We have obtained the density or x-ray tube voltage dependence of the Wiener spectra of the three factors of radiographic mottle, i.e., quantum mottle, structure mottle, and film granularity, for the double emulsions of the x-ray film. For the purpose, we proposed a method for obtaining the Wiener spectrum of each of the three factors for the double emulsions. To investigate the relation between the Wiener spectra of the quantum mottle for the double and single emulsions, we compared the Wiener spectra of the quantum mottle for the double emulsions with the sum of those for the front and back emulsions on the same radiographs. The Wiener spectral values of the quantum mottle for the double emulsions at 0 mm$+$MIN@1$/ were greater than the sums of the Wiener spectral values of the quantum mottle for the front and back emulsions at tube voltages of 50 to 100 kV. We found that this was the result which originated from the following phenomena: (1) the noise-equivalent numbers of quanta (NEQ) of the dual screens were roughly equal to the sum of the NEQ of the front and back screens; (2) the squares of the gradients for the double emulsions were more than four times on an average as great as those for the front and back emulsions.
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