Decoping apparatus for shape and pixel value signal

#This invention relates to an image encoding apparatus, an image decoding apparatus, an image encoding method, an image decoding method, an image encoding program recording medium and an image decoding program recording medium.

#The image encoding technology has a long history. There has been established excellent standard proposals such as ITU-T H.261, ITU-T H263, ISO MPEG1/2 and so on. Roughly speaking, the image encoding method has two approaches: an encoding method using the orthogonal transform and a prediction encoding method encoding the error of predicted values with the use of the prediction function.

#Although the encoding method using the orthogonal transform needs complicated calculation, when encoded signals of small bit numbers are obtained, it is possible to keep better picture quality than the prediction encoding method. The ordinary encoding method using orthogonal transform such as JPEG, MPEG and the like utilizes the DCT(Discrete Cosine Transform). Though it is known that DCT enables encoding by a small number of bits, it has own problems in that it needs high-precision multiplication, resulting in complicated calculation, and in that the reversible encoding is impossible. Accordingly, DCT calculation can not be used in the fields in which the reversibility is required.

#FIG. 1 is a block diagram showing the structure of an image encoding apparatus according to a 1st embodiment of this invention.

#FIGS. 2(a)-2(f) are drawings which explain the operation principles of an image encoding apparatus according to a 1st embodiment of this invention.

#FIG. 3 is a block diagram showing the structure of an image encoding apparatus according to a 2nd embodiment of this invention.

#Embodiment 1

#An image encoding apparatus according to a 1st embodiment of this invention performs efficient encoding in prediction encoding by selecting difference values having short code lengths within the given range.

#FIG. 1 is a block diagram showing the structure of the image encoding apparatus according to the 1st embodiment of this invention. In the figure, 1 indicates an input signal, which is input to the image encoding apparatus as a two-valued image signal. 2 indicates a change pixel detector which detects pixels changing pixel values in the input signal 1 and outputs the detected change pixels. 3 indicates a memory which temporarily stores already encoded and decoded image signals which are to be used as reference images. 4 indicates a change pixel predictor which predicts change pixels output by the change pixel detector 2 based on pixels changing pixel values of the reference image, and outputs predicted change pixels. As a prediction method used by the change pixel predictor 4, for example, there can be used the most typical method that predicts that a change pixel should be on a horizontal position the same as that on the upper-positioned scanning line, based on the strong vertical correlation of the two-dimensional image signal, and so on. 5 indicates a difference value calculator which calculates the difference value D between the change pixel detected by the change pixel detector 2 and the predictor 4. 6 indicates a value e which is a given value as the tolerance value of a rounding error and is input to a difference value rounder. 7 indicates the difference value rounder which modifies the difference value D within the range defined by the tolerance value e, and outputs a modified difference value D′. 8 indicates an encoder which encodes the difference value. 9 indicates the encoded signal which is output by the encoder 8. 11 indicates difference value adder which adds the modified difference value D′ and the predicted change pixel output by the change pixel predictor 4. 10 indicates a change pixel decoder which decodes the two-valued pixel using the result of the addition output by the difference value adder 11.