Image encoding/decoding method and device for signaling filter information on basis of chroma format, and method for transmitting bitstream

1. An image decoding method performed by an image decoding apparatus, the image decoding method comprising:

determining a chroma array type of a current image;

determining an adaptive loop filter (ALF) indicator of a chroma component based on the chroma array type; and

performing ALF filtering with respect to a reconstructed image based on a value of the ALF indicator,

wherein the value of the ALF indicator is determined to be 0 without being obtained from a bitstream, based on the chroma array type being a monochrome type, and

wherein the value of the ALF indicator is obtained from the bitstream, based on the chroma array type not being the monochrome type.

2. The image decoding method of claim 1 , wherein the value of the ALF indicator is determined to be a value specifying that an ALF does not apply to a chroma component, based on the chroma array type being the monochrome type.

3. The image decoding method of claim 1 , wherein the performing ALF filtering with respect to the reconstructed image based on the value of the ALF indicator is performed by determining a chroma component, to which an ALF applies, according to the value of the ALF indicator.

4. The image decoding method of claim 1 , wherein the ALF indicator is included and signaled in a picture header or slice header of the bitstream, based on the chroma array type not being the monochrome type.

5. The image decoding method of claim 1 ,

wherein the ALF indicator is signaled as a first ALF indicator included and signaled in a picture header of the bitstream or a second ALF indicator included and signaled in a slice header of the bitstream, based on the chroma array type not being the monochrome type,

wherein the first ALF indicator is determined to be a predetermined value without being obtained from the picture header, based on the chroma array type being the monochrome type, and

wherein the second ALF indicator is determined to be a value of the first ALF indicator without being obtained from the slice header, based on the chroma array type being the monochrome type.

6. The image decoding method of claim 1 , further comprising determining a value of chroma filter signaling information specifying whether to signal filter information of a chroma component based on the chroma array type.

7. The image decoding method of claim 6 ,

wherein the determining the value of the chroma filter signaling information comprises obtaining, from the bitstream, a value of chroma syntax signaling information specifying whether a chroma related syntax element is included in an APS NAL unit,

wherein the value of the chroma syntax signaling information is determined to be a value specifying that the chroma related syntax element is not included in the APS NAL unit, based on the chroma array type being the monochrome type, and

wherein the chroma filter signaling information is determined to be a value specifying that filter information of the chroma component is not signaled without being obtained from the bitstream, based on the value of the chroma syntax signaling information being a value specifying that the chroma related syntax element is not included in an APS NAL unit.

8. The image decoding method of claim 6 , wherein the chroma filter signaling information is determined to be a value specifying that filter information of the chroma component is not signaled without being obtained from the bitstream, based on the chroma array type being the monochrome type.

9. An image encoding method performed by an image encoding apparatus, the image encoding method comprising:

determining a chroma array type of a current image; and

generating a bitstream by encoding an adaptive loop filter (ALF) indicator specifying a chroma component to which an ALF applies, based on the chroma array type of the current image,

wherein a value of the ALF indicator is not encoded, based on the chroma array type being a monochrome type, and

wherein the value of the ALF indicator is encoded, based on the chroma array type not being the monochrome type.

10. The image encoding method of claim 9 ,

wherein an ALF does not apply to a chroma component of the current image, based on the chroma array type being the monochrome type.

11. The image encoding method of claim 9 , wherein the ALF indicator is included and encoded in a picture header or slice header of the bitstream, based on the chroma array type not being the monochrome type.

12. The image encoding method of claim 9 , further comprising determining whether to signal filter information of a chroma component based on the chroma array type.

13. A method of transmitting a bitstream generated by an image encoding method, the image encoding method comprising:

determining a chroma array type of a current image; and

generating a bitstream by encoding an adaptive loop filter (ALF) indicator specifying a chroma component to which an ALF applies, based on the chroma array type of the current image,

wherein a value of the ALF indicator is not encoded, based on the chroma array type being a monochrome type, and

wherein the value of the ALF indicator is encoded, based on the chroma array type not being the monochrome type.