Abstract: A correspondence relation between a structure of a bi-level pattern A and a structure of a bi-level pattern B is statistically learned by use of a learning high-density image. The bi-level pattern A forms a partial region of a low-density character and line image except a screened dot image. The bi-level pattern B forms a corresponding partial region of a desired high-density image. A judgement is made as to whether the low-density image is equal to or different from a screened dot image. Reference pixels are selected from the partial region of the low-density image. The low-density bi-level pattern A is converted into the high-density bi-level pattern B on the basis of a result of the learning by use of the selected reference pixels when the low-density image is different from a screened dot image. A pixel of the low-density image is repeated to convert the low-density image into the high-density image when the low-density image is equal to a screend dot image.

Abstract: A four-way valve for reversible refrigeration cycle. It comprises a casing, a delivery tube in communication with a compressor and opening into the casing, a suction tube in communication with the compressor and opening into the casing, a pair of tubes in communication with two heat exchangers respectively, and opening into the casing one on each side of the suction tube, valve means for communicating the suction tube selectively with either one of the pair of tubes; and a two-way pilot valve mounted longitudinally to the casing. The two-way valve longitudinally mounted to the valve body of the reversible valve permits its vertical installment, thus remarkably reducing horizontal space required therefor.

Abstract: An electromagnetic pilot type valve having at least one auxiliary pilot valve disposed and operatively connected between the pilot valve and the main valve. The auxiliary valve is operated in response to the pilot valve to operate the main valve. With this construction a main valve body of a relatively large diameter can be operated with a small electromagnetic pilot valve, so that the whole construction of the valve can be compactly made.