Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
  • G03B15/00—Special procedures for taking photographs; Apparatus therefor
  • G03B15/16—Special procedures for taking photographs; Apparatus therefor for photographing the track of moving objects
• • 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
  • H04N23/72—Combination of two or more compensation controls
• • 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
• • 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
  • H04N23/75—Circuitry for compensating brightness variation in the scene by influencing optical camera components
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/50—Control of the SSIS exposure
  • H04N25/53—Control of the integration time
  • H04N25/531—Control of the integration time by controlling rolling shutters in CMOS SSIS

Definitions

• the present invention relates generally to the generation of an electronic image and, more particularly, concerns the generation of an image of a moving object, making use of a rolling shutter.
• CMOS sensors Two well-known types of electronic image sensors are CMOS sensors and charge- coupled devices (CCDs).
• CCDs charge- coupled devices
• CMOS sensors generally, represent the lower cost option and have a number of other advantages.
• CMOS fabrication technologies lend themselves to the inclusion of timing circuits, analog-to-digital converters, and other functional blocks within an area of the image sensor.
• CCD sensors on the other hand, must be accompanied by separate circuits that provide those functions.
• CCD sensors have the advantage that they incorporate an electronic shutter mechanism known as a global shutter.
• imagers of this type the entire device is reset before integration (collection of light) to remove any residual signal in the sensor wells (pixel defining elements) of an imager.
• the pixels then accumulate charge for a predefined integration period, with light collection starting and ending simultaneously for all pixels.
• all charges are transferred simultaneously to light shielded areas of the sensor to prevent further accumulation of charge during the readout process.
• the charges are then shifted out of the light shielded areas of the sensor and read out.
• a global shutter sensor an image of a moving object is "frozen" in time, provided that the integration time is short enough to avoid motion blur. It is known that, with a global shutter, motion blur can be reduced or avoided by using a short duration flash of illumination, as when a flash photograph is taken.
• CMOS image sensors use a rolling shutter, which operates differently, in that the photodiodes (pixels) do not collect light at the same time. All pixels in one row of the imager collect light during exactly the same period of time, but the time light collection starts and ends is slightly different for each row. the top row of the imager being the first one to start collecting the light and the first one to finish collecting. The start and end of the light collection for following rows is slightly, although increasingly, delayed. The total light collection time for each row may be exactly the same; and the delay between rows may be constant.
• the time delay between a row being reset and a row being read is die integration time. By varying the amount of time between when the reset sweeps past a row and when the readout of the row takes place, the integration time can be controlled.
• CMOS imager One type of imaging apparatus which often utilizes a CMOS imager is a barcode reader. Scanning barcodes on objects on a moving conveyor belt can represent a particularly challenging task. Not only are the barcodes relatively small, but the code elements are very, closely spaced. The barcode must be imaged accurately for proper decoding, and image blur can impede that process. Even a relatively slowly moving barcode may therefore be the equivalent of a rapidly moving object, from the point of view of the quality of the image to be formed. It will be appreciated that the difficulty with barcodes is substantially increased when a two-dimensional barcode is utilized. It would be desirable to be able to image a moving barcode without resorting to the use of intense flashing light.
• a relatively rapidly moving object may be imaged with a sensor incorporating a rolling electronic shutter, while using flash illumination which is comparable to or dimmer than ambient light.
• flash illumination which is comparable to or dimmer than ambient light.
• the physical shutter is also operated so as to be open for a time interval which is coextensive with the presence of the flash.
• an optical mechanism may is the provided between the object and sensor which causes the image to be focused when the light is flashed and blurred otherwise.
• an optical filter is positioned between the object and sensor, and this filter is constructed to transmit to the CMOS sensor light at the wavelength of the flashing light source but to attenuate ambient light.
• the ambient light and flashing light source combine to provide sufficient power for imaging.
• the exposure time can be minimized.
• distortion and blur are minimized by having a small exposure time, but ambient light and a flashing light source combine to make the incident power enough to image the desired object.
• FIGS. l(A) and l (B) are timing charts illustrating the operation of a CMOS (rolling shutter) and a CCD (global shutter) imager, respectively;
• FIGS. 2(A) and 2(B) are timing charts illustrating the operation of a CMOS (rolling shutter) and a CCD (global shutter) imager, respectively, with flash illumination;
• CMOS rolling shutter
• CCD global shutter
• FIG. 3 is a timing chart illustrating the operation of a CMOS (rolling shutter) imager, with the addition of a physical shutter;
• FIG. 4 is a functional block diagram illustrating a first embodiment 30 of an imaging system embodying the present invention
• FIG. 5 is a functional block diagram illustrating a second embodiment 30' of an imaging system embodying the present invention.
• FIG. 6 is a functional block diagram illustrating a third embodiment 30" of an imaging system embodying the present invention.
• FIGS. l(A) and l(B) are timing charts illustrating the operation of a CMOS (rolling shutter) and a CCD (global shutter) imager, respectively.
• the imager has N lines, each containing a plurality of sensors.
• a CMOS sensor is represented simply as photodiodes PD, and a CCD sensor as a photodiode PD.
• the sensors are allowed to accept light energy, after being reset at 14, for an integration time T mU at the conclusion of which all gates are enabled simultaneously at 16, causing all the cells of the imager to be read out at the same time.
• every line stops accepting light at precisely the same instant, which has a stop action effect.
• the cells of line 0 begin receiving light energy at 10, and the entire line is read out at 12, after integration time Tim-
• each of the subsequent lines experiences an integration time Ti nt , but it does not start receiving light until a delay after the preceding line starts.
• Ti nt the integration time
• each line is captured after the object has experienced a certain amount of movement since the previous line.
• the CMOS imager exhibits a trapezoidal distortion, and image blur.
• an upright rectangular object takes on a trapezoidal shape tilt shape, making it seem to tilt away from the direction of movement, because the object has moved a little in between each line being imaged. This makes reading a two-dimensional barcode problematic.
• the image is blurred, because the object is moving during the imaging time.
• the blurring of the image is even more difficult to correct for.
• FIGS. 2(A) and 2(B) are timing charts illustrating the operation of a CMOS (rolling shutter) and a CCD (global shutter) imager, respectively, with flash illumination. It is well- known in photography that flash illumination can "stop motion", allowing fixed images of moving objects. Since all the cells in a CCD imager are read out simultaneously, using flash illumination is a natural extension. As can be seen in FIG. 2(B), it is only a matter of assuring that the cells receive sufficient illumination during Tj 1n .
• FIG. 2(A) is a timing chart illustrating the operation of a CMOS (rolling shutter) with addition of a physical shutter.
• a physical shutter (not necessarily mechanical, as illustrated), is synchronized to open at the start of the flash illumination, preferably at a time after the reset of the last line and before the readout of the first line, as shown at 20 in FIG. 3.
• the shutter is open for the entire duration of the flash. This permits the use of only the amount of illumination necessary to produce the required exposure, since each line also receives the same amount of ambient light, it receives the same amount of total exposure as every other line. As a result it becomes possible to use flash illumination which is comparable to or less than ambient light in intensity.
• One exemplary manner in which to implement the physical shutter is to use a rotating disk or similar member with apertures so that there is periodically an opening for the light to impinge upon the sensor.
• the flash illumination and the image sensor must be synchronized to capture the light reflected during the time that each opening of the physical shutter permits the passage of light.
• FIG. 4 is a functional block diagram illustrating a first embodiment 30 of an imaging system embodying the present invention.
• the system images an object O which is moving as indicated by the arrow A.
• Object O includes a code, such as a two-dimensional barcode, facing to right in FIG. 4, which is to be imaged on an imager or sensor array 32.
• imager 32 is a CMOS imager.
• the image is formed on imager 32 through a lens 34, and a physical shutter 36, such as an electronic or mechanical shutter, is interposed between lens 34 and object O.
• objects oh was illuminated by a flashing device 38, which provides the flashing illumination F.
• a controller 40 controls flashing device 38 and shutter 36 so that the shutter opens coincidentally with the initiation of the flash illumination F.
• controller 40 keeps shutter 36 open for the full duration of the flash illumination F. In this manner, the operation illustrated in FIG. 3 is achieved.
• FIG. 5 is a functional block diagram illustrating a second embodiment 30' of an imaging system embodying the present invention.
• System 30' is identical to system 30 of FIG. 4, except that lens 36 is replaced by an optical mechanism 36'.
• Mechanism 36' is controlled by controller 40 so as to focus the image of the object of O doing the flash F, but to provide a blurred focus in the absence of the flash F.
• mechanism 36' may, for example, be an electronically controllable liquid crystal lens.
• embodiment 30 prime achieves the operation illustrated in FIG. 3. It will be appreciated that both they shutter 36 and an adjustable focus mechanism 36' could be provided in the same system.
• FIG. 6 is a functional block diagram illustrating a third embodiment 30" of an imaging system embodying the present invention.
• shutter 36 or optical mechanism 36' is replaced by a lens 36".
• a flashing device 38" is utilized which provides light in a predetermined frequency that is substantially different from ambient light.
• Lens 36" is constructed so as to transmit the frequency of the flashing device 38' and to block the frequencies contained in ambient light. As a result, imager 32 will receive only the image illuminated by flashing a light F.
• the effective integration time can thus be set by changing the pulse width of the incident light, when the flash is used, or by changing the electronic shutter period of the sensor array.
• the system designer may choose either, or the system may include a light sensor that chooses which manner in which to control the effective integration time of the CMOS or other sensor, depending upon whether the ambient light is beyond a predetermined threshold or not.

Landscapes

• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Studio Devices (AREA)
• Transforming Light Signals Into Electric Signals (AREA)
• Exposure Control For Cameras (AREA)
• Stroboscope Apparatuses (AREA)
• Blocking Light For Cameras (AREA)
• Automatic Focus Adjustment (AREA)
• Shutters For Cameras (AREA)
• Testing Of Coins (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

Family

ID=39875758

Family Applications (1)

Country Status (4)

Cited By (1)

Families Citing this family (18)

Citations (1)

Family Cites Families (9)

• 2007
  • 2007-04-18 JP JP2010504025A patent/JP2010527457A/ja active Pending
  • 2007-04-18 DE DE112007003452T patent/DE112007003452T5/de not_active Withdrawn
  • 2007-04-18 US US12/596,528 patent/US20100329657A1/en not_active Abandoned
  • 2007-04-18 WO PCT/US2007/009421 patent/WO2008130343A1/en not_active Ceased

Patent Citations (1)

Also Published As

Similar Documents

Legal Events