halide_cv_utils.cpp

#include "halide_cv_utils.h"

uint16_t RGB2Y[3] = {4899,  9617, 1868};

Halide::Func gray(Halide::Buffer<uint8_t> in){
    Halide::Var x("x1"), y("y1"), c("c1");

    //TODO: make assert instead
    if(in.channels() != 3){
        Halide::Func ret;
        ret(x, y, c) = in(x, y , c);
        return ret;
    }


    Halide::Func casted("casted");
    casted(x, y, c) = Halide::cast<uint32_t>(in(x, y, c));

    Halide::Expr ycomp = RGB2Y[0] * casted(x, y, 0) +
                         RGB2Y[1] * casted(x, y, 1) +
                         RGB2Y[2] * casted(x, y, 2);
    ycomp = ycomp >> 14;   //equivalent to multiplying by [0.299, 0.587, 0.114]

    Halide::Func gr("gray");
    gr(x, y) = Halide::cast<uint8_t>(ycomp);


    //optimizing below
    Halide::Var x_outer, y_outer, x_inner, y_inner, tile_index;
    gr.tile(x, y, x_outer, y_outer, x_inner, y_inner, 64, 64)
      .fuse(x_outer, y_outer, tile_index)
      .parallel(tile_index);
    Halide::Var x_inner_outer, y_inner_outer, x_vectors, y_pairs;
    gr.tile(x_inner, y_inner, x_inner_outer, y_inner_outer, x_vectors, y_pairs, 4, 2)
      .vectorize(x_vectors)
      .unroll(y_pairs);

    return gr;
}