Implement 'indexed' option in PNG encoders

src/Drivers/Gd/Encoders/PngEncoder.php

@@ -4,22 +4,72 @@ declare(strict_types=1);
 
 namespace Intervention\Image\Drivers\Gd\Encoders;
 
+use GdImage;
+use Intervention\Image\Drivers\Gd\Cloner;
 use Intervention\Image\EncodedImage;
 use Intervention\Image\Encoders\PngEncoder as GenericPngEncoder;
+use Intervention\Image\Exceptions\AnimationException;
+use Intervention\Image\Exceptions\ColorException;
+use Intervention\Image\Exceptions\RuntimeException;
 use Intervention\Image\Interfaces\ImageInterface;
 use Intervention\Image\Interfaces\SpecializedInterface;
 
 class PngEncoder extends GenericPngEncoder implements SpecializedInterface
 {
+    /**
+     * {@inheritdoc}
+     *
+     * @see EncoderInterface::encode()
+     */
     public function encode(ImageInterface $image): EncodedImage
     {
-        $gd = $image->core()->native();
+        $output = $this->prepareOutput($image);
-        $data = $this->buffered(function () use ($gd) {
+
-            imageinterlace($gd, $this->interlaced);
+        // encode
-            imagepng($gd, null, -1);
+        $data = $this->buffered(function () use ($output) {
-            imageinterlace($gd, false);
+            imageinterlace($output, $this->interlaced);
+            imagepng($output, null, -1);
         });
 
         return new EncodedImage($data, 'image/png');
     }
+
+    /**
+     * Prepare given image instance for PNG format output according to encoder settings
+     *
+     * @param ImageInterface $image
+     * @param bool $indexed
+     * @throws RuntimeException
+     * @throws ColorException
+     * @throws AnimationException
+     * @return GdImage
+     */
+    private function prepareOutput(ImageInterface $image): GdImage
+    {
+        if ($this->indexed === false) {
+            return Cloner::clone($image->core()->native());
+        }
+
+        // get blending color
+        $blendingColor =  $this->driver()->colorProcessor($image->colorspace())->colorToNative(
+            $this->driver()->handleInput($this->driver()->config()->blendingColor)
+        );
+
+        // clone output instance
+        $output = Cloner::cloneEmpty($image->core()->native());
+
+        // fill with blending color
+        imagefill($output, 0, 0, $blendingColor);
+
+        // set transparency
+        imagecolortransparent($output, $blendingColor);
+
+        // copy original into output
+        imagecopy($output, $image->core()->native(), 0, 0, 0, 0, imagesx($output), imagesy($output));
+
+        // reduce to indexed color palette
+        imagetruecolortopalette($output, true, 255);
+
+        return $output;
+    }
 }

src/Drivers/Imagick/Encoders/PngEncoder.php

@@ -5,28 +5,79 @@ declare(strict_types=1);
 namespace Intervention\Image\Drivers\Imagick\Encoders;
 
 use Imagick;
+use ImagickException;
 use Intervention\Image\EncodedImage;
 use Intervention\Image\Encoders\PngEncoder as GenericPngEncoder;
+use Intervention\Image\Exceptions\AnimationException;
+use Intervention\Image\Exceptions\RuntimeException;
+use Intervention\Image\Exceptions\ColorException;
 use Intervention\Image\Interfaces\ImageInterface;
 use Intervention\Image\Interfaces\SpecializedInterface;
 
 class PngEncoder extends GenericPngEncoder implements SpecializedInterface
 {
+    /**
+     * {@inheritdoc}
+     *
+     * @see EncoderInterface::encode()
+     */
     public function encode(ImageInterface $image): EncodedImage
     {
-        $format = 'PNG';
+        $output = $this->prepareOutput($image);
-        $compression = Imagick::COMPRESSION_ZIP;
 
-        $imagick = $image->core()->native();
+        $output->setCompression(Imagick::COMPRESSION_ZIP);
-        $imagick->setFormat($format);
+        $output->setImageCompression(Imagick::COMPRESSION_ZIP);
-        $imagick->setImageFormat($format);
-        $imagick->setCompression($compression);
-        $imagick->setImageCompression($compression);
 
         if ($this->interlaced) {
-            $imagick->setInterlaceScheme(Imagick::INTERLACE_LINE);
+            $output->setInterlaceScheme(Imagick::INTERLACE_LINE);
         }
 
-        return new EncodedImage($imagick->getImagesBlob(), 'image/png');
+        return new EncodedImage($output->getImagesBlob(), 'image/png');
+    }
+
+    /**
+     * Prepare given image instance for PNG format output according to encoder settings
+     *
+     * @param ImageInterface $image
+     * @throws AnimationException
+     * @throws RuntimeException
+     * @throws ColorException
+     * @throws ImagickException
+     * @return Imagick
+     */
+    private function prepareOutput(ImageInterface $image): Imagick
+    {
+        if ($this->indexed === false) {
+            $output = clone $image->core()->native();
+
+            // ensure to encode PNG image type 6 true color alpha
+            $output->setFormat('PNG32');
+            $output->setImageFormat('PNG32');
+
+            return $output;
+        }
+
+        // get blending color
+        $blendingColor =  $this->driver()->colorProcessor($image->colorspace())->colorToNative(
+            $this->driver()->handleInput($this->driver()->config()->blendingColor)
+        );
+
+        // create new image with blending color as background
+        $output = new Imagick();
+        $output->newImage($image->width(), $image->height(), $blendingColor, 'PNG');
+
+        // set transparency of original image
+        $output->compositeImage($image->core()->native(), Imagick::COMPOSITE_DSTIN, 0, 0);
+        $output->transparentPaintImage('#000000', 0, 0, false);
+
+        // copy original and create indexed color palette version
+        $output->compositeImage($image->core()->native(), Imagick::COMPOSITE_DEFAULT, 0, 0);
+        $output->quantizeImage(255, $output->getImageColorSpace(), 0, false, false);
+
+        // ensure to encode PNG image type 3 (indexed)
+        $output->setFormat('PNG8');
+        $output->setImageFormat('PNG8');
+
+        return $output;
     }
 }

src/Encoders/PngEncoder.php

@@ -8,7 +8,7 @@ use Intervention\Image\Drivers\SpecializableEncoder;
 
 class PngEncoder extends SpecializableEncoder
 {
-    public function __construct(public bool $interlaced = false)
+    public function __construct(public bool $interlaced = false, public bool $indexed = false)
     {
     }
 }