An amplification-factor of the amplifier is controlled so as the output from a film-detecting-mechanism to be supplied as the input into a subtractor is adjusted fitting to a reference signal-prior to the film-insertion into the detecting mechanism. The output-signal from a comparator is supplied into the amplification-factor-variable-amplifier, in which the amplification-factor is controlled depending on the magnitude of the input-signal, and it is kept at the controlled value. Or an intensity of a light source is controlled so as the output from the film detecting mechanism to be supplied as the input into the subtractor is adjusted fitting to the reference-signal prior to the film-insertion into the detecting mechanism.
In a measurement device of photographic density of a film wherein a light source is provided on one side over a film carrier route and a plurality of light receiving elements for converting transmitted light of a film emitted from the said light source to an electrical signal are provided on the counter side of the light source forming a line, a device for measuring photographic density of the film comprising a means for obtaining a rate of change in the form of a ratio between a reference signal decided beforehand for each of the light receiving elements and an output signal of the light receiving elements when the film is carried, and a means for obtaining photographic density of the film in accordance with the obtained ratio.
A photometer head for measuring light transmission of a strip of photographic material has a base plate on which are mounted two housing portions. The housing portions have facing wall portions that are spaced apart to form a gap for receiving the strip, the base plate forming the bottom of the gap. The housing portions contain light source means for directing light to the gap and light sensitive means to receive light passing through the strip from the light source.
In order to detect the presence and make measurements of the dimensions of web which travels along a path, for example film, such as X-ray film and equipment which develops such film, a linear array of light emitting devices (e.g. LEDs) is disposed opposite to an array of corresponding photodetectors to define a gap through which the web travels. The web is scanned by sequentially applying pulses of electrical power to the emitting devices. Output signals are provided from each photodetector representing the presence of the web. In order that the brightness is sufficient to detect the presence of low density (semi-opaque) webs and to maintain uniformity of brightness of illumination from emitter to emitter, the current to the emitters is computer controlled by means of a control system which responds to the signals from the photodetectors and increments or decrements the current from an initially preset level during selected scans, for example on scans which occur every 15 seconds. The preset level is sufficient so that the photodetectors detect a substantial reduction in illumination and provide corresponding output signals even when blocked by a semi-opaque film. The width of the web may be determined by counting the number of photodetectors producing these output signals during each scan and the web area passing through the detection arrays may be determined by counting output signals representing the detection of the web. In X-ray film development when a count is registered corresponding to a predetermined area of film, the developing chemicals are replenished.
