Method and device for processing video signal by using adaptive color space transform

A device for encoding a video signal, the device comprising a processor,

• wherein the processor is configured to:
• obtain information related to a minimum allowed quantization parameter for a transform skip mode based on whether a transform skip flag is present in a transform unit syntax or whether a palette mode is enabled,
• wherein the transform skip flag indicates whether the transform skip mode is applied to a transform block included in a current block,
• wherein when the transform skip mode is applied to the transform block, no transform is applied to the transform block,
• obtain the minimum allowed quantization parameter based on the information related to the minimum allowed quantization parameter,
• obtain a first modified quantization parameter by adding a quantization parameter and a quantization parameter offset,
• wherein the quantization parameter offset is determined based on whether a color space conversion is applied to the current block,
• obtain a second modified quantization parameter by clipping the first modified quantization parameter,
• wherein when the transform skip flag indicates that the transform skip mode is not applied to the transform block and the first modified quantization parameter is less than 0, the second modified quantization parameter is obtained by clipping the first modified quantization parameter to 0,
• wherein when the transform skip flag indicates that the transform skip mode is applied to the transform block and the first modified quantization parameter is less than the minimum allowed quantization parameter, the second modified quantization parameter is obtained by clipping the first modified quantization parameter to the minimum allowed quantization parameter,
• reconstruct the current block based on the second modified quantization parameter, and
• obtain a bitstream including information for reconstructing the current block.

A non-transitory computer-readable medium storing a bitstream, the bitstream being decoded by a decoding method, the decoding method comprising:

• obtaining information related to a minimum allowed quantization parameter for a transform skip mode based on whether a transform skip flag is present in a transform unit syntax or whether a palette mode is enabled,
• wherein the transform skip flag indicates whether the transform skip mode is applied to a transform block included in a current block;
• wherein when the transform skip mode is applied to the transform block, no transform is applied to the transform block;
• obtaining the minimum allowed quantization parameter based on the information related to the minimum allowed quantization parameter;
• obtaining a first modified quantization parameter by adding a quantization parameter and a quantization parameter offset,
• wherein the quantization parameter offset is determined based on whether a color space conversion is applied to the current block;
• obtaining a second modified quantization parameter by clipping the first modified quantization parameter,
• wherein when the transform skip flag indicates that the transform skip mode is not applied to the transform block and the first modified quantization parameter is less than 0, the second modified quantization parameter is obtained by clipping the first modified quantization parameter to 0,
• wherein when the transform skip flag indicates that the transform skip mode is applied to the transform block and the first modified quantization parameter is less than the minimum allowed quantization parameter, the second modified quantization parameter is obtained by clipping the first modified quantization parameter to the minimum allowed quantization parameter;
• and
• reconstructing the current block based on the second modified quantization parameter.

A method for decoding a video signal, comprising:

• obtaining information related to a minimum allowed quantization parameter for a transform skip mode based on whether a transform skip flag is present in a transform unit syntax or whether a palette mode is enabled,
• wherein the transform skip flag indicates whether the transform skip mode is applied to a transform block included in a current block;
• wherein when the transform skip mode is applied to the transform block, no transform is applied to the transform block;
• obtaining the minimum allowed quantization parameter based on the information related to the minimum allowed quantization parameter;
• obtaining a first modified quantization parameter by adding a quantization parameter and a quantization parameter offset,
• wherein the quantization parameter offset is determined based on whether a color space conversion is applied to the current block;
• obtaining a second modified quantization parameter by clipping the first modified quantization parameter,
• wherein when the transform skip flag indicates that the transform skip mode is not applied to the transform block and the first modified quantization parameter is less than 0, the second modified quantization parameter is obtained by clipping the first modified quantization parameter to 0,
• wherein when the transform skip flag indicates that the transform skip mode is applied to the transform block and the first modified quantization parameter is less than the minimum allowed quantization parameter, the second modified quantization parameter is obtained by clipping the first modified quantization parameter to the minimum allowed quantization parameter;
• reconstructing the current block based on the second modified quantization parameter.