<P> In the case of photographic film and magnetic tape, noise (both visible and audible) is introduced due to the grain structure of the medium . In photographic film, the size of the grains in the film determines the film's sensitivity, more sensitive film having larger sized grains . In magnetic tape, the larger the grains of the magnetic particles (usually ferric oxide or magnetite), the more prone the medium is to noise . </P> <P> To compensate for this, larger areas of film or magnetic tape may be used to lower the noise to an acceptable level . </P> <P> Many noise reduction algorithms tend to alter signals to a greater or lesser degree . The local signal - and - noise orthogonalization algorithm can be used to avoid changes to the signals . </P> <P> Boosting signals in seismic data is especially crucial for seismic imaging, inversion, and interpretation, thereby greatly improving the success rate in oil & gas exploration . The useful signal that is smeared in the ambient random noise is often neglected and thus may cause fake discontinuity of seismic events and artifacts in the final migrated image . Enhancing the useful signal while preserving edge properties of the seismic profiles by attenuating random noise can help reduce interpretation difficulties and misleading risks for oil and gas detection . </P>

Which of the following in an image can be removed by using smoothing filter