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Media: Adjust PDF upload handling to remove non-opaque alpha channels from previews.

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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.


git-svn-id: https://develop.svn.wordpress.org/trunk@56271 602fd350-edb4-49c9-b593-d223f7449a82
This commit is contained in:
Anthony Burchell
2023-07-19 22:33:47 +00:00
parent 6281ce432c
commit 287fd501f2
3 changed files with 72 additions and 0 deletions
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22
src/wp-includes/class-wp-image-editor-imagick.php
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@@ -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.

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tests/phpunit/data/images/test-alpha.pdf Normal file
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50
tests/phpunit/tests/image/editorImagick.php
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@@ -641,4 +641,54 @@ class Tests_Image_Editor_Imagick extends WP_Image_UnitTestCase {
$this->assertNotWPError( $saved );
}
/**
* Tests that the alpha channel of PDFs is removed from PDF previews.
*
* Only affects systems with Ghostscript version >= 9.14.
*
* @ticket 39216
*
* @covers WP_Image_Editor_Imagick::remove_pdf_alpha_channel
*/
public function test_remove_pdf_alpha_channel_should_remove_the_alpha_channel_in_preview() {
if ( ! wp_image_editor_supports( array( 'mime_type' => 'application/pdf' ) ) ) {
$this->markTestSkipped( 'Rendering PDFs is not supported on this system.' );
}
$test_file = DIR_TESTDATA . '/images/test-alpha.pdf';
$attachment_id = $this->factory->attachment->create_upload_object( $test_file );
$this->assertNotEmpty( $attachment_id, 'The attachment was not created before testing.' );
$attached_file = get_attached_file( $attachment_id );
$this->assertNotEmpty( $attached_file, 'The attached file was not returned.' );
$rgb = array(
'r' => true,
'g' => true,
'b' => true,
);
// White.
$expected = array(
'r' => 1,
'g' => 1,
'b' => 1,
);
$check = image_get_intermediate_size( $attachment_id, 'full' );
$this->assertIsArray( $check, 'The intermediate size could not be retrieved.' );
$this->assertArrayHasKey( 'file', $check, 'The intermediate size file was not found.' );
$check_file = path_join( dirname( $attached_file ), $check['file'] );
$imagick = new Imagick( $check_file );
$output = array_map(
static function( $value ) {
return (int) round( $value );
},
array_intersect_key( $imagick->getImagePixelColor( 100, 100 )->getColor( true /* normalized */ ), $rgb )
);
$imagick->destroy();
$this->assertSame( $expected, $output, 'The image color of the generated thumb does not match expected opaque background.' ); // Allow for floating point equivalence.
}
}