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Media: Prevent Imagick pre-sampling from upscaling images #12520

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Media: Prevent Imagick pre-sampling from upscaling images #12520

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19 changes: 14 additions & 5 deletions src/wp-includes/class-wp-image-editor-imagick.php
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Original file line number Diff line number Diff line change
Expand Up @@ -492,15 +492,24 @@ protected function thumbnail_image( $dst_w, $dst_h, $filter_name = 'FILTER_TRIAN

/*
* To be more efficient, resample large images to 5x the destination size before resizing
* whenever the output size is less that 1/3 of the original image size (1/3^2 ~= .111),
* unless we would be resampling to a scale smaller than 128x128.
* whenever the output size is less than 1/3 of the original image size (1/3^2 ~= 0.111),
* but only when resampling reduces both source dimensions and keeps both dimensions above 128px.
*/
if ( is_callable( array( $this->image, 'sampleImage' ) ) ) {
$resize_ratio = ( $dst_w / $this->size['width'] ) * ( $dst_h / $this->size['height'] );
$source_size = $this->image->getImageGeometry();
$resize_ratio = ( $dst_w / $source_size['width'] ) * ( $dst_h / $source_size['height'] );
$sample_factor = 5;
$sample_width = $dst_w * $sample_factor;
$sample_height = $dst_h * $sample_factor;

if ( $resize_ratio < .111 && ( $dst_w * $sample_factor > 128 && $dst_h * $sample_factor > 128 ) ) {
$this->image->sampleImage( $dst_w * $sample_factor, $dst_h * $sample_factor );
if (
$resize_ratio < 0.111
&& $sample_width > 128
&& $sample_height > 128
&& $sample_width < $source_size['width']
&& $sample_height < $source_size['height']
) {
$this->image->sampleImage( $sample_width, $sample_height );
}
}

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93 changes: 93 additions & 0 deletions tests/phpunit/tests/image/editorImagick.php
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Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,99 @@ public function test_resize() {
);
}

/**
* Tests that pre-sampling does not upscale the source image.
*
* @ticket 48842
*/
public function test_thumbnail_image_presampling_does_not_upscale() {
$image = new class() {
public $source_size;
public $sample_size;

// phpcs:disable WordPress.NamingConventions.ValidFunctionName.MethodNameInvalid
public function getImageGeometry() {
return $this->source_size;
}

public function sampleImage( $width, $height ) {
$this->sample_size = array( $width, $height );
}

public function scaleImage() {
}
// phpcs:enable
};

$editor = new class( null ) extends WP_Image_Editor_Imagick {
public function call_thumbnail_image( $image, $source_size, $editor_size, $destination_size ) {
$image->source_size = array(
'width' => $source_size[0],
'height' => $source_size[1],
);
$image->sample_size = null;
$this->image = $image;
$this->size = array(
'width' => $editor_size[0],
'height' => $editor_size[1],
);

$result = $this->thumbnail_image( $destination_size[0], $destination_size[1], 'FILTER_TRIANGLE', false );

return is_wp_error( $result ) ? $result : $image->sample_size;
}
};

// The ticket's source and destination dimensions must not trigger an upscale.
$this->assertNull(
$editor->call_thumbnail_image(
$image,
array( 10315, 7049 ),
array( 10315, 7049 ),
array( 2560, 1750 )
)
);

// Use current geometry because cropping can make the editor's stored size stale.
$this->assertNull(
$editor->call_thumbnail_image(
$image,
array( 200, 1000 ),
array( 1000, 1000 ),
array( 50, 100 )
)
);

// Skip pre-sampling unless both intermediate dimensions are smaller than the source.
$this->assertNull(
$editor->call_thumbnail_image(
$image,
array( 1500, 1000 ),
array( 1500, 1000 ),
array( 300, 150 )
)
);
$this->assertNull(
$editor->call_thumbnail_image(
$image,
array( 2000, 750 ),
array( 2000, 750 ),
array( 300, 150 )
)
);

// Keep pre-sampling when both intermediate dimensions are smaller than the source.
$this->assertSame(
array( 1500, 750 ),
$editor->call_thumbnail_image(
$image,
array( 4800, 2400 ),
array( 4800, 2400 ),
array( 300, 150 )
)
);
}

/**
* Tests multi_resize() with single image resize and no crop.
*/
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