1. An image data filtering apparatus for reducing a blocking effect and noise, the apparatus comprising: an obtainer which obtains a data block including transformed coefficients; a filtering information generator which checks whether all coefficients of all pixels in the data block are equal to zero or not, and generates filtering information indicating whether to perform deblocking filtering for the data block according to whether all of the coefficients of all of the pixels in the data block are equal to zero or not; and a filtering unit which filters the data block passed through inverse quantization and inverse transform according to the generated filtering information.