Provided are a method and apparatus for encoding a picture, a method and apparatus for decoding a picture, an electronic device, and a system. The method for encoding a picture includes: determining a prediction value of an encoded block, and calculating a prediction residual between the encoded block and the prediction value; performing a transformation on the prediction residual at least once to obtain transform data, and determining transform coefficients using the transform data; determining a scanning mode of the transform coefficients and a size of the coefficient group of the transform coefficients, dividing the transform coefficients into at least one coefficient group, scanning transform coefficients comprised in each of the at least one coefficient group according to the scanning mode, and converting the transform coefficients into at least one syntax element; and encoding the size of the coefficient group and a value of the at least one syntax element, and writing encoded bits to a code stream.