Encoding apparatus and method and storage medium

An encoding method for encoding each of target pixels composing one screen, comprising the steps of:

• a prediction value generating step of generating a prediction value by predicting a target pixel value representing a target pixel on the basis of pixels around the target pixel;
• a difference generating step of generating a difference between the prediction value generated in said prediction value generating step and the target pixel value;
• a quantization step of generating a quantized value by quantizing the difference generated in said difference generating step;
• an entropy encoding step of generating encoded data by entropy-encoding the quantized value generated in said quantization step;
• and
• a quantization control step of selecting one of k quantization methods, which is to be used in said quantization step for every part image composing the one screen,
• wherein each part image consists of a plurality of pixels, and each of the k quantization methods is a quantization method which makes an error between the difference generated in said difference generating step and a quantized value obtained by quantizing the difference in said quantization step fall within a range of −Nm to +Nm, wherein m=1 to k.

A storage medium storing computer-readable program code for performing a method of encoding each of target pixels composing one screen, the method comprising the steps of:

• a prediction value generating step of generating a prediction value by predicting a target pixel value representing a target pixel on the basis of pixels around the target pixel;
• a difference generating step of generating a difference between the prediction value generated in said prediction value generating step and the target pixel value;
• a quantization step of generating a quantized value by quantizing the difference generated in said difference generating step;
• an entropy encoding step of generating encoded data by entropy-encoding the quantized value generated in said quantization step;
• and
• a quantization control step of selecting one of k quantization methods, which is to be used in said quantization step for every part image composing the one screen,
• wherein each part image consists of a plurality of pixels, and each of the k quantization methods is a quantization method which makes an error between the difference generated in said difference generating step and a quantized value obtained by quantizing the difference in said quantization step fall within a range of −Nm to +Nm, wherein m=1 to k.