From cc3652efe9a78c732d4c61d5d85f04ab64e10343 Mon Sep 17 00:00:00 2001
From: antpb <antpb@git.wordpress.org>
Date: Wed, 19 Jul 2023 22:35:27 +0000
Subject: [PATCH] Media: Adjust PDF upload handling to remove non-opaque alpha
 channels from previews.

Previously, Imagick uploads of PDF files with non-opaque alpha channels would result in a black background replacing alpha in the generated thumbnail. This patch adds a `remove_pdf_alpha_channel()` function in the Imagick classes to use a white background instead.

Props gitlost, joemcgill, joedolson, launchinteractive, emirpprime, mwtsn, ceer, maysi, madejackson, 6adminit, costdev, oglekler.
Fixes #39216.

Built from https://develop.svn.wordpress.org/trunk@56271


git-svn-id: http://core.svn.wordpress.org/trunk@55783 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/class-wp-image-editor-imagick.php | 22 +++++++++++++++++++
 wp-includes/version.php                       |  2 +-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/wp-includes/class-wp-image-editor-imagick.php b/wp-includes/class-wp-image-editor-imagick.php
index 756fcce894..f29373f253 100644
--- a/wp-includes/class-wp-image-editor-imagick.php
+++ b/wp-includes/class-wp-image-editor-imagick.php
@@ -168,6 +168,10 @@ class WP_Image_Editor_Imagick extends WP_Image_Editor {
 				$this->image->setIteratorIndex( 0 );
 			}
 
+			if ( 'pdf' === $file_extension ) {
+				$this->remove_pdf_alpha_channel();
+			}
+
 			$this->mime_type = $this->get_mime_type( $this->image->getImageFormat() );
 		} catch ( Exception $e ) {
 			return new WP_Error( 'invalid_image', $e->getMessage(), $this->file );
@@ -751,6 +755,24 @@ class WP_Image_Editor_Imagick extends WP_Image_Editor {
 		return $saved;
 	}
 
+	/**
+	 * Removes PDF alpha after it's been read.
+	 *
+	 * @since 6.4.0
+	 */
+	protected function remove_pdf_alpha_channel() {
+		$version = Imagick::getVersion();
+		// Remove alpha channel if possible to avoid black backgrounds for Ghostscript >= 9.14. RemoveAlphaChannel added in ImageMagick 6.7.5.
+		if ( $version['versionNumber'] >= 0x675 ) {
+			try {
+				// Imagick::ALPHACHANNEL_REMOVE mapped to RemoveAlphaChannel in PHP imagick 3.2.0b2.
+				$this->image->setImageAlphaChannel( defined( 'Imagick::ALPHACHANNEL_REMOVE' ) ? Imagick::ALPHACHANNEL_REMOVE : 12 );
+			} catch ( Exception $e ) {
+				return new WP_Error( 'pdf_alpha_process_failed', $e->getMessage() );
+			}
+		}
+	}
+
 	/**
 	 * @since 3.5.0
 	 * @since 6.0.0 The `$filesize` value was added to the returned array.
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 89c095943c..8ae67197d0 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-alpha-56270';
+$wp_version = '6.4-alpha-56271';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.