Entropy decoding method using context information

1. An entropy decoding method based on a context adaptive binary arithmetic coding, the method comprising:

deriving, by a decoding apparatus, context information on at least one bin among bins of a bin string for an intra_chroma_pred_mode syntax element;

decoding, by the decoding apparatus, the bins of the bin string, wherein a regular decoding is performed for the first bin among the bin string based on the context information and a bypass decoding is performed for the remaining bins among the bin string;

deriving, by the decoding apparatus, a value of the intra_chroma_pred_mode syntax element based on the decoded bins; and

generating, by the decoding apparatus, prediction samples based on the value of the intra_chroma_pred_mode syntax elements.

2. The method of claim 1 , wherein the step of decoding bins comprises applying the bypass decoding on the remaining bins of the bin string for the intra_chroma_pred_mode syntax element and applying contexts which are independent of each other to other bins of the bin string for the intra_chroma_pred_mode syntax element.

3. The method of claim 1 , wherein in the step of the decoding bins, independent context is applied to the first bin which is decoded based on the context information, and

wherein the independent context is a context which is updated independently from other context.

4. The method of claim 1 , wherein the step of decoding bins comprises:

determining whether the bypass decoding is performed on the remaining bins of the bin string for the intra_chroma_pred_mode syntax element; and

decoding the remaining bins based on the context information when it is determined that the bypass decoding is not performed on the remaining bins.

5. The method of claim 1 , wherein the step of decoding bins comprises decoding the first bin of the bin string for the intra_chroma_pred_mode syntax element based on a context index assigned to the first bin from a context index table which assigns a context index to a bin corresponding to the intra_chroma_pred_mode syntax element.

6. The method of the claim 1 , wherein, in the step of decoding bins, the first bin is decoded using a context index table,

wherein the context index table allocates an offset corresponding to a picture type for a picture to be decoded and context index for the first bin of the bin string for the intra_chroma_pred_mode syntax element, and

wherein the first bin of the bin string for the syntax element is decoded based on a context indicated by the context index and the offset.

7. The method of claim 1 , wherein a binary code of a bin is decoded as it is not using a context when the bypass decoding is performed.

8. The method of claim 1 , wherein, in the step of deriving context information, a bin index of 0 is allocated to the first bin, and the bypass decoding is performed on the remaining bins.

9. The method of claim 1 , wherein the intra_chroma_pred_mode syntax element specifies an intra prediction mode for a chroma sample.

10. The method of claim 1 , wherein the step of decoding bins comprises:

performing the regular decoding on the first bin of the bin string for the intra_chroma_pred_mode syntax element based on the context information; and

performing the bypass decoding on a second bin through the last bin of the bin string for the intra_chroma_pred_mode syntax element.

11. The method of claim 10 , wherein the context information is specified by a sum of context index of the first bin, and

wherein the context index offset has a value of 0 when a current slice is an I slice, a value of 1 when the current slice is a P slice, and a value of 2 when the current slice is a B slice.