1. An image encoding apparatus that divides image data into a plurality of tiles and performs encoding for each tile, the apparatus comprising: a transformation unit configured to perform, for each tile, a wavelet transform and obtain transformation coefficient data; and an encoding unit configured to encode, for each tile, the transformation coefficient data obtained by the transformation unit, wherein, if a neighboring tile that neighbors an encoding target tile is present, the transformation unit obtains the transformation coefficient data by performing the wavelet transform with reference to pixel data of the encoding target tile and a plurality of pieces of pixel data that neighbor the encoding target tile out of the neighboring tile, and the encoding unit, out of the transformation coefficient data obtained by referring to the plurality of pieces of pixel data of the neighboring tile, encodes at least transformation coefficient data necessary to decode the pixel data of the encoding target tile, and does not encode a portion of the transformation coefficient data obtained by the transformation unit.