Entropy coding of transformation coefficients suitable for dependent scalar quantization

Abstract

To provide a video decoding method and a video decoder that are suitable for dependent quantization and can be effectively implemented for entropy coding in terms of coding efficiency.SOLUTION: A video decoder determines a first transform coefficient level of a first transform coefficient on the basis of a first significant coefficient flag, determines a reconstruction level set for the first transform coefficient level on the basis of a state variable, assigns a reconstruction level of the set reconstruction level to the first transform coefficient, and updates the state variable on the basis of a parity of the first transform coefficient level, selects a context on the basis of the updated state variable for decoding a second significant coefficient flag using context adaptive entropy decoding, and the second significant coefficient flag indicates whether a second transform coefficient level of a second transform coefficient that follows the first transform coefficient in scanning order is non-zero, and the second significant coefficient flag is decoded using the selected context.SELECTED DRAWING: None

Claims

[Claim 1] A video decoder for decoding a picture from a data stream, Based on a first significance level flag indicating whether the first transformation coefficient level is non-zero, the first transformation coefficient level of the first transformation coefficient is determined. Based on the state variables, determine the set of reconstruction levels for the first transformation coefficient level from among multiple sets of reconstruction levels. Based on the first conversion coefficient level, assign the reconstruction level of the reconstruction level set for the first conversion coefficient, The state variable is updated based on the parity of the first conversion coefficient level. A context is selected based on the updated state variable for decoding a second significance factor flag from the data stream using context-adaptive entropy decoding, the second significance factor flag indicating whether the second transformation factor level of the second transformation factor following the first transformation factor in the scan order is non-zero. The second significance factor flag is decoded using the selected context. A configured video decoder. [Claim 2] The video decoder according to claim 1, configured to determine the parity of the first conversion coefficient level by decoding a parity flag from the data stream. [Claim 3] The video decoder according to claim 2, configured to decode the parity flag using context-adaptive entropy decoding. [Claim 4] The video decoder according to claim 1, wherein the context is selected based on the position of the second conversion coefficient. [Claim 5] The video decoder according to claim 1, wherein the context is selected based on local activity around the second conversion coefficient. [Claim 6] The video decoder according to claim 1, wherein the state variable is any one of 0, 1, 2, or 3. [Claim 7] The video decoder according to claim 6, configured to select a first context when the state variable is 0 or 1, a second context when the state variable is 2, and a third context when the state variable is 3. [Claim 8] If the aforementioned state variable is 0: If the parity is 0, update the state variable to 0; if the parity is 1, update it to 2. When the aforementioned state variable is 1: If the parity is 0, update the state variable to 2; if the parity is 1, update it to 0. When the state variable is 2: If the parity is 0, update the state variable to 1; if the parity is 1, update it to 3. When the state variable is 3: If the parity is 0, update the state variable to 3; if the parity is 1, update it to 1. The video decoder according to claim 6, configured to update the state variable by doing so. [Claim 9] The video decoder according to claim 6, wherein the plurality of reconstruction level sets include two reconstruction level sets, and the video decoder is configured to select a first reconstruction level set when the state variable is 0 or 1, and to select a second reconstruction level set when the state variable is 3 or 4. [Claim 10] The video decoder according to claim 9, configured to decode a sign coefficient of 1 or -1 when the first conversion coefficient level is not zero, wherein the reconstruction level is assigned based on twice the first conversion coefficient level when the first reconstruction level set is selected, and based on twice the first conversion coefficient level minus the sign coefficient when the second reconstruction level set is selected. [Claim 11] A video decoding method for decoding a picture from a data stream, The first transformation coefficient level of the first transformation coefficient is determined based on a first significance coefficient flag that indicates whether the first transformation coefficient level is non-zero, Based on the state variables, determine the reconstruction level set for the first transformation coefficient level among multiple reconstruction level sets, Assigning a reconstruction level to the first conversion coefficient based on the first conversion coefficient level, Updating the state variable based on the parity of the first conversion coefficient level, A context is selected based on the updated state variable for decoding a second significance factor flag from the data stream using context-adaptive entropy decoding, wherein the second significance factor flag indicates whether the second transformation factor level of the second transformation factor following the first transformation factor in the scan order is non-zero, Decoding the second significance coefficient flag using the selected context, Video decoding methods, including... [Claim 12] The video decoding method according to claim 11, comprising determining the parity of the first conversion coefficient level by decoding a parity flag from the data stream. [Claim 13] The video decoding method according to claim 12, comprising decoding the parity flag using context-adaptive entropy decoding. [Claim 14] The video decoding method according to claim 11, wherein the context is selected based on the position of the second conversion coefficient. [Claim 15] The video decoding method according to claim 11, wherein the context is selected based on local activity around the second transformation coefficient. [Claim 16] The video decoding method according to claim 11, wherein the state variable is any one of 0, 1, 2, or 3. [Claim 17] The video decoding method according to claim 16, further comprising selecting a first context if the state variable is 0 or 1, selecting a second context if the state variable is 2, and selecting a third context if the state variable is 3. [Claim 18] If the aforementioned state variable is 0: If the parity is 0, update the state variable to 0; if the parity is 1, update it to 2. When the aforementioned state variable is 1: If the parity is 0, update the state variable to 2; if the parity is 1, update it to 0. When the state variable is 2: If the parity is 0, update the state variable to 1; if the parity is 1, update it to 3. When the state variable is 3: If the parity is 0, update the state variable to 3; if the parity is 1, update it to 1. The video decoding method according to claim 16, configured to update the state variable by doing so. [Claim 19] The video decoding method according to claim 16, wherein the plurality of reconstruction level sets include two reconstruction level sets, and the video decoding method includes selecting a first reconstruction level set when the state variable is 0 or 1, and selecting a second reconstruction level set when the state variable is 3 or 4. [Claim 20] The video decoding method according to claim 19, wherein when the first conversion coefficient level is not zero, a sign coefficient of 1 or -1 is decoded, and the reconstruction level is assigned based on twice the first conversion coefficient level when the first reconstruction level set is selected, and based on twice the result of subtracting the sign coefficient from the first conversion coefficient level when the second reconstruction level set is selected.

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