A method of compressing an image signal, the method comprising: performing a partial exchange between rows and between columns of a transform matrix; transforming the image signal that is to be compressed by using the transform matrix in which the partial exchange has been performed; compressing the transformed image signal; and selecting an angle parameter corresponding to a highest compression rate by repeating the performing the partial exchange, the transforming the image signal, and the compressing the transformed image signal, by applying several values to angle parameters showing extents the partial exchanges between the rows and between the columns of the transform matrix, wherein the partial exchange means rows or columns of a transform matrix are partially exchanged according to values of the angle parameters, wherein the partial exchange is performed when the values of the angle parameters are greater than 0° and less than 90°, or greater than 90° and less than 180°; and the selecting the angle parameter corresponding to the highest compression rate comprises: generating a random sequence with regards to the angle parameter; obtaining a compression rate of the image signal by performing the partial exchange between the rows and between the columns, the transforming of the image signal, and the compressing of the transformed image signal on each value of the random sequence; obtaining the highest compression rate from among the obtained compression rates of each value of the random sequence; and selecting a value of the angle parameter corresponding to the highest compression rate, wherein the generated random sequence is a Lehmer pseudo-random number. performing a partial exchange between rows and between columns of a transform matrix; transforming the image signal that is to be compressed by using the transform matrix in which the partial exchange has been performed; compressing the transformed image signal; and selecting an angle parameter corresponding to a highest compression rate by repeating the performing the partial exchange, the transforming the image signal, and the compressing the transformed image signal, by applying several values to angle parameters showing extents the partial exchanges between the rows and between the columns of the transform matrix, wherein the partial exchange means rows or columns of a transform matrix are partially exchanged according to values of the angle parameters, wherein the partial exchange is performed when the values of the angle parameters are greater than 0° and less than 90°, or greater than 90° and less than 180°; and the selecting the angle parameter corresponding to the highest compression rate comprises: generating a random sequence with regards to the angle parameter; obtaining a compression rate of the image signal by performing the partial exchange between the rows and between the columns, the transforming of the image signal, and the compressing of the transformed image signal on each value of the random sequence; obtaining the highest compression rate from among the obtained compression rates of each value of the random sequence; and selecting a value of the angle parameter corresponding to the highest compression rate, wherein the generated random sequence is a Lehmer pseudo-random number. generating a random sequence with regards to the angle parameter; obtaining a compression rate of the image signal by performing the partial exchange between the rows and between the columns, the transforming of the image signal, and the compressing of the transformed image signal on each value of the random sequence; obtaining the highest compression rate from among the obtained compression rates of each value of the random sequence; and selecting a value of the angle parameter corresponding to the highest compression rate, wherein the generated random sequence is a Lehmer pseudo-random number.