CPC H04N 19/42 (2014.11) [H04N 19/124 (2014.11); H04N 19/146 (2014.11); H04N 19/176 (2014.11); H04N 19/18 (2014.11); H04N 19/48 (2014.11)]  11 Claims 
1. A method of adjusting a bitrate of an image frame, the method comprising:
identifying magnitudes of one or more frequency components in the image by performing a twodimensional (2D) discrete cosine transformation (DCT) on the image, and arranging the magnitudes of the one or more frequency components on a 2D plane in a first direction and a second direction of the image;
determining a frequency filter based on a difference between a current bitrate and a target bitrate of the image, wherein the frequency filter reduces magnitudes of frequency components other than magnitudes of frequency components existing between an origin point and a predetermined boundary line on the 2D plane;
wherein the predetermined boundary line is a straight line extending in a direction different from the first direction and the second direction, and the first direction and the second direction are perpendicular to each other;
wherein the frequency filter consists of two constant values comprising:
a first filter value corresponding to each of the frequency components existing between the origin point and the predetermined boundary line on the 2D plane; and
a second filter value corresponding to each of the frequency components other than the frequency components existing between the origin point and the predetermined boundary line on the 2D plane;
determining the number of low frequency components in the frequency filter having the first filter value, from the difference between the current bitrate and the target bitrate of the image, while values of the frequency filter remain unchanged, wherein as the difference between the current bitrate and the target bitrate increases, more number of high frequency components are excluded by the frequency filter and as the difference between the current bitrate and the target bitrate decreases, less number of high frequency components are excluded by the frequency filter;
applying the determined frequency filter to the magnitudes of the one or more frequency components in real time;
generating, in advance, the frequency filters corresponding to the difference between the current bitrate and the target bitrate;
storing the frequency filters in advance in a memory;
selecting in real time, the frequency filter stored in the memory, corresponding to real time difference between the current bitrate and the target bitrate, and applying the selected filter to the magnitude of the frequency component;
wherein the image comprises a plurality of image blocks; and
wherein the determining the frequency filter comprises determining a frequency filter corresponding to a difference between an output bitrate and a target bitrate of each image block, with respect to each of the at least one image block.
