local_histogram.cpp

// g++ local_histogram*.cpp -g -I ../include -L ../bin -lHalide -o local_histogram
// DYLD_LIBRARY_PATH=../bin ./local_histogram

#include <Halide.h>
#include <stdio.h>
using namespace Halide;
#include "image_io.h"

int main(int argc, char **argv) {
    Var x,y,v;
    
    Image<uint8_t> img = load<uint8_t>("images/gray.png");
    
    // Create a level image
    Func level_image("level_image");
    level_image(x,y,v) = cast<uint8_t>(0);
    level_image(x,y,img(x,y)) = cast<uint8_t>(1);
    level_image.compute_root().parallel(y);

    // Clamp level image
    Func clamped_lir("clamped_lir");
    Expr clamped_x = clamp(x, 0, img.width()-1);
    Expr clamped_y = clamp(y, 0, img.height()-1);
    clamped_lir(x,y,v) = clamp(level_image(clamped_x, clamped_y, v), 0, 63);

    // Naive histogram (vertical only)
    Func hist1("hist1");
    RDom r(-2,5);
    hist1(x,y,v) = sum(clamped_lir(x,y+r,v));
    
    // fprintf(stderr, "Start...");
    // auto out = hist1.realize(img.width(), img.height(), 64);
    // fprintf(stderr, "done.\n");
    
    // "Smart" histogram (vertical only)
    Func hist2("hist2");
    hist2(x,y,v) = cast<uint8_t>(0);
    // RDom r(-2,5);
    hist2(x,0,v) = sum(clamped_lir(x,r,v));
    RDom ry(1, img.height()-1);
    hist2(x,ry,v) = hist2(x,ry-1,v) - clamped_lir(x,ry-3,v) + clamped_lir(x,ry+2,v);

    fprintf(stderr, "Start...");
    auto out = hist2.realize(img.width(), img.height(), 64);
    fprintf(stderr, "done.\n");
}