PURPOSE: To perform continuously and precisely the measurement of density from a low density part to a high density part by switching the quantities of light projected upon an X-ray film according to the density of the X-ray film.
CONSTITUTION: Light I0 from a light source 1 is converted by a light-quantity varying element 2 into a light beam with a quantity I0 or I0/n and the quantity of light transmitted through the X-ray film 5 is converted into an electric signal by a photoelectric converter 7. Namely, the light beam is projected upon the high-density part A and low density part B of the X-ray film 5 to the quantities I0 and I0/n, respectively. The electric signal is inputted to a comparator 10 and a logarithmic converter 11 through a current-voltage converter 8. The comparator 10 compares the input voltage signal Vd with the light-quantity switching level V0 of a level setter 9 and generates a signal when Vd is less than V0. An adder 12 adds 1/n to the output of the logarithmic converter 11 at the time of the projection light of I0 and the sum is stored in a sample holding (SH) circuit 15 and also stored in an SH circuit 14 directly. The measurement signal of the high-density part or low density part of the SH circuit 15 or 14 is outputted through a switch 16 according to whether the comparator 10 generates the output or not.
ISHIKAWA KEN
WATABE SHIGERU
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