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
  • H04N23/56—Cameras or camera modules comprising electronic image sensors; Control thereof provided with illuminating means
• • 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
  • H04N23/74—Circuitry for compensating brightness variation in the scene by influencing the scene brightness using illuminating means

Definitions

• the invention relates to a lighting device for objects that are recorded by a camera that has at least one CCD image sensor, the image signal of which is applied to an image processing device, with a light source that controls a control unit in pulse mode.
• an important influencing variable is the quality of the recorded image signal.
• the type of lighting device is an important factor here:
• An alternative to permanent lighting in video cameras with a holding capacity for the charge image is the case with CCD cameras, are lighting devices which have flash or stroboscopic light sources. These devices provide a high radiation power periodically for a short time, namely in the blanking interval between the images of the video image. The electrical power required on average is thus considerably lower than the electrical power that would be expended in a CCD camera with an electronic shutter device, in which illumination is carried out with continuous light.
• Known flash or stroboscopic lighting devices which work with xenon flash lamps, for example, are power-efficient and eliminate the aforementioned disadvantages in the case of moving image recording. There are, however, work-physiological reasons that speak against the use of such stroboscopes: Xenon flash lamps, for example, light up in the visible range. Therefore, working in their environment is perceived as unpleasant.
• EP-A-0 181 412 a lighting device for objects that are recorded by a camera that has at least one CCD image sensor is known according to the preamble of patent claim 1.
• This known generic lighting device has a pulsed infrared radiator as the light source, which can be, for example, a light-emitting diode or a laser diode.
• the known lighting devices for objects that work with flash lamps or a pulsed diode only allow the integral lighting of the object to be recorded; Furthermore, an adjustment of the brightness with which the object is illuminated is not provided in the lighting device known from EP-AO 181 412.
• Illumination devices that enable selective illumination would, as a rule, mean an unacceptable effort due to the use of a number of flash lamps or a corresponding number of fast closures in the beam path. But even if several biltz lamps were used, there would be no possibility of adjusting the brightness, or it would be possible to implement them only with great effort. Presentation of the invention
• the invention is based on the object of providing an illumination device for objects which are picked up by a camera and which has at least one CCD image sensor, the image signal of which is applied to an image processing device which, in the case of rapidly moving objects, which is selective and with adjustable brightness should be illuminated, an image recording without motion blurring with a light source allows comparatively low power consumption.
• the light source has a light-emitting diode array, the diodes of which are selectively acted upon by the control unit with at least one pulse of variable width during each image period.
• selective lighting is achieved in that the light source - in a manner known per se - from many small, individually or in groups (claim 4) by means of an internal control unit, a process computer (claim 9) or manually (claim 8) controllable individual light sources consists.
• light emitting diodes are used as individual light sources, since light emitting diodes combined in arrays can be comparatively inexpensively produced and can also be controlled by a control unit, which can also be constructed comparatively inexpensively (claims 12 and 13).
• a control unit which can also be constructed comparatively inexpensively (claims 12 and 13).
• light-emitting diodes without major problems are suitable for pulse operation, by means of which a strobe effect is achieved.
• Incandescent or halogen lamps are not suitable for this application as a light source since they are not suitable for pulse operation. They have a very low switch-on input resistance, which in the short term leads to very high temperatures in the filament and thus to premature destruction.
• Xenon flash lamps on the other hand, have the disadvantages mentioned above.
• the control unit provides synchronous pulses with the video signal, the width of which can be selected within certain limits. In typical applications, the width of the pulses is between 4 and 400 ⁇ sec. The width of the pulses enables the light energy per pulse and thus the average brightness to be set.
• a light pulse is emitted every 20 msec, while in the case of an image processing device which processes frames, i.e. With a camera operating in frame integration mode, a light pulse is only generated every 40 msec. It is particularly preferred if the lighting device according to the invention can be switched between the two modes, so that it can be used with any image processing devices and cameras (claim 14).
• the design according to the invention provides an illumination device which has all the advantages of stroboscopes without having their disadvantages or the disadvantages of conventional illuminations, and which moreover permits selective illumination of a scene with adjustable brightness.
• the diodes emit light in the near infrared range between 850 and 1000 nm. Since the emitted light is thus outside the visible spectral range, but within the sensitive spectral range of most CCD cameras, a work-physiologically undesirable disturbance of the Avoid surroundings during pulse operation.
• Claim 3 states that the diodes are GaAs light-emitting diodes or GaAlAs light-emitting diodes. These light-emitting diodes have small geometric dimensions and are outstandingly suitable for pulse operation. During pulse operation, these light-emitting diodes can be loaded with a much higher current than would be possible with continuous operation, provided the ratio of the duty cycle to the period does not exceed a diode-specific maximum amount. There is an almost linear relationship between the electrical current flow and the emitted radiation, so that high beam powers can be achieved in this operating mode. Since the emitted spectrum is in the near infrared (850-1000 nm), the pulsed brightness fluctuations are not visible to humans. In addition, LEDs generally have a very long life expectancy. It is on average in the range of many years, so that the reliability is very high.
• diodes of the array are combined into groups or segments, and that the groups or segments can be controlled individually.
• a separate power level for each segment drives the individual light-emitting diodes of a segment.
• the light-emitting diodes can be arranged in any arrangement, for example in a matrix (claim 5) and combined to form smaller groups or segments. For example, the diodes can be grouped together in one row.
• the diodes can be arranged concentrically in several rings for illuminating rotationally symmetrical objects (claim 6).
• Each ring can consist of several, individually controllable segments (claim 7).
• the light of the light-emitting diodes is coupled into light guides which add the light from the individual diodes of the light-emitting diode array of the scene to be illuminated.
• the duration of the impulses affecting a group can be done manually (claim 8) or by means of a process computer (claim 9), for example via a V24 interface (claim 10).
• the design according to the invention provides an extremely flexible lighting device which has a number of advantages over conventional devices:
• the pulse-shaped lighting is easy to synchronize with the video signal, so that the lighting occurs only in the blanking interval between the images of the video image.
• the periodic fluctuations in brightness are invisible in the preferred embodiment according to claim 2, since the emitted spectrum is in the near infrared.
• the illumination is independent of the ambient light.
• the geometrical arrangement of the light-emitting diodes can be freely selected, so that the lighting device according to the invention can also be used in places that are difficult to access — optionally with additional light guides.
• the light emitting diodes used have a very long service life.
• FIG. 1 shows a block diagram of the control unit
• FIG. 2 shows a block diagram of the power driver
• FIGS. 3 to 5 light-emitting diode arrangements used according to the invention.
• the control unit shown in FIG. 1 is intended to deliver one pulse of variable width per video field, with which light-emitting diodes (not shown in FIG. 1) are actuated. If light-emitting diodes, as are typically used for a lighting device designed according to the invention, are to be loaded with a current of, for example, 1.1 A, the operating time for such diodes may e.g. amount to a maximum of 1/50 of the period.
• a pulse duration of 400 ⁇ s is referred to (in the exemplary embodiment shown) as a 100% pulse width.
• a two-stage programmable BCD down counter ZI is provided, which counts in the 8-4-2-1 code.
• the counter ZI is clocked at 250 kHz via a gate circuit TO and an oscillator 01.
• the pulse duration can be reduced in steps of 1%, ie from 4 ⁇ s to zero become.
• a counting step therefore corresponds exactly to the time of 4 ⁇ s.
• a counting cycle is started by the vertical video synchronization pulse.
• the BAS video signal is applied to a decoder D1, which is followed by a monoflop Ml, which shortens the pulse to approximately 100 ns.
• This signal loads a number in the BCD code, which can be set from the outside in a manner which will be explained in the following, and which is between 0 and 99 in the exemplary embodiment shown, as the beginning of the count in the counter ZI and at the same time sets an RS flip-flop FF1, that starts the counter oscillator 01.
• a multiple of 4 ⁇ s passes until the counter value reaches zero.
• the counter ZI indicates the zero crossing by means of a transmission pulse. This transmission pulse serves to reset the flip-flop FF1 and thus to stop the counter oscillator 01. This state remains stable until the next vertical sync pulse occurs. The entire cycle described above is then repeated periodically in synchronism with the video signal. The desired signal thus results at the output connection of the flip-flop FF1.
• the pulse width can be entered directly in percent with respect to the maximum permitted pulse width.
• the counter can switch in manual mode using BCD coding co e * L ner un ⁇ ** - co ze omputer ut> he inverting driver ⁇ gradually to both counters of the BCD counter ZI be set. It is also possible to use a process computer (not shown), for example via a V24 interface and a downstream serial Parallel converter (UART) on an 8-bit data bus.
• the counter reading is not read out from the coding switches, but from registers R in parallel.
• a control unit assigns the parameters to the individual registers. If a separate control unit is provided for each individual segment, simultaneous different power control of the segments or groups of light-emitting diodes is also possible.
• Driver stages and registers are provided with tri-state outputs so that they do not influence each other.
• the counter reading and thus the brightness are shown on a seven-segment display A.
• the gate circuit TO connected downstream of the oscillator 01 enables the entire lighting to be switched on and off asynchronously by hand or by the controlling computer.
• the power drivers have to switch very high currents for a short time without putting too much strain on the control unit. In addition, it must be possible to explicitly select the individual segments.
• AND gates "&" are provided on the input connections of the driver stages. These pass on the input signal to the drivers explained in more detail below only if they either by DIP switches and inverting drivers (manual operation) or by the corresponding bit in the segment register TS, which is affected by an 8 bit acted upon by the V24 interface Data bus (computer drive) has been selected.
• the AND gates & are equipped with open collector outputs so that higher currents can also flow.
• the driver stages themselves have transistors T1 and T2 in the so-called Darlington circuit, so that the required current amplification can be achieved.
• Transistor T1 is a transistor of the small signal type, while transistor T2 is a power transistor.
• In the collector circuit of T2 there is a light-emitting diode segment with e.g. ten diodes Dl ... Dn.
• a resistor R3 limits the current through this LED segment.
• the entire power stage is fed by a correspondingly high voltage, the individual drivers being connected in parallel in terms of power.
• the power supply unit consists of a regulated power supply unit which has two separate regulations for the voltage supply of the control and the power section.
• a generously dimensioned capacitor at the output helps to bridge short-term power withdrawals.
• FIGS. 4 and 5 show possible arrangements of the light-emitting diodes D.
• the arrangement according to FIG. 3, in which the individual diodes are arranged in matrix form, is particularly suitable for bright and dark field incident light or transmitted light.
• the arrangements according to FIGS. 4 and 5 are particularly suitable for rotationally symmetrical bright-field incident light. Both the arrangement and the number of segments and the number of light-emitting diodes per segment are variable within wide limits.
• the light-emitting diodes D of a "line" can each be combined to form a group which is controlled jointly.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Led Devices (AREA)
• Studio Devices (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=6404275

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Cited By (3)

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Citations (2)

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• 1990
  • 1990-04-12 DE DE4011842A patent/DE4011842A1/de active Granted
• 1991
  • 1991-04-12 WO PCT/DE1991/000305 patent/WO1991016786A1/de unknown

Patent Citations (2)

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