Method and device for encoding at least one image unit, and method and device for decoding a stream representative of at least one image unit

A method for decoding a stream representative of at least one image unit, comprising:

• decoding said stream to obtain at least one reconstructed image unit,
• applying a sample adaptive offset filter to said at least one reconstructed image unit;
• wherein applying a sample adaptive offset filter to said at least one reconstructed image unit comprises:
• determining at least one current category in a set of categories for at least one pixel of the reconstructed image unit,
• decoding an offset value for at least one category of said set of categories;
• determining said current category is equal to said category having said decoded offset value, and
• in response thereto applying a pre-filter to the at least one pixel of the reconstructed image unit assigned to said category,
• wherein, for a pixel of the reconstructed image unit to be pre-filtered, said pre-filter is a median filter taking into account all of the pixels of a filtering window inside the reconstructed image unit assigned to a category having an associated decoded offset value;
• adding said decoded offset value to said at least one pixel of the reconstructed image unit.

A device for encoding at least one image unit, comprising at least one processor configured to:

• encode said at least one image unit, reconstruct said at least one image unit into at least one reconstructed image unit,
• apply a sample adaptive offset filter to said at least one reconstructed image unit;
• wherein said at least one processor configured to apply a sample adaptive offset filter to said at least one reconstructed image unit is also configured to:
• determine at least one current category in a set of categories for at least one pixel of the reconstructed image unit, encode an offset value for at least one category of said set of categories;
• determine that said current category is equal to said category having an encoded offset value, and
• in response thereto apply a pre-filter to the at least one pixel of the reconstructed image unit assigned to said category,
• wherein, for a pixel of the reconstructed image unit to be pre-filtered, said pre-filter is a median filter taking into account all of the pixels of a filtering window inside the reconstructed image unit assigned to a category having an associated encoded offset value;
• add said encoded offset value to said at least one pixel of the reconstructed image unit.

A device for decoding a stream representative of at least one image unit, comprising at least one processor configured to:

• decode said stream to obtain at least one reconstructed image unit,
• apply a sample adaptive offset filter to said at least one reconstructed image unit;
• wherein said at least one processor configured to apply a sample adaptive offset filter to said at least one reconstructed image unit is also configured to:
• determine at least one current category in a set of categories for at least one pixel of the reconstructed image unit, decode an offset value for at least one category of said set of categories;
• determine that said current category is equal to said category having a decoded offset value, and
• in response thereto apply a pre-filter to the at least one pixel of the reconstructed image unit assigned to said category,
• wherein, for a pixel of the reconstructed image unit to be pre-filtered, said pre-filter is a median filter taking into account all of the pixels of a filtering window inside the reconstructed image unit assigned to a category having an associated decoded offset value;
• add said decoded offset value to said at least one pixel of the reconstructed image unit.