Halide Tutorial 02

概要

libpngを用いて入力した画像に対して処理を実行するチュートリアル。 入力した画像の輝度を1.5倍する。 Algorithm部分を分割（ワンラインではなく）してかけることを紹介している。

// Halide tutorial lesson 2: Processing images
// The only Halide header file you need is Halide.h. It includes all of Halide.
#include "Halide.h"

// Include some support code for loading pngs.
#include "halide_image_io.h"
using namespace Halide::Tools;

int main(int argc, char **argv) {

    // First we'll load the input image we wish to brighten.
    Halide::Buffer<uint8_t> input = load_image("images/rgb.png");

    // Next we define our Func object that represents our one pipeline
    // stage.
    Halide::Func brighter;

    // Our Func will have three arguments, representing the position
    // in the image and the color channel. Halide treats color
    // channels as an extra dimension of the image.
    Halide::Var x, y, c;

    // Normally we'd probably write the whole function definition on
    // one line. Here we'll break it apart so we can explain what
    // we're doing at every step.
    // 1行で書くならこうだが、分割OK
    // brighter(x, y, c) = Halide::cast<uint8_t>(min(input(x, y, c) * 1.5f, 255));

    // For each pixel of the input image.
    Halide::Expr value = input(x, y, c);

    // Cast it to a floating point value.
    value = Halide::cast<float>(value);

    // Multiply it by 1.5 to brighten it. Halide represents real
    // numbers as floats, not doubles, so we stick an 'f' on the end
    // of our constant.
    value = value * 1.5f;

    // Clamp it to be less than 255, so we don't get overflow when we
    // cast it back to an 8-bit unsigned int.
    value = Halide::min(value, 255.0f);

    // Cast it back to an 8-bit unsigned integer.
    value = Halide::cast<uint8_t>(value);

    // Define the function.
    brighter(x, y, c) = value;

    Halide::Buffer<uint8_t> output =
        brighter.realize(input.width(), input.height(), input.channels());

    // Save the output for inspection. It should look like a bright parrot.
    save_image(output, "brighter.png");

    // See figures/lesson_02_output.jpg for a small version of the output.

    printf("Success!\n");
    return 0;
}

実行コマンド

g++ lesson_02*.cpp -g -I ../include -I ../tools -L ../bin -lHalide `libpng-config --cflags --ldflags` -lpthread -ldl -o lesson_02 -std=c++11 -ljpeg
LD_LIBRARY_PATH=../bin ./lesson_02