1. A method of intra predicting an image, the method comprising: obtaining, by using at least one adjacent pixel located upper right to a current prediction unit, a first virtual pixel located on a same line as a current predicted pixel of the current prediction unit while corresponding to a pixel located farthest right of the current prediction unit; obtaining, by using at least one adjacent pixel located lower left to the current prediction unit, a second virtual pixel located on a same column as the current predicted pixel while corresponding to a pixel located farthest below the current prediction unit; obtaining a first prediction value of the current predicted pixel via linear interpolation using the first virtual pixel and an adjacent left pixel on the same line as the current predicted pixel; obtaining a second prediction value of the current predicted pixel via linear interpolation using the second virtual pixel and an adjacent upper pixel on the same column as the current predicted pixel; and obtaining a prediction value of the current predicted pixel by using the obtained first prediction value and the obtained second prediction value.