In fluorescence imaging, both fluorescence yield and lifetime are of great importance. Traditionally, with the frequency-domain data, two parameters can be directly recovered through a nonlinear formulation. However, the reconstruction accuracy highly depends on initial guesses. To overcome this hurdle, we propose the linear scheme via an inverse complex-source formulation. Using the real and imaginary parts of the frequency-domain data, the proposed method is fully linear; it is not sensitive to initial guesses and is stable with high-level noise. Meanwhile, the algorithm is efficient, and the reconstruction takes one or a few iterations. In addition, the colocalization constraint due to the unique feature of fluorescence imaging is imposed to enhance algorithm performance. The algorithms are tested with simulated data.