Method and device for encoding or decoding image

An encoding method comprising:

• obtaining a first bin string by binarizing a value of a first syntax element;
• obtaining first probability information for performing arithmetic encoding on a first bin among the first bin string regarding the first syntax element based on a first probability model and a second probability model;
• obtaining a first bitstring regarding the first syntax element by performing arithmetic encoding on the first bin based on the obtained first probability information;
• obtaining a second bin string by binarizing a value of a second syntax element;
• obtaining second probability information for performing arithmetic encoding on a second bin among the second bin string regarding the second syntax element based on a third probability model and a fourth probability model;
• and
• obtaining a second bitstring regarding the second syntax element by performing arithmetic encoding on the second bin based on the obtained second probability information,
• wherein the first probability model is determined based on a first bit-shift value, the second probability model is determined based on a second bit-shift value, the first bit-shift value is determined based on a first shift index and the second bit-shift value is determined based on the first bit-shift value and the first shift index, wherein the third probability model is determined based on a third bit-shift value, the fourth probability model is determined based on a fourth bit-shift value, the third bit-shift value is determined based on a third shift index and the fourth bit-shift value is determined based on the third bit-shift value and the third shift index.