Image encoding method and device, image decoding method and device, and imaging device

An image encoding method for obtaining, from a pixel data string containing m-bit pixel values of a plurality of pixels in a pixel array where the pixels are arrayed, a pixel data string containing n-bit quantized representative values into which difference values between the pixel values are encoded, the method comprising:

• calculating a difference value between a pixel value of a first pixel and a pixel value of a second pixel adjacent to the first pixel;
• representing the difference value by a k-bit quantized representative value according to the difference value;
• and
• converting the k-bit quantized representative value of the difference value into one of the n-bit quantized representative values to encode the k-bit quantized representative value, wherein
• when the pixel value of the second pixel is a specific pixel value, as the difference value, the value is converted into a specific quantized representative value.

An image encoding device for obtaining, from a pixel data string containing m-bit pixel values of a plurality of pixels in a pixel array where the pixels are arrayed, a pixel data string containing n-bit quantized representative values into which difference values between the pixel values are encoded, the device comprising:

• a difference value calculating unit that calculates a difference value between a pixel value of a first pixel and a pixel value of a second pixel adjacent to the first pixel;
• an intermediate quantizing unit that represents the difference value by a k-bit quantized representative value according to the difference value;
• a specific pixel value determining unit that determines whether the pixel value of the second pixel is a specific pixel value;
• and
• an encoding unit that performs encoding by converting the k-bit quantized representative value of the difference value into one of the n-bit quantized representative values when the pixel value of the second pixel is the specific pixel value, and by converting the k-bit quantized representative value of the difference value into one of quantized representative values other than the specific quantized representative value of n bits when the pixel value of the second pixel is other than the specific pixel value.

An image decoding method for obtaining, from a pixel data string containing an n-bit quantized representative value into which a difference value between pixels is encoded, a pixel data string containing a decoded m-bit pixel value, the method comprising:

• depacking a pixel data string that has been encoded;
• obtaining a first coded value as a pixel value of a first pixel;
• obtaining a second coded value as an encoded quantized representative value of a difference value between the pixel value of the first pixel and a pixel value of a second pixel;
• determining whether the second coded value is a specific quantized representative value;
• obtaining the difference value between the pixel value of the first pixel and the pixel value of the second pixel by decoding the second coded value;
• and
• obtaining the pixel value of the second pixel by adding the difference value that has been decoded to the pixel value of the first pixel that has been decoded, wherein
• when the second coded value is the specific quantized representative value, the pixel value of the second pixel is decoded by allocating a specific pixel value.

An image decoding device for obtaining, from a pixel data string containing an n-bit quantized representative value into which a difference value between pixels is encoded, a pixel data string containing a decoded m-bit pixel value, the device comprising:

• a depacking unit that depacks a pixel data string that has been encoded;
• a coded value extracting unit that obtains a first coded value as a pixel value of a first pixel, and that obtains a second coded value as an encoded quantized representative value of a difference value between the pixel value of the first pixel and a pixel value of a second pixel;
• a specific pixel value determining unit that determines whether the second coded value is a specific quantized representative value;
• and
• a decoding unit that decodes by allocating a specific pixel value as the pixel value of the second pixel when the second coded value is the specific quantized representative value;
• and obtains the difference value by decoding the second coded value, and that obtains the pixel value of the second pixel by adding the difference value to the pixel value of the first pixel that has been decoded, when the second coded value is not the specific quantized representative value.