An image forming apparatus applies a dither matrix to multi-valued image data. The outer diameter is less than 110 an operating wavelength, and preferably about 120th, so that the antenna is electrically small relative to the wavelength. The system further comprises a processor configured to measure, for each sub-image, two linear coefficients corresponding to a local wavefront aberration of the sub-image and to estimate, for each sub-image, three quadratic coefficients corresponding to the local wavefront aberration of the sub-image. A cylinder is disposed in the cylinder block and the cylinder head. One or more additional substrate processing steps are performed without an interruption in the plasma between the first substrate processing step and the one or more additional substrate processing steps.