Add Blurhash encoder

2020-12-05 00:16:27 -07:00 · 2020-12-05 00:16:27 -07:00 · fad102bf80
parent 4d22426da2
commit fad102bf80
5 changed files with 255 additions and 0 deletions
--- a/app/Util/Blurhash/AC.php
+++ b/app/Util/Blurhash/AC.php
@ -0,0 +1,34 @@
+<?php
+
+namespace App\Util\Blurhash;
+
+final class AC {
+
+    public static function encode(array $value, float $max_value): float {
+        $quant_r = static::quantise($value[0] / $max_value);
+        $quant_g = static::quantise($value[1] / $max_value);
+        $quant_b = static::quantise($value[2] / $max_value);
+        return $quant_r * 19 * 19 + $quant_g * 19 + $quant_b;
+    }
+
+    public static function decode(int $value, float $max_value): array {
+        $quant_r = floor($value / (19 * 19));
+        $quant_g = floor($value / 19) % 19;
+        $quant_b = $value % 19;
+
+        return [
+            static::signPow(($quant_r - 9) / 9, 2) * $max_value,
+            static::signPow(($quant_g - 9) / 9, 2) * $max_value,
+            static::signPow(($quant_b - 9) / 9, 2) * $max_value
+        ];
+    }
+
+    private static function quantise(float $value): float {
+        return floor(max(0, min(18, floor(static::signPow($value, 0.5) * 9 + 9.5))));
+    }
+
+    private static function signPow(float $base, float $exp): float {
+        $sign = $base <=> 0;
+        return $sign * pow(abs($base), $exp);
+    }
+}
--- a/app/Util/Blurhash/Base83.php
+++ b/app/Util/Blurhash/Base83.php
@ -0,0 +1,39 @@
+<?php
+
+namespace App\Util\Blurhash;
+
+use InvalidArgumentException;
+
+class Base83 {
+    private const ALPHABET = [
+        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D',
+        'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R',
+        'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
+        'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
+        'u', 'v', 'w', 'x', 'y', 'z', '#', '$', '%', '*', '+', ',', '-', '.',
+        ':', ';', '=', '?', '@', '[', ']', '^', '_', '{', '|', '}', '~'
+    ];
+
+    private const BASE = 83;
+
+    public static function encode(int $value, int $length): string {
+        if (floor($value / (self::BASE ** $length)) != 0) {
+            throw new InvalidArgumentException('Specified length is too short to encode given value.');
+        }
+
+        $result = '';
+        for ($i = 1; $i <= $length; $i++) {
+            $digit   = floor($value / (self::BASE ** ($length - $i))) % self::BASE;
+            $result .= self::ALPHABET[$digit];
+        }
+        return $result;
+    }
+
+    public static function decode(string $hash): int {
+        $result = 0;
+        foreach (str_split($hash) as $char) {
+            $result = $result * self::BASE + (int) array_search($char, self::ALPHABET, true);
+        }
+        return (int) $result;
+    }
+}
--- a/app/Util/Blurhash/Blurhash.php
+++ b/app/Util/Blurhash/Blurhash.php
@ -0,0 +1,139 @@
+<?php
+
+namespace App\Util\Blurhash;
+
+use InvalidArgumentException;
+
+class Blurhash {
+
+    public static function encode(array $image, int $components_x = 4, int $components_y = 4, bool $linear = false): string {
+        if (($components_x < 1 || $components_x > 9) || ($components_y < 1 || $components_y > 9)) {
+            throw new InvalidArgumentException("x and y component counts must be between 1 and 9 inclusive.");
+        }
+        $height = count($image);
+        $width  = count($image[0]);
+
+        $image_linear = $image;
+        if (!$linear) {
+            $image_linear = [];
+            for ($y = 0; $y < $height; $y++) {
+                $line = [];
+                for ($x = 0; $x < $width; $x++) {
+                    $pixel  = $image[$y][$x];
+                    $line[] = [
+                        Color::toLinear($pixel[0]),
+                        Color::toLinear($pixel[1]),
+                        Color::toLinear($pixel[2])
+                    ];
+                }
+                $image_linear[] = $line;
+            }
+        }
+
+        $components = [];
+        $scale = 1 / ($width * $height);
+        for ($y = 0; $y < $components_y; $y++) {
+            for ($x = 0; $x < $components_x; $x++) {
+                $normalisation = $x == 0 && $y == 0 ? 1 : 2;
+                $r = $g = $b = 0;
+                for ($i = 0; $i < $width; $i++) {
+                    for ($j = 0; $j < $height; $j++) {
+                        $color = $image_linear[$j][$i];
+                        $basis = $normalisation
+                                * cos(M_PI * $i * $x / $width)
+                                * cos(M_PI * $j * $y / $height);
+
+                        $r += $basis * $color[0];
+                        $g += $basis * $color[1];
+                        $b += $basis * $color[2];
+                    }
+                }
+
+                $components[] = [
+                    $r * $scale,
+                    $g * $scale,
+                    $b * $scale
+                ];
+            }
+        }
+
+        $dc_value = DC::encode(array_shift($components) ?: []);
+
+        $max_ac_component = 0;
+        foreach ($components as $component) {
+            $component[] = $max_ac_component;
+            $max_ac_component = max ($component);
+        }
+
+        $quant_max_ac_component = (int) max(0, min(82, floor($max_ac_component * 166 - 0.5)));
+        $ac_component_norm_factor = ($quant_max_ac_component + 1) / 166;
+
+        $ac_values = [];
+        foreach ($components as $component) {
+            $ac_values[] = AC::encode($component, $ac_component_norm_factor);
+        }
+
+        $blurhash  = Base83::encode($components_x - 1 + ($components_y - 1) * 9, 1);
+        $blurhash .= Base83::encode($quant_max_ac_component, 1);
+        $blurhash .= Base83::encode($dc_value, 4);
+        foreach ($ac_values as $ac_value) {
+            $blurhash .= Base83::encode((int) $ac_value, 2);
+        }
+
+        return $blurhash;
+    }
+
+    public static function decode (string $blurhash, int $width, int $height, float $punch = 1.0, bool $linear = false): array {
+        if (empty($blurhash) || strlen($blurhash) < 6) {
+            throw new InvalidArgumentException("Blurhash string must be at least 6 characters");
+        }
+
+        $size_info = Base83::decode($blurhash[0]);
+        $size_y = floor($size_info / 9) + 1;
+        $size_x = ($size_info % 9) + 1;
+
+        $length = (int) strlen($blurhash);
+        $expected_length = (int) (4 + (2 * $size_y * $size_x));
+        if ($length !== $expected_length) {
+            throw new InvalidArgumentException("Blurhash length mismatch: length is {$length} but it should be {$expected_length}");
+        }
+
+        $colors = [DC::decode(Base83::decode(substr($blurhash, 2, 4)))];
+
+        $quant_max_ac_component = Base83::decode($blurhash[1]);
+        $max_value = ($quant_max_ac_component + 1) / 166;
+        for ($i = 1; $i < $size_x * $size_y; $i++) {
+            $value = Base83::decode(substr($blurhash, 4 + $i * 2, 2));
+            $colors[$i] = AC::decode($value, $max_value * $punch);
+        }
+
+        $pixels = [];
+        for ($y = 0; $y < $height; $y++) {
+            $row = [];
+            for ($x = 0; $x < $width; $x++) {
+                $r = $g = $b = 0;
+                for ($j = 0; $j < $size_y; $j++) {
+                    for ($i = 0; $i < $size_x; $i++) {
+                        $color = $colors[$i + $j * $size_x];
+                        $basis =
+                            cos((M_PI * $x * $i) / $width) *
+                            cos((M_PI * $y * $j) / $height);
+
+                        $r += $color[0] * $basis;
+                        $g += $color[1] * $basis;
+                        $b += $color[2] * $basis;
+                    }
+                }
+
+                $row[] = $linear ? [$r, $g, $b] : [
+                    Color::toSRGB($r),
+                    Color::toSRGB($g),
+                    Color::toSRGB($b)
+                ];
+            }
+            $pixels[] = $row;
+        }
+
+        return $pixels;
+    }
+}
--- a/app/Util/Blurhash/Color.php
+++ b/app/Util/Blurhash/Color.php
@ -0,0 +1,19 @@
+<?php
+
+namespace App\Util\Blurhash;
+
+final class Color {
+    public static function toLinear(int $value): float {
+        $value = $value / 255;
+        return ($value <= 0.04045)
+            ? $value / 12.92
+            : pow(($value + 0.055) / 1.055, 2.4);
+    }
+
+    public static function tosRGB(float $value): int {
+        $normalized = max(0, min(1, $value));
+        return ($normalized <= 0.0031308)
+            ? (int) round($normalized * 12.92 * 255 + 0.5)
+            : (int) round((1.055 * pow($normalized, 1 / 2.4) - 0.055) * 255 + 0.5);
+    }
+}
--- a/app/Util/Blurhash/DC.php
+++ b/app/Util/Blurhash/DC.php
@ -0,0 +1,24 @@
+<?php
+
+namespace App\Util\Blurhash;
+
+final class DC {
+
+    public static function encode(array $value): int {
+        $rounded_r = Color::tosRGB($value[0]);
+        $rounded_g = Color::tosRGB($value[1]);
+        $rounded_b = Color::tosRGB($value[2]);
+        return ($rounded_r << 16) + ($rounded_g << 8) + $rounded_b;
+    }
+
+    public static function decode(int $value): array {
+        $r = $value >> 16;
+        $g = ($value >> 8) & 255;
+        $b = $value & 255;
+        return [
+            Color::toLinear($r),
+            Color::toLinear($g),
+            Color::toLinear($b)
+        ];
+    }
+}