Method and apparatus for detecting blocks suitable for multiple sign bit hiding

Apparatus for decoding a sign of a current transform coefficient of a signal, the apparatus comprising a processing circuitry configured to:

• determine whether or not the sign of the current transform coefficient is to be derived from a value of a first function of transform coefficients in a set of transform coefficients by evaluating a second function of transform coefficient values in the set of transform coefficients and a number of those transform coefficients in the set of transform coefficients which are larger than a coefficient value threshold;
• and
• derive the sign of the current transform coefficient according to the result of the determination.

Method for encoding a sign of a current transform coefficient of a signal, the method comprising:

• determining whether or not the sign of the current transform coefficient is to be embedded in a result of a first function of transform coefficients in a set of transform coefficients by evaluating a second function of transform coefficient values in the set of transform coefficients and a number of those transform coefficients in the set of transform coefficients which are larger than a coefficient value threshold;
• and
• embedding the sign of the current transform coefficient according to a result of the determination.

Method for decoding a sign of a current transform coefficient of a signal, the method comprising:

• determining whether or not the sign of the current transform coefficient is to be derived from a value of a first function of transform coefficients in a set of transform coefficients by evaluating a second function of transform coefficient values in the set of transform coefficients and a number of those transform coefficients in the set of transform coefficients which are larger than a coefficient value threshold;
• and
• deriving the sign of the current transform coefficient according to a result of the determination.