Add encoding

LICENSE

@@ -0,0 +1,23 @@
+Boost Software License - Version 1.0 - August 17th, 2003
+
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.

blurhash.cpp

@@ -1,3 +1,5 @@
+#include "blurhash.hpp"
+
 #include <algorithm>
 #include <array>
 #include <cassert>
@@ -5,13 +7,12 @@
 #include <vector>
 
 #ifdef DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
-#define STB_IMAGE_WRITE_IMPLEMENTATION
-#include "stb_image_write.h"
 #include <doctest.h>
 #endif
 
 using namespace std::literals;
 
+namespace {
 constexpr std::array<char, 84> int_to_b83{
   "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~"};
 
@@ -98,7 +99,7 @@ decodeMaxAC(std::string_view maxAC)
 int
 encodeMaxAC(float maxAC)
 {
-        return int(std::max(0., std::min(82., std::floor(maxAC * 166 - 0.5))));
+        return std::max(0, std::min(82, int(maxAC * 166 - 0.5)));
 }
 
 float
@@ -224,13 +225,29 @@ decodeAC(std::string_view value, float maximumValue)
         return decodeAC(decode83(value), maximumValue);
 }
 
-namespace blurhash {
-struct Image
+Color
+multiplyBasisFunction(Components components, int width, int height, unsigned char *pixels)
 {
-        size_t width, height;
-        std::vector<unsigned char> image; // pixels rgb
-};
+        Color c{};
+        float normalisation = (components.x == 0 && components.y == 0) ? 1 : 2;
 
+        for (int y = 0; y < height; y++) {
+                for (int x = 0; x < width; x++) {
+                        float basis = std::cos(M_PI * components.x * x / float(width)) *
+                                      std::cos(M_PI * components.y * y / float(height));
+                        c.r += basis * srgbToLinear(pixels[3 * x + 0 + y * width * 3]);
+                        c.g += basis * srgbToLinear(pixels[3 * x + 1 + y * width * 3]);
+                        c.b += basis * srgbToLinear(pixels[3 * x + 2 + y * width * 3]);
+                }
+        }
+
+        float scale = normalisation / (width * height);
+        c *= scale;
+        return c;
+}
+}
+
+namespace blurhash {
 Image
 decode(std::string_view blurhash, size_t width, size_t height)
 {
@@ -284,6 +301,58 @@ decode(std::string_view blurhash, size_t width, size_t height)
 
         return i;
 }
+
+std::string
+encode(unsigned char *image, size_t width, size_t height, int components_x, int components_y)
+{
+        if (width < 1 || height < 1 || components_x < 1 || components_x > 9 || components_y < 1 ||
+            components_y > 9 || !image)
+                return "";
+
+        std::vector<Color> factors;
+        factors.reserve(components_x * components_y);
+        for (int y = 0; y < components_y; y++) {
+                for (int x = 0; x < components_x; x++) {
+                        factors.push_back(multiplyBasisFunction({x, y}, width, height, image));
+                }
+        }
+
+        assert(factors.size() > 0);
+
+        auto dc = factors.front();
+        factors.erase(factors.begin());
+
+        std::string h;
+
+        h += leftPad(encode83(packComponents({components_x, components_y})), 1);
+
+        float maximumValue;
+        if (!factors.empty()) {
+                float actualMaximumValue = 0;
+                for (auto ac : factors) {
+                        actualMaximumValue = std::max({
+                          std::abs(ac.r),
+                          std::abs(ac.g),
+                          std::abs(ac.b),
+                          actualMaximumValue,
+                        });
+                }
+
+                int quantisedMaximumValue = encodeMaxAC(actualMaximumValue);
+                maximumValue = ((float)quantisedMaximumValue + 1) / 166;
+                h += leftPad(encode83(quantisedMaximumValue), 1);
+        } else {
+                maximumValue = 1;
+                h += leftPad(encode83(0), 1);
+        }
+
+        h += leftPad(encode83(encodeDC(dc)), 4);
+
+        for (auto ac : factors)
+                h += leftPad(encode83(encodeAC(ac, maximumValue)), 2);
+
+        return h;
+}
 }
 
 #ifdef DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
@@ -386,4 +455,16 @@ TEST_CASE("decode")
         CHECK(i1.height == 0);
         CHECK(i1.image.size() == 0);
 }
+
+TEST_CASE("encode")
+{
+        CHECK(blurhash::encode(nullptr, 360, 200, 4, 3) == "");
+
+        std::vector<unsigned char> black(360 * 200 * 3, 0);
+        CHECK(blurhash::encode(black.data(), 0, 200, 4, 3) == "");
+        CHECK(blurhash::encode(black.data(), 360, 0, 4, 3) == "");
+        CHECK(blurhash::encode(black.data(), 360, 200, 0, 3) == "");
+        CHECK(blurhash::encode(black.data(), 360, 200, 4, 0) == "");
+        CHECK(blurhash::encode(black.data(), 360, 200, 4, 3) == "L00000fQfQfQfQfQfQfQfQfQfQfQ");
+}
 #endif

blurhash.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <string_view>
+#include <vector>
+
+namespace blurhash {
+struct Image
+{
+        size_t width, height;
+        std::vector<unsigned char> image; // pixels rgb
+};
+
+// Decode a blurhash to an image with size width*height
+Image
+decode(std::string_view blurhash, size_t width, size_t height);
+
+// Encode an image of rgb pixels (without padding) with size width*height into a blurhash with x*y
+// components
+std::string
+encode(unsigned char *image, size_t width, size_t height, int x, int y);
+}

blurhash2bmp.cpp

@@ -0,0 +1,43 @@
+#include "blurhash.hpp"
+
+#include <charconv>
+#include <iostream>
+
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include "stb_image_write.h"
+
+int
+main(int argc, char **argv)
+{
+        if (argc != 5) {
+                std::cerr << "Usage: blurhash2bmp [hash] [width] [height] [output name]"
+                          << std::endl;
+                return -2;
+        }
+
+        int height = 0, width = 0;
+
+        std::string_view width_str{argv[2]}, height_str{argv[3]};
+        std::from_chars(height_str.begin(), height_str.end(), height);
+        if (height <= 0) {
+                std::cerr << "Invalid height.";
+                return -2;
+        }
+        std::from_chars(width_str.begin(), width_str.end(), width);
+        if (width <= 0) {
+                std::cerr << "Invalid width.";
+                return -2;
+        }
+
+        blurhash::Image image = blurhash::decode(argv[1], width, height);
+        if (image.image.empty()) {
+                std::cerr << "Decode failed.";
+                return -1;
+        }
+        if (!stbi_write_bmp(argv[4], image.width, image.height, 3, (void *)image.image.data())) {
+                std::cerr << "Image write failed.";
+                return -1;
+        }
+
+        return 0;
+}

image2blurhash.cpp

@@ -0,0 +1,47 @@
+#include "blurhash.hpp"
+
+#include <charconv>
+#include <iostream>
+
+#define STB_IMAGE_IMPLEMENTATION
+#include "stb_image.h"
+
+int
+main(int argc, char **argv)
+{
+        if (argc != 4) {
+                std::cerr << "Usage: blurhash [filename] [num x components] [num y components]"
+                          << std::endl;
+                return -2;
+        }
+
+        int x = 0, y = 0;
+
+        std::string_view x_str{argv[2]}, y_str{argv[3]};
+        std::from_chars(x_str.begin(), x_str.end(), x);
+        if (x <= 0 || x > 9) {
+                std::cerr << "Invalid x components, should be between 1 and 9." << std::endl;
+                return -2;
+        }
+        std::from_chars(y_str.begin(), y_str.end(), y);
+        if (y <= 0 || y > 9) {
+                std::cerr << "Invalid y components, should be between 1 and 9." << std::endl;
+                return -2;
+        }
+
+        int width, height, n;
+        unsigned char *data = stbi_load(argv[1], &width, &height, &n, 3);
+        if (!data) {
+                std::cerr << "Image loading failed for file '" << argv[1] << "'." << std::endl;
+                return -1;
+        }
+        if (n != 3) {
+                std::cerr << "Couldn't decode image to 3 channel rgb." << std::endl;
+                return -1;
+        }
+        std::cout << blurhash::encode(data, width, height, x, y) << std::endl;
+
+        stbi_image_free(data);
+
+        return 0;
+}

meson.build

@@ -2,7 +2,7 @@ project('blurhash', 'cpp',
   version : '0.1',
   default_options : ['warning_level=3', 'cpp_std=c++17'])
 
-static_library('blurhash',
+lib = static_library('blurhash',
            'blurhash.cpp',
            install : true)
 
@@ -14,3 +14,6 @@ tests = executable('blurhash-tests',
 	   dependencies: doctest_dep,
            install : false)
 test('blurhash-tests', tests)
+
+executable('blurhash2bmp', 'blurhash2bmp.cpp', link_with: lib, install: true)
+executable('blurhash', 'image2blurhash.cpp', link_with: lib, install: true)