An apparatus for coding an image is provided to effectively code the image. The apparatus for coding the image includes an input image segmentation unit to segment an input image into a plurality of image blocks including a first image block and a second image block. The apparatus also includes a waveform information generation unit to select a plurality of reference pixels from among pixels included in the first image block, generate first waveform information about the first image block based on a pixel value difference between the selected plurality of reference pixels, and generate second waveform information about the second image block based on a pixel value difference between the pixels included in the second image block. The apparatus also includes a coding unit to code an image included in the second image block based on the first waveform information and the second waveform information.