toJSON( meta ) {

		const isRootObject = ( meta === undefined || typeof meta === 'string' );

		if ( ! isRootObject && meta.images[ this.uuid ] !== undefined ) {

			return meta.images[ this.uuid ];

		}

		const output = {
			uuid: this.uuid,
			url: ''
		};

		const data = this.data;

		if ( data !== null ) {

			let url;

			if ( Array.isArray( data ) ) {

				// cube texture

				url = [];

				for ( let i = 0, l = data.length; i < l; i ++ ) {

					if ( data[ i ].isDataTexture ) {

						url.push( serializeImage( data[ i ].image ) );

					} else {

						url.push( serializeImage( data[ i ] ) );

					}

				}

			} else {

				// texture

				url = serializeImage( data );

			}

			output.url = url;

		}

		if ( ! isRootObject ) {

			meta.images[ this.uuid ] = output;

		}

		return output;

	}
Serializes the source into JSON.

@param {?(Object|string)} meta - An optional value holding meta information about the serialization.
@return {Object} A JSON object representing the serialized source.
@see {@link ObjectLoader#parse}