Method and device for encoding or decoding and image

A method of decoding coefficients of a video signal, the video signal having at least a first signal component, corresponding to a first color component, and a second signal component, associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks comprising at least one coefficient, and each block having one or more decodable units, and the decoding of at least one decodable unit of the second signal component being switchable between first and second modes, the decoding in the first mode including an inverse transforming step for transforming coefficients into decodable units and the decoding in the second mode excluding the inverse transforming step, the method comprising:

• excluding, for at least one decodable unit of the second signal component, the use of said second mode for the decoding of the decodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component decodable unit concerned is a sub-divided block having at least two decodable units and the second mode is not used for decoding any of the decodable units of the sub-divided first-signal-component block;
• and
• when the condition is not satisfied, enabling a choice of which of the first and second decoding modes to use for the decoding of the second-signal-component decodable unit concerned.

An encoder for encoding a video signal having at least a first signal component, corresponding to a first color component, and a second signal component associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks, and each said block having one or more encodable units, and the encoding of at least one encodable unit of said second signal component being switchable between first and second modes, the encoding in the first mode including transforming an encodable unit into coefficients, and the encoding in the second mode excluding said transforming of an encodable unit into coefficients, the encoder comprising:

• an excluding unit which excludes means for excluding, for at least one said encodable unit of said second signal component, use of said second mode for the encoding of the second-signal-component encodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component encodable unit concerned is a sub-divided block having at least two encodable units, and the second mode is not used for encoding any of the encodable units of the sub-divided first-signal-component block;
• and
• an enabling unit which enables a choice of which of the first and second encoding modes to use for the encoding of the second-signal-component encodable unit concerned when the condition is not satisfied.

A decoder for decoding coefficients of a video signal, the video signal having at least a first signal component, corresponding to a first color component, and a second signal component, associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks comprising at least one coefficient, and each block having one or more decodable units, and the decoder being configured so that the decoding of at least one decodable unit of the second signal component is switchable between first and second modes, the decoding in the first mode including inverse transforming, and the decoding in the second mode excluding said inverse transforming, the decoder comprising:

• an excluding unit which excludes, means for excluding for at least one said decodable unit of said second signal component, use of said second mode for the encoding of the second-signal-component decodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component decodable unit concerned is a sub-divided block having at least two decodable units and the second mode is not used for decoding any of the decodable units of the sub-divided first-signal-component block;
• an enabling unit which enables a choice of which of the first and second decoding modes to use for the decoding of the second-signal-component decodable unit concerned when the condition is not satisfied;
• and
• a generating unit which generates a flag having a predetermined value indicating that an encoder did not use said second mode, in the event that the condition is satisfied.

A non-transitory computer-readable storage medium storing a program which, when executed by a computer or processor, causes the computer or processor to carry out a method of encoding a video signal, the video signal having at least a first signal component corresponding to a first color component, and a second signal component, associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks, and each said block having one or more encodable units, and the encoding of at least one encodable unit of said second signal component being switchable between first and second modes, the encoding in the first mode including a transforming step for transforming an encodable unit into coefficients, and the encoding in the second mode excluding the transforming step, the program comprising:

• a code portion which excludes, for at least one said encodable unit of said second signal component, use of said second mode for the encoding of the second-signal-component encodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component encodable unit concerned is a sub-divided block having at least two encodable units, and the second mode is not used for encoding any of the encodable units of the sub-divided first-signal-component block;
• and
• a code portion which enables a choice of which of the first and second encoding modes to use for the encoding of the second-signal-component encodable unit concerned when the condition is not satisfied.

A non-transitory computer-readable storage medium storing a program which, when executed by computer or processor, causes the computer or processor to carry out a method of decoding coefficients of a video signal, the video signal having at least a first signal component, corresponding to a first color component, and a second signal component, associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks comprising at least one coefficient, and each block having one or more decodable units, and the decoding of at least one decodable unit of the second signal component being switchable between first and second modes, the decoding in the first mode including an inverse transforming step for transforming step for transforming coefficients into decodable units and the decoding in the second mode excluding the inverse transforming step, the program comprising:

• a code portion which excludes, for at least one decodable unit of the second signal component, the use of said second mode for the decoding of the decodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component decodable unit concerned is a sub-divided block having at least two decodable units and the second mode is not used for decoding any of the decodable units of the sub-divided first-signal-component block;
• and
• a code portion which enables a choice of which of the first and second decoding modes to use for the decoding of the second-signal-component decodable unit concerned when the condition is not satisfied.

A method of encoding a video signal having at least a first signal component corresponding to a first color component, and a second signal component, associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks, and each said block having one or more encodable units, and the encoding of at least one encodable unit of said second signal component being switchable between first and second modes, the encoding in the first mode including a transforming step for transforming an encodable unit into coefficients, and the encoding in the second mode excluding the transforming step, the method comprising:

• excluding, for at least one said encodable unit of said second signal component, use of said second mode for the encoding of the second-signal-component encodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component encodable unit concerned comprises only one encodable unit;
• and
• when the condition is not satisfied, enabling a choice of which of the first and second encoding modes to use for the encoding of the second-signal-component encodable unit concerned.

A method of decoding coefficients of a video signal, the video signal having at least a first signal component, corresponding to a first color component, and a second signal component, associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks comprising at least one coefficient, and each block having one or more decodable units, and the decoding of at least one decodable unit of the second signal component being switchable between first and second modes, the decoding in the first mode including an inverse transforming step for transforming coefficients into decodable units and the decoding in the second mode excluding the inverse transforming step, the method comprising:

• excluding, for at least one decodable unit of the second signal component, the use of said second mode for the decoding of the decodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component decodable unit concerned comprises only one decodable unit;
• and
• when the condition is not satisfied, enabling a choice of which of the first and second decoding modes to use for the encoding of the second-signal-component decodable unit concerned.

An encoder for encoding a video signal having at least a first signal component, corresponding to a first color component, and a second signal component associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks, and each said block having one or more encodable units, and the encoding of at least one encodable unit of said second signal component being switchable between first and second modes, the encoding in the first mode including transforming an encodable unit into coefficients, and the encoding in the second mode excluding said transforming of an encodable unit into coefficients the encoder comprising:

• an excluding unit which excludes, for at least one said encodable unit of said second signal component, use of said second mode for the encoding of the second-signal-component encodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component encodable unit concerned comprises only one encodable unit;
• and
• an enabling unit which enables a choice of which of the first and second encoding modes to use for the encoding of the second-signal-component encodable unit concerned when the condition is not satisfied.

A decoder for decoding coefficients of a video signal, the video signal having at least a first signal component, corresponding to a first color component, and a second signal component, associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks comprising at least one coefficient, and each block having one or more decodable units, and the decoder being configured so that the decoding of at least one decodable unit of the second signal component is switchable between first and second modes, the decoding in the first mode including inverse transforming, and the decoding in the second mode excluding said inverse transforming, the decoder comprising:

• an excluding unit which excludes, for at least one said decodable unit of said second signal component, use of said second mode for the decoding of the second-signal-component decodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component decodable unit concerned comprises only one decodable unit;
• an enabling unit which enables a choice of which of the first and second decoding modes to use for the decoding of the second-signal-component decodable unit concerned when the condition is not satisfied;
• and
• a generating unit which generates a flag having a predetermined value indicating that an encoder did not use said second mode, in the event that the condition is satisfied.

A non-transitory computer-readable storage medium storing a program which, when executed by a computer or processor, causes the computer or processor to carry out a method of encoding a video signal, the video signal having at least a first signal component corresponding to a first color component, and a second signal component, associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks, and each said block having one or more encodable units, and the encoding of at least one encodable unit of said second signal component being switchable between first and second modes, the encoding in the first mode including a transforming step for transforming an encodable unit into coefficients, and the encoding in the second mode excluding the transforming step, the program comprising:

• a code portion which excludes, for at least one said encodable unit of said second signal component, use of said second mode for the encoding of the second-signal-component encodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component encodable unit concerned comprises only one encodable unit;
• and
• a code portion which enables a choice of which of the first and second encoding modes to use for the encoding of the second-signal-component encodable unit concerned when the condition is not satisfied.

A non-transitory computer-readable storage medium storing a program which, when executed by computer or processor, causes the computer or processor to carry out a method of decoding coefficients of a video signal, the video signal having at least a first signal component, corresponding to a first color component, and a second signal component, associated with the first signal component and corresponding to a second color component, each said signal component being divided into blocks comprising at least one coefficient, and each block having one or more decodable units, and the decoding of at least one decodable unit of the second signal component being switchable between first and second modes, the decoding in the first mode including an inverse transforming step for transforming coefficients into decodable units and the decoding in the second mode excluding the inverse transforming step, the program comprising:

• a code portion which excludes, for at least one decodable unit of the second signal component, the use of said second mode for the decoding of the decodable unit concerned when the following condition is satisfied:
• the first-signal-component block corresponding to the second-signal-component decodable unit concerned comprises only one decodable unit;
• and
• a code portion which enables a choice of which of the first and second decoding modes to use for the decoding of the second-signal-component decodable unit concerned when the condition is not satisfied.