Image encoding/image decoding method and image encoding/image decoding apparatus
An image coding method includes dividing an input picture into a plurality of pixel block signals, performing intra prediction for extrapolating or interpolating a prediction pixel using reference pixels changed in number according to a distance between the prediction pixel and a reference pixel in plural prediction modes each representing a prediction direction, generating a predictive image signal by extrapolating or interpolating the prediction pixel, calculating a prediction error signal from the pixel block signal and the predictive image signal, selecting one prediction mode of the plural prediction modes using the prediction error signal, and performing entropy-coding using the prediction error signal based on the selected prediction mode.
1. An image decoding method comprising:
decoding an input image signal to generate a decoded image signal including prediction mode information;
changing the number of reference pixels for use in prediction and a procedure for prediction pixel generation according to a selected prediction mode based on the prediction mode information;
generating a predictive image signal by extrapolating or interpolating using a distance between an reference pixel and a prediction pixel;
generating a prediction error signal based on the decoded image signal; and
generating a reconstructed image by adding the predictive image signal and the prediction error signal.
2. The method according to claim 1 further including changing in a specific pixel block size a size of the prediction pixel block corresponding to the prediction mode every prediction mode.
3. The method according to claim 1 further including predicting a prediction mode and switching between decoding and non-decoding of predicted prediction mode information in a specific pixel block size.
4. The method according to claim 1 , wherein generating the predictive image signal includes changing a weighted table of a filter for use in prediction according to the distance between the reference pixel and the prediction pixel.
5. The method according to claim 1 , wherein generating the predictive image signal includes dequantizing transform coefficient of the decoded image signal, and inverse-transforming the dequantized transform coefficient to generate the prediction error signal.
6. The method according to claim 1 , wherein generating the predictive image signal includes switching adaptively between use and unuse of the predicted prediction image signal.
7. The method according to claim 1 , wherein generating the predictive image signal includes switching adaptively between use and unuse of the decoded reference image.
8. The method according to claim 1 , wherein generating the predictive image signal includes switching between execution and inexecution of intra prediction.
9. The method according to claim 1 , further including switching between the prediction modes according to a value of a quantization parameter of the image block signal.
10. The method according to claim 1 , further including switching between the prediction modes according to resolution of the input image signal.
11. The method according to claim 1 , wherein the generating the prediction signal includes changing a procedure for prediction pixel generation according to a prediction direction prescribed by the prediction mode when performing extrapolation or interpolation in units of pixel, and saving temporally the encoded reference pixel and the extrapolated or interpolated prediction pixel in a memory to use for next prediction.
12. An image decoding apparatus comprising:
a decoder to decode an input image signal to generate a decoded image signal including prediction mode information;
a generator to generate a predictive image signal by changing the number of reference pixels for use in prediction and a procedure for prediction pixel generation according to a selected prediction mode based on the prediction mode information of the decoded image signal and a distance between an encoded reference pixel and a prediction pixel, and performing intra prediction for extrapolating or interpolating the decoded image signal in units of pixel;
a generator to generate a prediction error signal based on the decoded image signal; and
a generator generating a reconstructed image by adding the predictive image signal and the prediction error signal.
13. A computer-readable medium storing a program for decoding an encoded image, the program comprising:
means for instructing a computer to decode an input image signal to generate a decoded image signal including prediction mode information;
means for instructing the computer to change the number of reference pixels for use in prediction and a procedure for prediction pixel generation according to a selected prediction mode based on the prediction mode information of the decoded image signal and a distance between an reference pixel and a prediction pixel;
means for instructing the computer to generate a predictive image signal by intra-picture prediction for extrapolating or interpolating the decoded image signal in units of pixel;
means for instructing the computer to generate a prediction error signal based on the decoded image signal; and
means for instructing the computer to generate a reconstructed image by adding the predictive image signal and the prediction error signal.