In addition, the predetermined boundary line may be a straight line extending in a different direction from the first direction and the second direction that define the plane. For example, the predetermined boundary line may be a straight line extending in a direction perpendicular to a line that bisects an angle formed by the first direction and the second direction.

Also, the origin point on the 2D plane may denote an intersection point of a frequency axis in the first direction and a frequency axis in the second direction at the upper left end of FIG. 3B.

FIGS. 4A to 4C are diagrams showing examples of a frequency filter according to an embodiment.

FIGS. 4A and 4B illustrate a variation in characteristics of the frequency filter according to a location of a boundary line 410. For example, as shown in FIG. 4B, when the boundary line 410 is close to the origin point, a relatively small number of the high frequency components are included in the output image, the quality of the output image degrades, and the bitrate of the output image also decreases. Thus, when a difference between the current bitrate and the target bitrate is relatively large, a frequency filter having the boundary line 410 close to the origin point as in FIG. 4B may be used to overcome the difference.

Referring to FIG. 4B, a boundary line 411 is close to the origin point. When the above frequency filter is applied to the magnitudes of one or more frequency components, the output image only includes three frequency components, which will be described later.