Source

File: wp-admin/includes/image.php

function wp_create_image_subsizes( $file, $attachment_id ) {
	$imagesize = @getimagesize( $file );

	if ( empty( $imagesize ) ) {
		// File is not an image.
		return array();
	}

	// Default image meta.
	$image_meta = array(
		'width'  => $imagesize[0],
		'height' => $imagesize[1],
		'file'   => _wp_relative_upload_path( $file ),
		'sizes'  => array(),
	);

	// Fetch additional metadata from EXIF/IPTC.
	$exif_meta = wp_read_image_metadata( $file );

	if ( $exif_meta ) {
		$image_meta['image_meta'] = $exif_meta;
	}

	// Do not scale (large) PNG images. May result in sub-sizes that have greater file size than the original. See #48736.
	if ( 'image/png' !== $imagesize['mime'] ) {

		/**
		 * Filters the "BIG image" threshold value.
		 *
		 * If the original image width or height is above the threshold, it will be scaled down. The threshold is
		 * used as max width and max height. The scaled down image will be used as the largest available size, including
		 * the `_wp_attached_file` post meta value.
		 *
		 * Returning `false` from the filter callback will disable the scaling.
		 *
		 * @since 5.3.0
		 *
		 * @param int    $threshold     The threshold value in pixels. Default 2560.
		 * @param array  $imagesize     {
		 *     Indexed array of the image width and height in pixels.
		 *
		 *     @type int $0 The image width.
		 *     @type int $1 The image height.
		 * }
		 * @param string $file          Full path to the uploaded image file.
		 * @param int    $attachment_id Attachment post ID.
		 */
		$threshold = (int) apply_filters( 'big_image_size_threshold', 2560, $imagesize, $file, $attachment_id );

		// If the original image's dimensions are over the threshold,
		// scale the image and use it as the "full" size.
		if ( $threshold && ( $image_meta['width'] > $threshold || $image_meta['height'] > $threshold ) ) {
			$editor = wp_get_image_editor( $file );

			if ( is_wp_error( $editor ) ) {
				// This image cannot be edited.
				return $image_meta;
			}

			// Resize the image.
			$resized = $editor->resize( $threshold, $threshold );
			$rotated = null;

			// If there is EXIF data, rotate according to EXIF Orientation.
			if ( ! is_wp_error( $resized ) && is_array( $exif_meta ) ) {
				$resized = $editor->maybe_exif_rotate();
				$rotated = $resized;
			}

			if ( ! is_wp_error( $resized ) ) {
				// Append "-scaled" to the image file name. It will look like "my_image-scaled.jpg".
				// This doesn't affect the sub-sizes names as they are generated from the original image (for best quality).
				$saved = $editor->save( $editor->generate_filename( 'scaled' ) );

				if ( ! is_wp_error( $saved ) ) {
					$image_meta = _wp_image_meta_replace_original( $saved, $file, $image_meta, $attachment_id );

					// If the image was rotated update the stored EXIF data.
					if ( true === $rotated && ! empty( $image_meta['image_meta']['orientation'] ) ) {
						$image_meta['image_meta']['orientation'] = 1;
					}
				} else {
					// TODO: Log errors.
				}
			} else {
				// TODO: Log errors.
			}
		} elseif ( ! empty( $exif_meta['orientation'] ) && 1 !== (int) $exif_meta['orientation'] ) {
			// Rotate the whole original image if there is EXIF data and "orientation" is not 1.

			$editor = wp_get_image_editor( $file );

			if ( is_wp_error( $editor ) ) {
				// This image cannot be edited.
				return $image_meta;
			}

			// Rotate the image.
			$rotated = $editor->maybe_exif_rotate();

			if ( true === $rotated ) {
				// Append `-rotated` to the image file name.
				$saved = $editor->save( $editor->generate_filename( 'rotated' ) );

				if ( ! is_wp_error( $saved ) ) {
					$image_meta = _wp_image_meta_replace_original( $saved, $file, $image_meta, $attachment_id );

					// Update the stored EXIF data.
					if ( ! empty( $image_meta['image_meta']['orientation'] ) ) {
						$image_meta['image_meta']['orientation'] = 1;
					}
				} else {
					// TODO: Log errors.
				}
			}
		}
	}

	/*
	 * Initial save of the new metadata.
	 * At this point the file was uploaded and moved to the uploads directory
	 * but the image sub-sizes haven't been created yet and the `sizes` array is empty.
	 */
	wp_update_attachment_metadata( $attachment_id, $image_meta );

	$new_sizes = wp_get_registered_image_subsizes();

	/**
	 * Filters the image sizes automatically generated when uploading an image.
	 *
	 * @since 2.9.0
	 * @since 4.4.0 Added the `$image_meta` argument.
	 * @since 5.3.0 Added the `$attachment_id` argument.
	 *
	 * @param array $new_sizes     Associative array of image sizes to be created.
	 * @param array $image_meta    The image meta data: width, height, file, sizes, etc.
	 * @param int   $attachment_id The attachment post ID for the image.
	 */
	$new_sizes = apply_filters( 'intermediate_image_sizes_advanced', $new_sizes, $image_meta, $attachment_id );

	return _wp_make_subsizes( $new_sizes, $file, $image_meta, $attachment_id );
}