Apparatus for prediction coding or decoding image signal and method therefor

A method for predicting an image signal in a method for predictive coding or predictive decoding an image signal using a prediction memory which comprises a horizontal direction memory unit which has storage areas capable of storing horizontal DCT components of a slice forming a scene, a vertical direction memory unit which has storage areas capable of storing a vertical DCT component, and an upper-left memory unit storage areas capable of storing a DC component of a block immediately above and to the left of a current block for which prediction is performed, the method for prediction an image signal comprises:

• (a) determining whether or not the packet to which the current macro block belongs is different from the packet of a macro block to the left of the current macro block, the macro block immediately above and to the left of the current block, or a macro block immediately above the current macro block, using a current packet change signal indicating whether or not the packet to which the current macro block belongs changed;
• (b) if the packet to which the current macro block belongs is the same as the packet of the macro block to the left of the current macro block, the macro block immediately above and to the left of the current block, or the macro block immediately above the current macro block, determining the direction of prediction, using the DC component of the block to the left of the current block stored in the vertical direction memory unit, the DC component of the block immediately above the current block stored in the horizontal direction memory unit, and the DC component of the block immediately above and to the left of the current block;
• (c) if the prediction direction is a first direction, outputting a reference prediction value by using a value stored in the vertical direction memory unit and if the prediction direction is a second direction, outputting a reference prediction value by using a value stored in the horizontal direction memory unit;
• (d) if the packet to which the current macro block belongs is different from the packet of the macro block to the left of the current macro block, the macro block immediately above and to the left of the current block, or the macro block immediately above the current macro block, outputting a predetermined reference value;
• (e) performing prediction calculation by using the reference prediction value of step (c) or the predetermined reference value of step (c) with the DCT component of the current block;
• and
• (f) storing the DCT component of the current block in the prediction memory.

A computer readable medium having embodied thereon a computer program for implementing a method for predicting an image signal in a method for predictive coding or predictive decoding an image signal using a prediction memory which comprises a horizontal direction memory unit which has storage areas capable of storing horizontal DCT components of a slice forming a scene, a vertical direction memory unit which has storage areas capable of storing vertical DCT components, and an upper-left memory unit storage areas capable of storing a DC component of a upper left-hand block of a current block for which prediction is performed, the method for prediction an image signal comprises:

• (a) determining whether or not the packet to which the current macro block belongs is different from the packet of a left-hand macro block of the current macro block, the upper left-hand macro block of the current macro block, or an upper macro block of the current macro block, using a current packet change signal indicating whether or not the packet to which the current macro block belongs changed;
• (b) if the packet to which the current macro block belongs is the same as the packet of the left-hand macro block of the current macro block, the upper left-hand macro block of the current macro block, or the upper macro block of the current macro block, determining the direction of prediction, using the DC component of the left-hand block of the current block stored in the vertical direction memory unit, the DC component of the upper block of the current block stored in the horizontal direction memory unit, and the DC component of the upper left-hand block of the current block;
• (c) if the prediction direction is a first direction, outputting a reference prediction value by using a value stored in the vertical direction memory unit and if the prediction direction is a second direction, outputting a reference prediction value by using a value stored in the horizontal direction memory unit;
• (d) if the packet to which the current macro block belongs is different from the packet of the left-hand macro block of the current macro block, the upper left-hand macro block of the current macro block, or the upper macro block of the current macro block, outputting a predetermined reference value;
• (e) performing prediction calculation by using the reference prediction value of step (c) or the predetermined reference value of step (c) with the DCT component of the current block;
• and
• (f) storing the DCT component of the current block in the prediction memory.