diff --git a/src/wp-includes/class-wp-image-editor.php b/src/wp-includes/class-wp-image-editor.php
index e7070b1ca6..fed0fc16e8 100644
--- a/src/wp-includes/class-wp-image-editor.php
+++ b/src/wp-includes/class-wp-image-editor.php
@@ -414,8 +414,8 @@ abstract class WP_Image_Editor {
 			// The image will be converted when saving. Set the quality for the new mime-type if not already set.
 			if ( $mime_type !== $this->output_mime_type ) {
 				$this->output_mime_type = $mime_type;
-				$this->set_quality();
 			}
+			$this->set_quality();
 		} elseif ( ! empty( $this->output_mime_type ) ) {
 			// Reset output_mime_type and quality.
 			$this->output_mime_type = null;
diff --git a/tests/phpunit/tests/image/editor.php b/tests/phpunit/tests/image/editor.php
index 487dad0664..be4591451d 100644
--- a/tests/phpunit/tests/image/editor.php
+++ b/tests/phpunit/tests/image/editor.php
@@ -105,9 +105,6 @@ class Tests_Image_Editor extends WP_Image_UnitTestCase {
 
 		// Ensure wp_editor_set_quality filter applies if it exists before editor instantiation.
 		$this->assertSame( 100, $editor->get_quality() );
-
-		// Clean up.
-		remove_filter( 'wp_editor_set_quality', $func_100_percent );
 	}
 
 	/**
@@ -119,18 +116,25 @@ class Tests_Image_Editor extends WP_Image_UnitTestCase {
 		$editor = wp_get_image_editor( DIR_TESTDATA . '/images/test-image.png' );
 		$editor->set_mime_type( 'image/png' ); // Ensure mime-specific filters act properly.
 
+		// Quality setting for the source image. For PNG the fallback default of 82 is used.
+		$this->assertSame( 82, $editor->get_quality(), 'Default quality setting is 82.' );
+
 		// Set conversions for uploaded images.
 		add_filter( 'image_editor_output_format', array( $this, 'image_editor_output_formats' ) );
 
 		// Quality setting for the source image. For PNG the fallback default of 82 is used.
 		$this->assertSame( 82, $editor->get_quality(), 'Default quality setting is 82.' );
 
-		// Quality should change to the output format's value.
-		// A PNG image will be converted to WEBP whose quialty should be 86.
+		// When saving, quality should change to the output format's value.
+		// A PNG image will be converted to WebP whose quality should be 86.
 		$editor->save();
-		$this->assertSame( 86, $editor->get_quality(), 'Output image format is WEBP. Quality setting for it should be 86.' );
+		$this->assertSame( 86, $editor->get_quality(), 'Output image format is WebP. Quality setting for it should be 86.' );
 
-		// Removing PNG to WEBP conversion on save. Quality setting should reset to the default.
+		// Saving again should not change the quality.
+		$editor->save();
+		$this->assertSame( 86, $editor->get_quality(), 'Output image format is WebP. Quality setting for it should be 86.' );
+
+		// Removing PNG to WebP conversion on save. Quality setting should reset to the default.
 		remove_filter( 'image_editor_output_format', array( $this, 'image_editor_output_formats' ) );
 		$editor->save();
 		$this->assertSame( 82, $editor->get_quality(), 'After removing image conversion quality setting should reset to the default of 82.' );
@@ -149,9 +153,9 @@ class Tests_Image_Editor extends WP_Image_UnitTestCase {
 		$this->assertSame( 56, $editor->get_quality(), 'Filtered default quality for JPEG is 56.' );
 
 		// Quality should change to the output format's value as filtered above.
-		// A JPEG image will be converted to WEBP whose quialty should be 42.
+		// A JPEG image will be converted to WebP whose quialty should be 42.
 		$editor->save();
-		$this->assertSame( 42, $editor->get_quality(), 'Image conversion from JPEG to WEBP. Filtered WEBP quality shoild be 42.' );
+		$this->assertSame( 42, $editor->get_quality(), 'Image conversion from JPEG to WEBP. Filtered WEBP quality should be 42.' );
 
 		// After removing the conversion the quality setting should reset to the filtered value for the original image type, JPEG.
 		remove_filter( 'image_editor_output_format', array( $this, 'image_editor_output_formats' ) );
@@ -161,8 +165,6 @@ class Tests_Image_Editor extends WP_Image_UnitTestCase {
 			$editor->get_quality(),
 			'After removing image conversion the quality setting should reset to the filtered value for JPEG, 56.'
 		);
-
-		remove_filter( 'wp_editor_set_quality', array( $this, 'image_editor_change_quality' ) );
 	}
 
 	/**
diff --git a/tests/phpunit/tests/media.php b/tests/phpunit/tests/media.php
index 820da7ed3d..0d5ac75863 100644
--- a/tests/phpunit/tests/media.php
+++ b/tests/phpunit/tests/media.php
@@ -3621,6 +3621,97 @@ EOF;
 		// Clean up the above filter.
 		remove_filter( 'wp_omit_loading_attr_threshold', '__return_null', 100 );
 	}
+
+	/**
+	 * Test that generated files with the `image_editor_output_format` applied use the correct
+	 * quality level based on their mime type.
+	 *
+	 * @ticket 56442
+	 */
+	public function test_quality_with_image_conversion_file_sizes() {
+		add_filter( 'image_editor_output_format', array( $this, 'image_editor_output_jpeg' ) );
+		$temp_dir = get_temp_dir();
+		$file     = $temp_dir . '/33772.jpg';
+		copy( DIR_TESTDATA . '/images/33772.jpg', $file );
+
+		// Set JPEG output quality very low and WebP quality very high, this should force all generated WebP images to
+		// be larger than the the matching generated JPEGs.
+		add_filter( 'wp_editor_set_quality', array( $this, 'image_editor_change_quality_low_jpeg' ), 10, 2 );
+
+		$editor = wp_get_image_editor( $file );
+
+		// Verify that the selected editor supports WebP output.
+		if ( ! $editor->supports_mime_type( 'image/webp' ) ) {
+			$this->markTestSkipped( 'WebP is not supported by the selected image editor.' );
+		}
+
+		$attachment_id = self::factory()->attachment->create_object(
+			array(
+				'post_mime_type' => 'image/jpeg',
+				'file'           => $file,
+			)
+		);
+
+		add_filter( 'big_image_size_threshold', array( $this, 'add_big_image_size_threshold' ) );
+
+		// Generate all sizes as JPEGs.
+		$jpeg_sizes = wp_generate_attachment_metadata( $attachment_id, $file );
+		remove_filter( 'image_editor_output_format', array( $this, 'image_editor_output_jpeg' ) );
+
+		// Generate all sizes as WebP.
+		add_filter( 'image_editor_output_format', array( $this, 'image_editor_output_webp' ) );
+		$webp_sizes = wp_generate_attachment_metadata( $attachment_id, $file );
+		remove_filter( 'image_editor_output_format', array( $this, 'image_editor_output_webp' ) );
+
+		// The main (scaled) image: the JPEG should be smaller than the WebP.
+		$this->assertLessThan( $webp_sizes['filesize'], $jpeg_sizes['filesize'], 'The JPEG should be smaller than the WebP.' );
+
+		// Sub-sizes: for each size, the JPEGs should be smaller than the WebP.
+		$sizes_to_compare = array_intersect_key( $jpeg_sizes['sizes'], $webp_sizes['sizes'] );
+		foreach ( $sizes_to_compare as $size => $size_data ) {
+			$this->assertLessThan( $webp_sizes['sizes'][ $size ]['filesize'], $jpeg_sizes['sizes'][ $size ]['filesize'] );
+		}
+	}
+
+	/**
+	 * Add threshold to create a `-scaled` output image for testing.
+	 */
+	public function add_big_image_size_threshold() {
+		return 1000;
+	}
+
+	/**
+	 * Output JPEG files.
+	 */
+	public function image_editor_output_jpeg() {
+		return array( 'image/jpeg' => 'image/jpeg' );
+	}
+
+	/**
+	 * Output WebP files.
+	 */
+	public function image_editor_output_webp() {
+		return array( 'image/jpeg' => 'image/webp' );
+	}
+
+	/**
+	 * Changes the quality using very low quality for JPEGs and very high quality
+	 * for WebPs, used to verify the filter is applying correctly.
+	 *
+	 * @param int    $quality   Default quality.
+	 * @param string $mime_type Image mime-type.
+	 * @return int The changed quality.
+	 */
+	public function image_editor_change_quality_low_jpeg( $quality, $mime_type ) {
+		if ( 'image/jpeg' === $mime_type ) {
+			return 1;
+		} elseif ( 'image/webp' === $mime_type ) {
+			return 100;
+		} else {
+			return 30;
+		}
+	}
+
 }
 
 /**