1. A method for calculating, in a computing device, angle domain common image gathers (ADCIGs) for use in generating a final image of a subsurface of the earth, the method comprising: calculating with wavefield forward propagation, in a time-space domain, a source wavefield p F of a seismic source; calculating with wavefield back propagation, in the time-space domain, a receiver wavefield p B of a seismic receiver configured to detect a seismic wave generated by the seismic source, wherein the seismic wave emitted by the seismic source enters the subsurface of the earth and gets reflected on a reflector of the subsurface prior to arriving at the seismic receiver; applying an algorithm of anti-leakage Fourier transform (ALFT) to transform the source wavefield p F to a wavenumber domain; applying the ALFT algorithm to the receiver wavefield to transform the receiver wavefield in the wavenumber domain; determining an imaging condition to the ALFT source and receiver wavefields in the wavenumber domain; computing a reflection angle Î¸ and an azimuth angle Ï† of the source wavefield p F and receiver wavefield p B in the wavenumber domain; calculating the ADCIGs in the wavenumber domain; and applying an inverse fast Fourier transform (FFT) to determine the ADCIGs in the space domain.