image thresholding

Image/Thresholding.php

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+<?php
+/**
+ * Orange Management
+ *
+ * PHP Version 8.0
+ *
+ * @package   phpOMS\Image
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 1.0
+ * @version   1.0.0
+ * @link      https://orange-management.org
+ */
+declare(strict_types=1);
+
+namespace phpOMS\Image;
+
+/**
+ * Image thresholding
+ *
+ * @package phpOMS\Image
+ * @license OMS License 1.0
+ * @link    https://orange-management.org
+ * @since   1.0.0
+ */
+final class Thresholding
+{
+    /**
+     * Perform integral thresholding
+     *
+     * @param string $inPath  Image path to process
+     * @param string $outPath Output path to store the processed image
+     *
+     * @return void
+     *
+     * @see https://people.scs.carleton.ca/~roth/iit-publications-iti/docs/gerh-50002.pdf
+     * @see http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.817.6856&rep=rep1&type=pdf
+     *
+     * @since 1.0.0
+     */
+    public static function integralThresholding(string $inPath, string $outPath) : void
+    {
+        $im = null;
+        if (\strripos($inPath, 'png') !== false) {
+            $im = \imagecreatefrompng($inPath);
+        } elseif (\strripos($inPath, 'jpg') !== false || \strripos($inPath, 'jpeg') !== false) {
+            $im = \imagecreatefromjpeg($inPath);
+        } else {
+            $im = \imagecreatefromgif($inPath);
+        }
+
+        $dim = \getimagesize($inPath);
+        $out = \imagecreate($dim[0], $dim[1]);
+
+        $intImg = [[]];
+
+        $s = (int) $dim[0] / 24; // can be changed 8
+        $t = 30; // can be changed 15
+
+        for ($i = 0; $i < $dim[0]; ++$i) {
+            $sum = 0;
+
+            for ($j = 0; $j < $dim[1]; ++$j) {
+                $rgb = \imagecolorat($im, $i, $j);
+                $sum += self::lightness($rgb);
+
+                $intImg[$i][$j] = $i === 0 ? $sum : $intImg[$i - 1][$j] + $sum;
+            }
+        }
+
+        $black = \imagecolorallocate($out, 0, 0, 0);
+        $white = \imagecolorallocate($out, 255, 255, 255);
+
+        for ($i = 0; $i < $dim[0]; ++$i) {
+            for ($j = 0; $j < $dim[1]; ++$j) {
+                $x1 = \max(1, (int) ($i - $s / 2));
+                $x2 = \min((int) ($i + $s / 2), $dim[0] - 1);
+
+                $y1 = \max(1, (int) ($j - $s / 2));
+                $y2 = \min((int) ($j + $s / 2), $dim[1] - 1);
+
+                $count = ($x2 - $x1) * ($y2 - $y1);
+                $sum   = $intImg[$x2][$y2] - $intImg[$x2][$y1 - 1] - $intImg[$x1 - 1][$y2] + $intImg[$x1 - 1][$y1 - 1];
+
+                $rgb = \imagecolorat($im, $i, $j);
+                $brightness = self::lightness($rgb);
+
+                $color = $brightness * $count <= ($sum * (100 - $t) / 100) ? $black : $white;
+
+                \imagesetpixel($out, $i, $j, $color);
+            }
+        }
+
+        if (\strripos($outPath, 'png') !== false) {
+            \imagepng($out, $outPath);
+        } elseif (\strripos($outPath, 'jpg') !== false || \strripos($outPath, 'jpeg') !== false) {
+            \imagejpeg($out, $outPath);
+        } else {
+            \imagegif($out, $outPath);
+        }
+
+        \imagedestroy($out);
+    }
+
+    private static function lightness(int $rgb) : float
+    {
+        $sR = ($rgb >> 16) & 0xFF;
+        $sG = ($rgb >> 8) & 0xFF;
+        $sB = $rgb & 0xFF;
+
+        $vR = $sR / 255;
+        $vG = $sG / 255;
+        $vB = $sB / 255;
+
+        $lR = $vR <= 0.04045 ? $vR / 12.92 : \pow((($vR + 0.055) / 1.055), 2.4);
+        $lG = $vG <= 0.04045 ? $vG / 12.92 : \pow((($vG + 0.055) / 1.055), 2.4);
+        $lB = $vB <= 0.04045 ? $vB / 12.92 : \pow((($vB + 0.055) / 1.055), 2.4);
+
+        $y = 0.2126 * $lR + 0.7152 * $lG + 0.0722 * $lB;
+        $lStar = $y <= 216 / 24389 ? $y * 24389 / 27 : \pow($y,(1 / 3)) * 116 - 16;
+
+        return $lStar / 100;
+    }
+}

tests/Image/ThresholdingTest.php

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+<?php
+/**
+ * Orange Management
+ *
+ * PHP Version 8.0
+ *
+ * @package   tests
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 1.0
+ * @version   1.0.0
+ * @link      https://orange-management.org
+ */
+declare(strict_types=1);
+
+namespace phpOMS\tests\Image;
+
+require_once __DIR__ . '/../Autoloader.php';
+
+use phpOMS\Image\Thresholding;
+
+/**
+ * @internal
+ */
+final class ThresholdingTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @group framework
+     * @coversNothing
+     */
+    public function testThresholding() : void
+    {
+        Thresholding::integralThresholding(__DIR__ . '/img1.png', __DIR__ . '/test_img1.png');
+        Thresholding::integralThresholding(__DIR__ . '/img2.jpg', __DIR__ . '/test_img2.jpg');
+    }
+}