Image encoding method and device for sample value compensation and image decoding method and device for sample value compensation

An image decoding apparatus comprising:

• an extractor configured to parse offset values and an offset type from a bitstream, and to parse a class based on the offset type from the bitstream;
• an offset determiner configured to select a plurality of pixels from among pixels adjacent to a reconstructed pixel, based on the class, to calculate a reference value based on sample values of the plurality of pixels, to determine a category based on a magnitude of a difference value between the reference value and a sample value of the reconstructed pixel, and to select an offset value from among the offset values, the offset value corresponding to the category;
• and
• a pixel compensator configured to compensate for the sample value of the reconstructed pixel by using the selected offset value.

An image encoding method comprising:

• selecting a plurality of pixels from among pixels adjacent to a reconstructed pixel, based on a class from among a plurality of classes according to an offset type, and calculating a reference value based on sample values of the plurality of pixels;
• determining a category based on a magnitude of a difference value between the reference value and a sample value of the reconstructed pixel;
• determining an offset value corresponding to the category, based on the sample value of the reconstructed pixel and a sample value of an original pixel of the reconstructed pixel;
• encoding the offset value, the offset type, and the class;
• and
• transmitting a bitstream comprising the encoded offset value, the encoded offset type, and the encoded class.