Overview

Gaussian pyramid generator takes one input image and fills the output image pyramid with downscaled versions of the input.

Input	Gaussian kernel	Output
	7x7 support, \[ \sigma=1.7 \]

Implementation

The function is implemented by generating the Gaussian pyramid from the base (level 0) to coarser levels.

For the first level, if the underlying image is different from input, it is an exact copy of the latter.

The coarser levels are generated by taking the previous level, convolving it using a clamp boundary condition with the following kernel:

\[ k = \begin{bmatrix} 1 \\ 4 \\ 6 \\ 4 \\ 1 \end{bmatrix} \cdot \begin{bmatrix} 1 & 4 & 6 & 4 & 1 \end{bmatrix} \]

Because only 2x downscaling is supported, the result is then downsampled by keeping all pixels with even coordinates.

The algorithms repeats until all levels are generated.

Initialization phase
1. Include the header that defines the Gaussian pyramid generator function
  #include <vpi/algo/GaussianPyramidGenerator.h>
2. Define the stream on which the algorithm will be executed and the input image.
  VPIStream stream = /*...*/;
  
  VPIImage input = /*...*/;
3. Create the output pyramid with the desired number of levels and scale factor
  uint32_t w,h;
  
  vpiImageGetSize(input, &w, &h);
  
  VPIImageType type;
  
  vpiImageGetType(input, &type);
  
  VPIPyramid output;
  
  vpiPyramidCreate(w, h, type, 4, 0.5, 0, &output);
Processing phase
1. Submit the algorithm to the stream, along with the input image and output pyramid.
  vpiSubmitGaussianPyramidGenerator(stream, input, output);
2. Optionally wait until the processing is done
  vpiStreamSync(stream);

Constraints for specific backends superceed the ones specified for all backends.