The targets of intensity mapping do not need to be limited to strong emission lines. I will introduce a cross-correlation-based method to recover previously collapsed redshift information for cosmic photons in intensity maps of arbitrary bandwidths. This represents a tomography not only in line-of-sight distance (or cosmic time) but also in frequency space as the photons get redshifted by the cosmic expansion. I will demonstrate this method with data by probing the continuum, Lyα line, and Lyman break in the cosmic UV background up to z~2 using GALEX All Sky and Medium Imaging Surveys. This allows us to perform spectral diagnostics for the entire body of the UV background and provide insights on cosmic star-formation, black hole accretion, and potential emission from the diffuse intergalactic medium. We expect this method to be generically applicable for a rich set of existing and upcoming wide-field datasets in probing the cosmic background over a wide range of wavebands up to cosmic high noon.