Method and apparatus for harmonizing multiple sign bit hiding and residual sign prediction

An apparatus for decoding signs of a set of transform coefficients of a signal, the apparatus comprising processing circuitry which is configured to:

• decode an entropy encoded sequence of a first plurality of binary values;
• determine a list of transform coefficients, comprising a first plurality of transform coefficients out of the set of transform coefficients, according to a first predetermined rule;
• select a further transform coefficient, which is out of the set of transform coefficients and not being included in the list, according to a second predetermined rule;
• determine a sign of the further transform coefficient by calculating a predetermined function of transform coefficient values in the set of transform coefficients;
• perform an estimation procedure determining estimated signs, which estimate the corresponding signs, of the transform coefficients in the list;
• and
• correct the estimated signs using the decoded sequence of the first plurality of binary values, so as to obtain the signs of the first plurality of transform coefficients.

A method of encoding signs of a set of transform coefficients of a signal, the method comprising:

• determining a list of transform coefficients, comprising a first plurality of transform coefficients out of the set of transform coefficients, according to a first predetermined rule;
• selecting a further transform coefficient, which is out of the set of transform coefficients and not included in the list, according to a second predetermined rule;
• embedding a sign of the further transform coefficient in a result of a predetermined function of transform coefficient values in the set of transform coefficients;
• performing an estimation procedure determining a respective estimated sign, which estimates a respective sign, of each of the transform coefficients in the list;
• determining, for each transformation coefficient of the first plurality of transform coefficients, a binary value indicating whether or not the respective sign of the transform coefficient coincides with the respective estimated sign of the transform coefficient;
• and
• encoding a sequence of binary values, comprising the binary value determined for each of the first plurality of transform coefficients, using an entropy coding technique.

A method of decoding signs of a set of transform coefficients of a signal, the method comprising the steps of

• decoding an entropy encoded sequence of a first plurality of binary values;
• determining a list of transform coefficients, comprising a first plurality of transform coefficients out of the set of transform coefficients, according to a first predetermined rule;
• selecting a further transform coefficient, which is out of the set of transform coefficients and not included in the list, according to a second predetermined rule;
• determining a sign of the further transform coefficient by calculating a predetermined function of transform coefficient values in the set of transform coefficients;
• performing an estimation procedure determining estimated signs, which estimate the corresponding signs of the transform coefficients in the list;
• and
• correcting the estimated signs by using the decoded sequence of the first plurality of binary values, so as to obtain the signs of the first plurality of transform coefficients.