Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
  • H04N23/70—Circuitry for compensating brightness variation in the scene
  • H04N23/71—Circuitry for evaluating the brightness variation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
  • H04N23/70—Circuitry for compensating brightness variation in the scene
  • H04N23/745—Detection of flicker frequency or suppression of flicker wherein the flicker is caused by illumination, e.g. due to fluorescent tube illumination or pulsed LED illumination

Definitions

• the invention concerns method of regulation of photographic camera shutter release if the photographed object is illuminated from an artificial light source powered by alternate current. This method is mainly designed for assurance of equal illumination of each of a series of photographs. The invention further concerns equipment for execution of this method.
• the exposition time is comparable with the power voltage oscillation period or considerably longer, then the illumination intensity oscillations exercise no significant effect on the resulting photograph. If, however, the exposition time is considerably shorter than the power voltage oscillation period then the result depends on the illumination intensity phase in which the camera shutter opens. If the shutter opens when the intensity of illumination of the photographed object is maximal, then the image may be overexposed while if the shutter opens when the intensity of illumination of the photographed object is minimal, then the image may be underexposed.
• This release does not provide any interaction with the visual signal, i.e. does not set automatic synchronisation with the progress of the light wave.
• the practical result is that a series of more photographs of the same scene illuminated with oscillating light will show different results under constant exposition conditions for the reason of different integration of the luminous energy depending on the moment of opening and closing of the exposition shutter.
• the phenomenon only ceases in the case of longer exposition times when the mean exposition value does not depend on the phase of the shutter release. In daylight or in the case of illumination with high-frequency sources (exchangers) or direct current sources this phenomenon does not occur.
• Another possible but unacceptable method is acquisition of a large number of pictures and production of the resulting image by averaging. This, however, is more time demanding with little guarantee of results of the required quality.
• the size of the electrical signal corresponding to the photographed object illumination intensity is directly proportional to the photographed object illumination intensity.
• the electrical signal phase for the camera shutter release is specified in order to achieve the shutter opening around the peak value of the electrical signal, which is directly proportional to the photographed object illumination intensity.
• an amplifier and/or shaper of the photographed object illumination intensity sensor output signal is inserted between the photographed object illumination intensity sensor output and the oscillating luminous wave phase detector input.
• One of the pair of outputs of the amplifier/shaper is connected to the oscillating luminous wave phase detector input and the other to the second input of the logical circuit.
• the photographed object illumination intensity sensor is preferably produced as a direction selective photodiode and in another preferred embodiment equipped with an input diaphragm for regulation of the photographed object illumination intensity sensor angle of view.
• the amplifier and/or shaper of the photographed object illumination intensity sensor output signal includes a quick trans-impedance amplifier.
• the photographed object illumination intensity sensor output signal amplifier/shaper further includes a peak rectifier with its input connected to the quick trans-impedance amplifier output and its output connected to the input of a filter, the first output of the photographed object illumination intensity sensor output signal amplifier/shaper being the output of the quick trans-impedance amplifier connected to the first input of the logical circuit and the second output of the photographed object illumination intensity sensor output signal amplifier/shaper being the output of the filter connected to the phase detector input.
• the phase detector includes a voltage attenuator and the logical circuit includes a comparator with its output connected to a mono- stable circuit.
• fig. 1 shows a schematic drawing of a preferred embodiment of the equipment for regulation of the camera shutter release moment pursuant to the invention
• fig. 2 shows a more detailed schematic drawing of the preferred embodiment of the equipment for regulation of the camera shutter release moment pursuant to the invention pursuant to fig. 1.
• a preferred embodiment of the method of regulation of photographic camera shutter release for the purpose of uniform illumination of each of a series of photographs if the photographed object is illuminated from an artificial light source powered by alternate current and the exposition time is shorter than approximately double the frequency of the alternate current source will be described below.
• the progress of the photographed object illumination intensity is measured and the measured values are transformed to electrical signal of a size proportional at every moment to the value of the momentary intensity of illumination of the photographed object.
• the method needs simultaneous or previous specification of the phase of the oscillating electrical signal at which the camera shutter will be released. Then the shutter unblocks as soon as the electrical signal reaches the specified phase.
• the size of the electrical signal corresponding to the photographed object illumination intensity is as a rule directly proportional to the photographed object illumination intensity. However, the electrical signal may be encoded or its size may be indirectly proportional to the illumination intensity. What is essential is that a value of the photographed object illumination intensity phase must be allocable to each electrical signal value.
• FIG. 1 schematically shows a general embodiment of the equipment for execution of the regulation method for camera shutter release pursuant to the present invention.
• This equipment includes a photographed object illumination intensity sensor 1 whose output is connected via an amplifier/shaper 2 of the output signal of the photographed object illumination intensity sensor to an oscillating luminous wave phase detector 3.
• the output of the detector 3 is connected to one of the pair of inputs of a logical circuit 5 whose second input is connected to the output of a manual camera release 4.
• the output of the logical circuit 5 is connected to the camera shutter activator 6.
• the logical circuit 5 is designed for transmission of the trigger signal to the activator 6 on the basis of evaluation activity of the manual camera 3 ⁇ 4 release 4 and the phase detector 3, i.e. at the moment of simultaneous triggering of the manual release 4_and detection of achievement of the specified phase of the electrical signal for the camera shutter release.
• Fig. 2 schematically shows a preferred embodiment of the equipment for execution of the regulation method for camera shutter release pursuant to the present invention.
• This equipment includes a photographed object illumination intensity sensor 1 whose output is connected via an amplifier/shaper 2 of the output signal of the photographed object illumination intensity sensor 1. to ah oscillating luminous wave phase detector 3.
• the output of the detector 3 is connected to one of the pair of inputs of a logical circuit 5 whose second input is connected to the output of an amplifier/shaper 2 of the photographed object illumination intensity sensor 1_ output signal.
• the output of the logical circuit 5 is connected to the manual camera release 4 whose output is connected to the camera shutter activator 6.
• the logical circuit 5 is designed for transmission of the trigger signal to the activator 6_via the manual release 4, i.e. at the moment of simultaneous triggering of the manual release 4 and detection of achievement of the specified phase of the electrical signal for the camera shutter release.
• Fig. 3 schematically shows a more detailed representation of the same preferred embodiment of the equipment for execution of the regulation method for camera shutter release pursuant to the present invention.
• the amplifier/shaper 2 of the output signal of the photographed object illumination intensity sensor 1_ includes a quick trans-impedance amplifier 7, whose output is connected to an input of a peak rectifier 8, whose output is connected to the input of a filter 9. The output of the filter is grounded via a voltage attenuator 10.
• One of the pair of inputs of the comparator H is connected to an output of the quick trans-impedance amplifier 7 while the other input of the comparator 1_1 > s connected to an output of the voltage attenuator 10.
• the output of the mono-stable circuit 12 is connected via the manual release 4 to the control input of the shutter activator 6.
• the photographed object illumination intensity sensor ⁇ is produced as a direction selective photodiode or another sensing element reacting to the momentary illumination value, or brightness in the given direction, ideally in the direction of the photographed scene. Selection of a diaphragm for the direction selective filter can select the viewing angle defining the acceptance field of the sensor and thus the size of the sensed surface.
• the current signal from the photographed object illumination intensity sensor 1 corresponding to the momentary value of the sensed illumination quantity or brightness is amplified and transformed to voltage in the trans-impedance amplifier 7.
• the signal branches after the amplifier 7.
• One branch is connected to the peak rectifier_8 designed to acquire DC value of the voltage corresponding to the maximum value of the input signal at the output.
• the rectified signal is filtered with the filter 9 circuit.
• At its output there is DC voltage corresponding to the peak value of the signal after the trans-impedance amplifier 7.
• This signal is further selectively attenuated to the required level with the voltage attenuator 10, thus defining the size of the comparative signal level for the comparator 11..
• the other input of the comparator 11_ is directly actuated by the signal from the trans-impedance amplifier 7.
• the comparator 11 After the comparator 11 , there is a rectangular signal where the commencing edge of the signal means exceeding of the governing level and identified the selected phase of the originally optical signal. This edge triggers the mono-stable circuit
• the equipment for execution of the regulation method for camera shutter release pursuant to the present invention provides positive synchronisation of the oscillating light with the exposition mechanism, thus assuring constant conditions for exposition of a series of the same images.
• the phase selection allows changing the ratio of exposition with the input signal in relation to the delay of the camera shutter.
• the essence of the solution is detection of oscillating illumination on the camera objective level and generation of a synchronisation pulse for the camera release or shutter on the basis of the selected time delay. This system is thus able to assure virtually constant exposition conditions in oscillating light which might otherwise lead to significant differences in a series of images acquired with the same exposition regime.
• Light sources powered from standard AC 50 Hz grids generate luminous flux changes and thus illumination changes with the frequency of 100 Hz.
• the equipment for execution of the regulation method for camera shutter release pursuant to the present invention eliminates exposition faults caused by light oscillation, thus providing qualitatively better conditions for acquisition of photographs under artificial lighting.
• the equipment for execution of the regulation method for camera shutter release pursuant to the present invention assures equal results of acquisition of a series of images with the same exposition parameters in the form of photographs with the same brightness level.
• this circuit it is possible to acquire images with high luminance dynamics with the help of exposition regime changes without the risk of erroneous recalculations of the individual images, because all images can use the same median illumination value as the comparative value.
• the method and the equipment thus guarantee reproducibility of pictures taken with manual release under constant conditions of the scene and illumination despite the oscillating light emitted from artificial sources powered from standard alternate current sources 50 or 60 Hz.
• the invented circuit can be used not only in photographic cameras but also in other optical recording devices for more accurate synchronisation of the shutter where the difference between image acquisition frequency and light oscillation creates interferential blinking of the image.
• the invented circuit might help synchronise the shutter for achievement of a constant median value.
• the method of regulation of photographic camera shutter release and the equipment for execution of this method can be used for manufacture of photographic cameras, especially those used for acquisition of series of industrial photographs for example when imaging individual phases of fast actions.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Studio Devices (AREA)
• Exposure Control For Cameras (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Citations (6)

Family Cites Families (3)

• 2010
  • 2010-11-08 CZ CZ20100805A patent/CZ303282B6/cs not_active IP Right Cessation
• 2011
  • 2011-11-08 WO PCT/CZ2011/000107 patent/WO2012062230A1/en not_active Ceased

Patent Citations (6)

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