Media: fix degraded handling for 24 bit PNG uploads.

Add additional logic to correctly identify indexed PNG images so output PNGs correctly  match the uploaded image depth.

Fix a regression introduced in WordPress 6.8 [59589] where uploaded Truecolor PNG images (meaning > 8 bit) were mis-identified as indexed (8 bit) images, causing output images to be indexed instead of Truecolor resulting in a noticeable visual degradation. 

Props elvismdev, wildworks, SirLouen, siliconforks, joemcgill, iamshashank, nosilver4u.
Fixes #63448.




git-svn-id: https://develop.svn.wordpress.org/trunk@60246 602fd350-edb4-49c9-b593-d223f7449a82

1 files changed, 21 insertions, 30 deletions

diff --git a/src/wp-includes/class-wp-image-editor-imagick.php b/src/wp-includes/class-wp-image-editor-imagick.php
index 66085ac503..2e7c7039d5 100644
--- a/src/wp-includes/class-wp-image-editor-imagick.php
+++ b/src/wp-includes/class-wp-image-editor-imagick.php
@@ -484,37 +484,28 @@ class WP_Image_Editor_Imagick extends WP_Image_Editor {
 				$this->image->setOption( 'png:compression-filter', '5' );
 				$this->image->setOption( 'png:compression-level', '9' );
 				$this->image->setOption( 'png:compression-strategy', '1' );
-				// Check to see if a PNG is indexed, and find the pixel depth.
-				if ( is_callable( array( $this->image, 'getImageDepth' ) ) ) {
-					$indexed_pixel_depth = $this->image->getImageDepth();
-
-					// Indexed PNG files get some additional handling.
-					if ( 0 < $indexed_pixel_depth && 8 >= $indexed_pixel_depth ) {
-						// Check for an alpha channel.
-						if (
-							is_callable( array( $this->image, 'getImageAlphaChannel' ) )
-							&& $this->image->getImageAlphaChannel()
-						) {
-							$this->image->setOption( 'png:include-chunk', 'tRNS' );
-						} else {
-							$this->image->setOption( 'png:exclude-chunk', 'all' );
-						}
-
-						// Reduce colors in the images to maximum needed, using the global colorspace.
-						$max_colors = pow( 2, $indexed_pixel_depth );
-						if ( is_callable( array( $this->image, 'getImageColors' ) ) ) {
-							$current_colors = $this->image->getImageColors();
-							$max_colors     = min( $max_colors, $current_colors );
-						}
-						$this->image->quantizeImage( $max_colors, $this->image->getColorspace(), 0, false, false );
-
-						/**
-						 * If the colorspace is 'gray', use the png8 format to ensure it stays indexed.
-						 */
-						if ( Imagick::COLORSPACE_GRAY === $this->image->getImageColorspace() ) {
-							$this->image->setOption( 'png:format', 'png8' );
-						}
+
+				// Indexed PNG files get some additional handling.
+				// See #63448 for details.
+				if (
+					is_callable( array( $this->image, 'getImageProperty' ) )
+					&& '3' === $this->image->getImageProperty( 'png:IHDR.color-type-orig' )
+				) {
+
+					// Check for an alpha channel.
+					if (
+						is_callable( array( $this->image, 'getImageAlphaChannel' ) )
+						&& $this->image->getImageAlphaChannel()
+					) {
+						$this->image->setOption( 'png:include-chunk', 'tRNS' );
+					} else {
+						$this->image->setOption( 'png:exclude-chunk', 'all' );
 					}
+					// Set the image format to Indexed PNG.
+					$this->image->setOption( 'png:format', 'png8' );
+
+				} else {
+					$this->image->setOption( 'png:exclude-chunk', 'all' );
 				}
 			}