernel: scale the input horizontally or vertically using a bilinear filter. 
kernel ResizeKernel : ImageComputationKernel<eComponentWise>
  Image<eRead, eAccessRandom, eEdgeConstant> src; //Output will be black outside the original image
  Image<eWrite, eAccessPoint> dst;

  float _externalScale;
  bool _horizontal; 

  float _scale;

  void define()
    defineParam(_externalScale, "Scale", 0.5f);
    defineParam(_horizontal, "Horizontal", true);

  void init()
    _scale = 1.0f/_externalScale;  //invert the scale as we back-map from dst to src

  void process(int2 pos)
    //Work out the scaled src position.
    const float xPos = (_horizontal ? (float)pos.x * _scale : (float)pos.x);
    const float yPos = (_horizontal ? pos.y : (float)pos.y * _scale);

    //Use a bilinear filter to get the value at that src position.
    dst() = bilinear(src, xPos, yPos);