Method, device and system for encoding and decoding image
Disclosed are methods, apparatuses, and systems for encoding and decoding an image. The present invention provides an intra prediction unit receives an input image, removes high frequency ingredients by low pass filtering an encoded luma pixel value in the input image during intra prediction, and generates a prediction block by predicting a chroma pixel value by using a low pass filter (LPF) LM chroma mode for applying an LM chroma mode, which is an extended chroma mode technique for generating a prediction block by predicting the chroma pixel value by applying a correlation between color planes to the luma pixel value having removed therefrom the high frequency ingredients.
1. An image encoding method employed by an image encoding apparatus comprising a processor, the method comprising:
selecting one of an intra prediction mode and an inter prediction mode as a prediction mode of a current block; and
predicting, in response to the intra prediction mode being selected as the prediction mode of the current block, a chroma pixel of the current block based on one of a plurality of LMmode candidates of a LMmode, the LMmode representing that chroma pixels are predicted by luma pixels,
wherein a flag specifying whether the LMmode is applied to the current block is encoded into a bitstream,
wherein, in response to the flag specifying that the LMmode is applied to the current block, index information specifying the one of the plurality of LMmode candidates selected for the current block is additionally encoded into the bitstream, and the plurality of LMmode candidates comprises a first LMmode and a second LMmode,
wherein predicting the chroma pixel of the current block comprises:
obtaining a first filtered luma value to predict the chroma pixel;
obtaining a weight and an offset based on a linear relationship between luma pixels and chroma pixels; and
predicting the chroma pixel based on the first filtered luma value, the weight and the offset,
wherein, under the first LMmode, the weight and the offset are obtained based on a second filtered luma value, while, under the second LMmode, the weight and the offset are obtained in absence of the second filtered luma value,
wherein a horizontal neighboring luma pixel adjacent to a co-located luma pixel is relied on to derive the first filtered luma value and the co-located luma pixel having a position corresponding to the chroma pixel,
wherein the first filtered luma value is obtained based on a weighted sum operation using the co-located luma pixel and the horizontal neighboring luma pixel, and
wherein the chroma pixel is predicted by an equation C pred [x, y]=αG recon lpf [x, y]+β (wherein, G recon lpf [x, y] denotes the first filtered luma value, α denotes the weight, and β denotes the offset), and wherein the second filtered luma value is obtained based on a neighboring luma pixel.
2. The method of claim 1 , wherein the horizontal neighboring luma pixel comprises at least one of a left neighboring luma pixel and a right neighboring luma pixel.
3. An image decoding method employed by an image decoding apparatus comprising a processor, the method comprising:
determining a prediction mode of a current block as one of an intra prediction mode and an inter prediction mode; and
determining, in response to the prediction mode of the current block being the intra prediction mode, whether a LMmode that represents that a chroma pixel is predicted by a luma pixel is applied to the current block based on a flag parsed from a bitstream;
selecting one of a plurality of LMmode candidates of the LMmode; and
predicting the chroma pixel of the current block according to the selected LMmode candidate,
wherein when it is determined that the LMmode is applied to the current block, index information is additionally parsed from the bitstream, the index information specifies the one of the plurality of LMmode candidates applied to the current block, and the plurality of LMmode candidates comprises a first LMmode and a second LMmode,
wherein predicting the chroma pixel of the current block comprises:
obtaining a first filtered luma value to predict the chroma pixel;
obtaining a weight and an offset based on a linear relationship between luma pixels and chroma pixels; and
predicting the chroma pixel based on the first filtered luma value, the weight and the offset,
wherein, under the first LMmode, the weight and the offset are obtained based on a second filtered luma value, while, under the second LMmode, the weight and the offset are obtained in absence of the second filtered luma value,
wherein a horizontal neighboring luma pixel adjacent to a co-located luma pixel is relied on to derive the first filtered luma value, and the co-located luma pixel has a position corresponding to the chroma pixel,
wherein the first filtered luma value is obtained based on a weighted sum operation using the co-located luma pixel and the horizontal neighboring luma pixel; and
wherein the chroma pixel is predicted by an equation C pred [x, y]=αG recon lpf [x, y]+β (wherein, G recon lpf [x, y] denotes the first filtered luma value, α denotes the weight, and β denotes the offset), and wherein the second filtered luma value is obtained based on a neighboring luma pixel.
4. The method of claim 3 , wherein the horizontal neighboring luma pixel comprises at least one of a left neighboring luma pixel and a right neighboring luma pixel.
5. A method of transmitting a bitstream generated by an encoding method, the encoding method comprising:
selecting one of an intra prediction mode and an inter prediction mode as a prediction mode of a current block; and
predicting, in response to the intra prediction mode being selected as the prediction mode of the current block, a chroma pixel of the current block based on one of a plurality of LMmode candidates of a LMmode, the LMmode representing that chroma pixels are predicted by luma pixels,
wherein a flag specifying whether the LMmode is applied to the current block is encoded into the bitstream,
wherein, in response to the flag specifying that the LMmode is applied to the current block, index information specifying the one of the plurality of LMmode candidates selected for the current block is additionally encoded into the bitstream, and the plurality of LMmode candidates comprises a first LMmode and a second LMmode,
wherein predicting the chroma pixel of the current block comprises:
obtaining a first filtered luma value to predict the chroma pixel;
obtaining a weight and an offset based on a linear relationship between luma pixels and chroma pixels; and
predicting the chroma pixel based on the first filtered luma value, the weight and the offset,
wherein, under the first LMmode, the weight and the offset are obtained based on a second filtered luma value, while, under the second LMmode, the weight and the offset are obtained in absence of the second filtered luma value,
wherein a horizontal neighboring luma pixel adjacent to a co-located luma pixel is relied on to derive the first filtered luma value and the co-located luma pixel having a position corresponding to the chroma pixel,
wherein the first filtered luma value is obtained based on a weighted sum operation using the co-located luma pixel and the horizontal neighboring luma pixel, and
wherein the chroma pixel is predicted by an equation C pred [x, y]=αG recon lpf [x, y]+β (wherein, G recon lpf [x, y] denotes the first filtered luma value, α denotes the weight, and β denotes the offset), and wherein the second filtered luma value is obtained based on a neighboring luma pixel.
6. The method of claim 5 , wherein the horizontal neighboring luma pixel comprises at least one of a left neighboring luma pixel and a right neighboring luma pixel.