PNG box blur algorithm (requires libpng & png++)

pngblur.cpp

#include <iostream>
#include <string>
#include <vector>
#include <utility>
#include <png++/png.hpp>

typedef std::vector<std::pair<size_t, size_t> > points_t;
bool verbose = false;

points_t get_points(size_t x, size_t y, png::uint_32 w, png::uint_32 h, int s) {
	points_t retval;
	if (verbose) std::cout << "For x=" << x << " & y=" << y << " (w=" << w << " & h=" << h << "):\n";
	for (int xx = -((s-1)/2); xx <= ((s-1)/2); xx++) {
		if ((int)x + xx < 0 || (int)x + xx >= w) continue;
		for (int yy = -((s-1)/2); yy <= ((s-1)/2); yy++) {
			if ((int)y + yy < 0 || (int)y + yy >= h) continue;
			if (verbose) std::cout << x + xx << ", " << y + yy << std::endl;
			retval.push_back(std::make_pair(x + xx, y + yy));
		}
	}
	if (verbose) std::cout << std::endl;
	return retval;
}

png::uint_32 avg32(std::vector<png::uint_32> a) {
	png::uint_32 retval = 0;
	for (png::uint_32 n : a) retval += n;
	return retval/a.size();
}

std::vector<png::uint_32> split_pixels(std::vector<png::rgb_pixel> p, int c) {
	std::vector<png::uint_32> retval;
	if (c == 0) for (png::rgb_pixel l : p) retval.push_back(l.red);
	else if (c == 1) for (png::rgb_pixel l : p) retval.push_back(l.green);
	else for (png::rgb_pixel l : p) retval.push_back(l.blue);
	return retval;
}

int main(int argc, const char * argv[]) {
	if (argc < 4 || std::string(argv[1]) == "-h") {
		std::cout << "Usage: " << argv[0] << " [-s size] [-l loops] [-n] [-v] -o <output> <image>\n";
		return 1;
	}
	bool halt = false;
	int loops = 1;
	int size = 3;
	const char * input = argv[argc-1];
	const char * output;
	for (int i = 1; i < argc - 1; i++) {
		if (std::string(argv[i]) == "-s") {
			size = stoi(std::string(argv[i+1]));
		} else if (std::string(argv[i]) == "-l") {
			loops = stoi(std::string(argv[i+1]));
		} else if (std::string(argv[i]) == "-o") {
			output = argv[i+1];
		} else if (std::string(argv[i]) == "-n") {
			halt = true;
		} else if (std::string(argv[i]) == "-v") {
			verbose = true;
		}
	}
	if (size % 2 != 1 || size < 3) {
		std::cout << "Error: The size given was not valid.";
		if (halt) {
			std::cout << std::endl;
			return 2;
		}
		std::cout << " Continuing with size 3...\n";
		size = 3;
	}
	png::image<png::rgb_pixel> in(input);
	png::uint_32 width = in.get_width();
	png::uint_32 height = in.get_height();
	png::image<png::rgb_pixel> out(width, height);
	for (int loop = 0; loop < loops; loop++) {
		out = png::image<png::rgb_pixel>(width, height);
		for (size_t x = 0; x < width; x++) {
			for (size_t y = 0; y < height; y++) {
				points_t l = get_points(x, y, width, height, size);
				png::rgb_pixel o;
				std::vector<png::rgb_pixel> c;
				for (std::pair<size_t, size_t> n : l) c.push_back(in.get_pixel(n.first, n.second));
				for (int i = 0; i < 3; i++) {
					png::uint_32 a = avg32(split_pixels(c, i));
					if (i == 0) o.red = a;
					else if (i == 1) o.green = a;
					else o.blue = a;
				}
				out.set_pixel(x, y, o);
			}
		}
		in = out;
		if (verbose) std::cout << "Finished loop " << loop + 1 << std::endl;
	}
	out.write(output);
	return 0;
}

This is available on my macOS Homebrew repo as mcjack123/pngblur.