Recording medium, playback device, recording device, encoding method, and decoding method related to higher image quality

A recording method for recording a base video stream and an enhancement video stream, the recording method comprising:

• a first step of generating the base video stream by performing an irreversible conversion on an original image;
• and
• a second step of generating the enhancement video stream that includes a shift parameter and picture data, wherein
• a gradation bit sequence of each pixel constituting the picture data of the enhancement video stream represents a difference between a gradation bit sequence of each pixel constituting picture data of the original image and a gradation bit sequence of each pixel constituting picture data of the base video stream, and
• the shift parameter defines a shift operation that is performed by a playback device when the gradation bit sequence of the base video stream is added to the gradation bit sequence of the enhancement video stream.

A playback device for reading a base video stream and an enhancement video stream from a recording medium and playing back the base video stream and the enhancement video stream, wherein

• the base video stream is obtained by performing an irreversible conversion on an original image,
• the enhancement video stream includes a shift parameter and picture data,
• a gradation bit sequence of each pixel constituting the picture data of the enhancement video stream represents a difference between a gradation bit sequence of each pixel constituting picture data of the original image and a gradation bit sequence of each pixel constituting picture data of the base video stream, and
• the shift parameter defines a shift operation that is performed by a playback device when the gradation bit sequence of the base video stream is added to the gradation bit sequence of the enhancement video stream,
• the playback device comprising:
• a video decoder configured to obtain a gradation bit sequence for each pixel constituting picture data of the base video stream by decoding the base video stream;
• and
• a color depth extension unit configured to execute a color depth extension by performing a bit operation on the gradation bit sequence for each pixel constituting picture data of the base video stream by using the shift parameter and a gradation bit sequence of each pixel constituting the picture data of the enhancement video stream.

A recording device for recording a base video stream and an enhancement video stream onto a recording medium, the recording device comprising:

• a first encoding unit configured to obtain the base video stream by performing an irreversible conversion on an original image, the base video stream being composed of pixels each including a gradation bit sequence of a predetermined bit width;
• a decoding unit configured to obtain a non-compressed picture by decoding the base video stream, the non-compressed picture being composed of pixels each including a gradation bit sequence that is shorter than a gradation bit sequence of pixels of the original image in bit width;
• a calculating unit configured to calculate a difference between a gradation bit sequence of each pixel constituting the original image and a corresponding gradation bit sequence of the non-compressed picture of the base video stream;
• and
• a second encoding unit configured to generate the enhancement video stream that includes a shift parameter and picture data, wherein a gradation bit sequence of each pixel constituting the picture data of the enhancement video stream is the difference calculated by the calculating unit.

An encoding method comprising:

• a first encoding step of generating a base video stream by performing an encoding process on an original image;
• and
• a second encoding step of generating a picture-in-picture video stream in which each picture data is composed of picture-in-picture data, wherein
• the picture-in-picture data is picture data representing a part of a screen area for a picture in the base video stream, the part having been replaced with a child-screen area,
• an inter-picture predictive encoding process is performed in the second encoding step,
• pixel blocks located in the screen area excluding the child-screen area have been encoded by the inter-picture predictive encoding process by using only picture data of the base video stream as reference pictures.

A decoding method comprising:

• a first decoding step of obtaining non-compressed picture data by decoding a base video stream;
• and
• a second decoding step of obtaining picture-in-picture data by decoding a picture-in-picture video stream, wherein
• in the second decoding step, an inter-picture predictive motion compensation is performed on pixel blocks located in a screen area excluding a child-screen area in the picture-in-picture data, by using only picture data included in the base video stream as reference pictures.