:octocat: optional color negation in the reader

src/Decoder/GDLuminanceSource.php

@@ -16,7 +16,7 @@ namespace chillerlan\QRCode\Decoder;
 use chillerlan\Settings\SettingsContainerInterface;
 use function file_get_contents, get_resource_type, imagecolorat, imagecolorsforindex,
 	imagecreatefromstring, imagefilter, imagesx, imagesy, is_resource;
-use const IMG_FILTER_BRIGHTNESS, IMG_FILTER_CONTRAST, IMG_FILTER_GRAYSCALE, PHP_MAJOR_VERSION;
+use const IMG_FILTER_BRIGHTNESS, IMG_FILTER_CONTRAST, IMG_FILTER_GRAYSCALE, IMG_FILTER_NEGATE, PHP_MAJOR_VERSION;
 
 /**
  * This class is used to help decode images from files which arrive as GD Resource
@@ -41,7 +41,7 @@ class GDLuminanceSource extends LuminanceSourceAbstract{
 
 		/** @noinspection PhpFullyQualifiedNameUsageInspection */
 		if(
-			(PHP_MAJOR_VERSION >= 8 && !$gdImage instanceof \GdImage)
+			(PHP_MAJOR_VERSION >= 8 && !$gdImage instanceof \GdImage) // @todo: remove version check in v6
 			|| (PHP_MAJOR_VERSION < 8 && (!is_resource($gdImage) || get_resource_type($gdImage) !== 'gd'))
 		){
 			throw new QRCodeDecoderException('Invalid GD image source.'); // @codeCoverageIgnore
@@ -51,6 +51,19 @@ class GDLuminanceSource extends LuminanceSourceAbstract{
 
 		$this->gdImage = $gdImage;
 
+		if($this->options->readerGrayscale){
+			imagefilter($this->gdImage,  IMG_FILTER_GRAYSCALE);
+		}
+
+		if($this->options->readerInvertColors){
+			imagefilter($this->gdImage, IMG_FILTER_NEGATE);
+		}
+
+		if($this->options->readerIncreaseContrast){
+			imagefilter($this->gdImage, IMG_FILTER_BRIGHTNESS, -100);
+			imagefilter($this->gdImage, IMG_FILTER_CONTRAST, -100);
+		}
+
 		$this->setLuminancePixels();
 	}
 
@@ -59,15 +72,6 @@ class GDLuminanceSource extends LuminanceSourceAbstract{
 	 */
 	protected function setLuminancePixels():void{
 
-		if($this->options->readerGrayscale){
-			imagefilter($this->gdImage,  IMG_FILTER_GRAYSCALE);
-		}
-
-		if($this->options->readerIncreaseContrast){
-			imagefilter($this->gdImage, IMG_FILTER_BRIGHTNESS, -100);
-			imagefilter($this->gdImage, IMG_FILTER_CONTRAST, -100);
-		}
-
 		for($j = 0; $j < $this->height; $j++){
 			for($i = 0; $i < $this->width; $i++){
 				$argb  = imagecolorat($this->gdImage, $i, $j);

src/Decoder/IMagickLuminanceSource.php

@@ -33,24 +33,27 @@ class IMagickLuminanceSource extends LuminanceSourceAbstract{
 
 		$this->imagick = $imagick;
 
-		$this->setLuminancePixels();
-	}
-
-	/**
-	 *
-	 */
-	protected function setLuminancePixels():void{
-
 		if($this->options->readerGrayscale){
 			$this->imagick->setImageColorspace(Imagick::COLORSPACE_GRAY);
 		}
 
+		if($this->options->readerInvertColors){
+			$this->imagick->negateImage($this->options->readerGrayscale);
+		}
+
 		if($this->options->readerIncreaseContrast){
 			for($i = 0; $i < 10; $i++){
 				$this->imagick->contrastImage(false); // misleading docs
 			}
 		}
 
+		$this->setLuminancePixels();
+	}
+
+	/**
+	 *
+	 */
+	protected function setLuminancePixels():void{
 		$pixels = $this->imagick->exportImagePixels(1, 1, $this->width, $this->height, 'RGB', Imagick::PIXEL_CHAR);
 		$count  = count($pixels);
 

src/QROptionsTrait.php

@@ -466,6 +466,11 @@ trait QROptionsTrait{
 	 */
 	protected bool $readerGrayscale = false;
 
+	/**
+	 * Invert the colors of the image
+	 */
+	protected bool $readerInvertColors = false;
+
 	/**
 	 * Increase the contrast before reading
 	 *