1. An image encoding method using color space estimation, which encodes a current pixel according to directionality of neighbor pixels and a size of a residual component, the method comprising: encoding a pixel of a first color space; selecting an estimation mode of the current pixel from a color space estimation mode and a space estimation mode by taking into account the directionality of the neighbor pixels respect to the current pixel of a second color space and the size of the residual component between a current pixel value and a neighbor pixel value; calculating an estimation value according to the selected estimation mode; and encoding a difference value of the calculated estimation value and the current pixel value.