In this report we discuss the method of the analysis of pseudo-identical optical signals. Two similar images, composed by identical apertures, were taken as an example for examination. The difference in their structures can be connected with the value of the apertures' function of transmittance, with the inter-apertures' separation along one direction, or with both these factors simultaneously. The overall functions of the transmittance for this type of pseudo- identical structure can be measured up through comparison of the secondary Fourier spectrums of corresponding transmittance functions.