Introduction to Halide

Introduction

Halide is a programming language for writing high-performance image and array processing code. It is designed to be used on modern machines, including CPUs, GPUs, and mobile devices. Halide code is written in a high-level language that is similar to C++, but it is compiled to machine code for the specific target platform. This allows Halide to achieve high performance while still being easy to use.

Halide provides a number of features that make it well-suited for image and array processing, including:

Heterogeneous compilation: Halide can be compiled to run on CPUs, GPUs, and mobile devices. This allows you to choose the best platform for your specific application.
Automatic parallelization: Halide automatically parallelizes your code across multiple cores. This can significantly improve the performance of your code.
Flexible scheduling: Halide allows you to control the order in which your code is executed. This can be useful for optimizing the performance of your code for specific applications.
Image processing primitives: Halide provides a number of image processing primitives, such as convolution, edge detection, and image resizing. This can save you time and effort when writing image processing code.

To use Halide, you first need to install the Halide runtime. Once the runtime is installed, you can write Halide code and compile it to machine code using the g++ compiler or the clang++ compiler.

Example

Here is a simple example of a Halide program that blurs an image:

#include <Halide.h>

int main(int argc, char** argv) {
  // Create an input image.
  var input = image.input("input", image.rgb);

  // Compute the blur of the image.
  var output = input.blur(3);

  // Save the output image.
  output.store("output.png");

  return 0;
}

This program takes an input image and computes the blur of the image. The blur is computed using a 3x3 convolution kernel. The output image is saved to a file called output.png.

To compile this program, you can use the following command:

g++ -std=c++11 -O3 -Wall -ffast-math -I/path/to/halide/include blur.cpp -o blur

This command will compile the program to machine code using the g++ compiler. You can then run the program by typing the following command:

./blur

The blurred image will be saved to a file called output.png.

Python version

In addition to the C++ version, Halide also has a Python version. The Python version is similar to the C++ version, but it uses the Python programming language instead of C++.

Here is a simple example of a Halide program in Python that blurs an image:

import halide as hl

def main():
  # Create an input image.
  input = hl.image.input("input", hl.type.rgb)

  # Compute the blur of the image.
  output = input.blur(3)

  # Save the output image.
  output.store("output.png")

if __name__ == "__main__":
  main()

This program is functionally equivalent to the C++ program above. The only difference is that it is written in Python instead of C++.

To run this program, you can use the following command:

python blur.py

The blurred image will be saved to a file called output.png.