Method and apparatus for selecting a coding mode used for encoding/decoding a residual block

A method for decoding a picture comprising:

• decoding a residual block by:
• obtaining a first coding mode defining a 2D separable transform when coding the residual blocks according to a coding mode defining a 2D separable transform is enabled;
• obtaining a second coding mode defining a non-separable 2D transform when coding the residual blocks according to a coding mode defining a non-separable 2D transform is enabled;
• and
• decoding the residual block according to either said first coding mode or said second coding mode or both,
• wherein the method is characterized in that enabling or disabling the coding of the residual block according to said second coding mode depends on said first coding mode.

A device for encoding a residual block comprising means for:

• obtaining a first coding mode defining a separable 2D transform when coding the residual blocks according to a coding mode using a separable 2D transform is enabled;
• obtaining a second coding mode using a non-separable 2D transform when coding the residual blocks according to a coding mode defining a second 2D transform is enabled;
• and
• encoding the residual block according to either said first coding mode or said second coding mode or both,
• wherein the device is characterized in that enabling or disabling the coding of the residual block according to said second coding mode depends on said first coding mode.

A device for decoding a picture comprising:

• a device for decoding a residual block comprising means for:
• obtaining a first coding mode defining a separable 2D transform when coding the residual blocks according to a coding mode using a separable 2D transform is enabled;
• obtaining a second coding mode using a non-separable 2D transform when coding the residual blocks according to a coding mode defining a second 2D transform is enabled;
• and
• decoding the residual block according to either the first coding mode or said second coding mode or both,
• wherein the device is characterized in that enabling or disabling the coding of the residual block according to the second coding mode depends on the first coding mode.

A non-transitory storage medium carrying instructions of program code operative, when said program is executed on a computing device, to cause the computing device to:

• obtain a first coding mode defining a 2D separable transform when coding the residual blocks according to a coding mode defining a 2D separable transform is enabled;
• obtain a second coding mode defining a non-separable 2D transform when coding the residual blocks according to a coding mode defining a non-separable 2D transform is enabled;
• and
• decode the residual block according to either the first coding mode or the second coding mode or both,
• wherein enabling or disabling the coding of the residual block according to the second coding mode depends on said first coding mode.