Method and apparatus for encoding/decoding image using transform skip flag

A method of decoding, based on loss coding, a video signal having a current block to be decoded with a decoding apparatus, comprising:

• obtaining, from the video signal, residual coefficients relating to the current block, a first transform skip flag relating to luma components of the current block and a second transform skip flag relating to chroma components of the current block,
• wherein the residual coefficients include first residual coefficients relating to the luma components of the current block and second residual coefficients relating to the chroma components of the current block;
• performing an inverse-quantization on the first residual coefficients and the second residual coefficients of the current block;
• obtaining residual samples of the current block by selectively performing an inverse-transform for first inverse-quantized residual coefficients resulting from the inverse quantization of the first residual coefficients and second inverse-quantized residual coefficients resulting from the inverse-quantization of the second residual coefficients,
• wherein the first transform skip flag specifies whether the inverse-transform is performed or skipped on the first inverse-quantized residual coefficients resulting from the inverse-quantization of the first residual coefficients, and the second transform skip flag specifies whether the inverse-transform is performed or skipped on the second inverse-quantized residual coefficients resulting from the inverse-quantization of the second residual coefficients,
• wherein determination of skipping the inverse-transform on the first inverse-quantized residual coefficients is independent with determination of skipping the inverse-transform on the second inverse-quantized residual coefficients, and
• wherein when the first transform skip flag specifies that the inverse-transform is skipped on the first inverse-quantized residual coefficients, the residual samples of the luma components of the current block is obtained by scaling the first inverse-quantized residual coefficients, and when the second transform skip flag specifies that the inverse-transform is skipped on the second inverse-quantized residual coefficients, the residual samples of the chroma components of the current block is obtained by scaling the second inverse-quantized residual coefficients;
• performing an intra prediction or an inter prediction for the current block;
• and
• reconstructing the current block by using the residual samples and prediction samples obtained by performing the intra prediction or the inter prediction.