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// Halide tutorial lesson 2: Processing images// Halide入门教程第二讲：处理图像// This lesson demonstrates how to pass in input images and manipulate them.// 本课说明了如何读入及处理图像// On linux, you can compile and run it like so:// 在linux下，你可以按照如下方式编译和运行代码// 运行之前确保操作系统安装了libpng和libjpeg库，可以到对应的sourceforge上找到对应的代码// 编译安装,或者采用linux系统的包管理系统进行安装:// sudo apt-get install libpng// sudo apt-get install libjpeg// g++ lesson_02*.cpp -g -I ../include -I ../tools -L ../bin -lHalide `libpng-config --cflags --ldflags` -ljpeg -lpthread -ldl -o lesson_02 -std=c++11// LD_LIBRARY_PATH=../bin ./lesson_02// On os x:// g++ lesson_02*.cpp -g -I ../include -I ../tools -L ../bin -lHalide `libpng-config --cflags --ldflags` -ljpeg -o lesson_02 -std=c++11// DYLD_LIBRARY_PATH=../bin ./lesson_03// If you have the entire Halide source tree, you can also build it by// running://    make tutorial_lesson_02_input_image// in a shell with the current directory at the top of the halide// source tree.// 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.// halide_image_io.h提供了png格式图片的读写代码#include "halide_image_io.h"using namespace Halide::Tools;int main(int argc, char **argv) {    // This program defines a single-stage imaging pipeline that    // brightens an image.    // 该程序定义了一级流水级的图像处理流水线来提升图像亮度    // First we'll load the input image we wish to brighten.    // halide_image_io.h提供的图像IO函数，读入要处理的图像数据，    // 所读入的图像为8位无符号数。    Halide::Buffer
   
     input = load_image("images/rgb.png");    // See figures/lesson_02_input.jpg for a smaller version.    // Next we define our Func object that represents our one pipeline    // stage.    // 接下来定义Func函数对象来表示我们的一级图像处理流水级。    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.    // Func将有三个参数，即图像像素的索引变量，分别为：    // x，y为坐标索引，c为RGB颜色通道索引。    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.    // For each pixel of the input image.    // value表达式表示c通道（x，y）坐标处的像素值    Halide::Expr value = input(x, y, c);    // Cast it to a floating point value.    // 为了进行浮点计算，先将数据类型转换成单精度浮点类型    value = Halide::cast
    
     (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.    // 将c通道（x，y）坐标处的像素值乘1.5来提升亮度    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.    // 为了防止数据溢出，将放大后的像素值限制在[0,255]区间（又称饱和处理），并转换成8位无符号整型    value = Halide::min(value, 255.0f);    // Cast it back to an 8-bit unsigned integer.    value = Halide::cast
     
      (value);    // Define the function.    // 定义函数，即将亮度提升后的像素值，赋值给函数对象的（x，y，c）点    brighter(x, y, c) = value;    // The equivalent one-liner to all of the above is:    // 以上函数的定义可用一行来表示：    // brighter(x, y, c) = Halide::cast
      
       (min(input(x, y, c) * 1.5f, 255));    //    // In the shorter version:    // - I skipped the cast to float, because multiplying by 1.5f does    //   that automatically.    // - I also used an integer constant as the second argument in the    //   call to min, because it gets cast to float to be compatible    //   with the first argument.    // - I left the Halide:: off the call to min. It's unnecessary due    //   to Koenig lookup.    // Remember, all we've done so far is build a representation of a    // Halide program in memory. We haven't actually processed any    // pixels yet. We haven't even compiled that Halide program yet.    // 上述所有操作只是在内存中建立Halide程序，告诉Halide怎么去进行算法操作，即对算法进行了定义。    // 实际上还没有开始进行任何像素的处理。甚至Halide程序还没有进行编译    // So now we'll realize the Func. The size of the output image    // should match the size of the input image. If we just wanted to    // brighten a portion of the input image we could request a    // smaller size. If we request a larger size Halide will throw an    // error at runtime telling us we're trying to read out of bounds    // on the input image.    // 现在将实现函数。输出图像的尺寸必须和输入图像的尺寸相匹配。如果我们只想提高输入图像部分区域    //像素点的亮度，可以指定一个小一点的尺寸。如果需要一个更大尺寸的输出，Halide在运行时会抛出一个    //错误告诉我们，边界超出输入图像。    Halide::Buffer
       
         output =        brighter.realize(input.width(), input.height(), input.channels());    // Save the output for inspection. It should look like a bright parrot.    // 写下被处理过的图像    save_image(output, "brighter.png");    // See figures/lesson_02_output.jpg for a small version of the output.    printf("Success!\n");    return 0;}
       
      
     
    
   

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