GB2419761A - Control of settings for a vehicle registration plate recognition imaging system - Google Patents

Control of settings for a vehicle registration plate recognition imaging system Download PDF

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Publication number
GB2419761A
GB2419761A GB0424192A GB0424192A GB2419761A GB 2419761 A GB2419761 A GB 2419761A GB 0424192 A GB0424192 A GB 0424192A GB 0424192 A GB0424192 A GB 0424192A GB 2419761 A GB2419761 A GB 2419761A
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GB
United Kingdom
Prior art keywords
interest
settings
image capture
capture device
properties
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB0424192A
Other versions
GB0424192D0 (en
Inventor
Lawson John Noble
Frank James Thomson
Nico Bekooy
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Tagmaster UK Ltd
Original Assignee
Citysync Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Citysync Ltd filed Critical Citysync Ltd
Priority to GB0424192A priority Critical patent/GB2419761A/en
Publication of GB0424192D0 publication Critical patent/GB0424192D0/en
Publication of GB2419761A publication Critical patent/GB2419761A/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G08—SIGNALLING
    • G08G—TRAFFIC CONTROL SYSTEMS
    • G08G1/00—Traffic control systems for road vehicles
    • G08G1/01—Detecting movement of traffic to be counted or controlled
    • G08G1/017—Detecting movement of traffic to be counted or controlled identifying vehicles
    • G08G1/0175—Detecting movement of traffic to be counted or controlled identifying vehicles by photographing vehicles, e.g. when violating traffic rules
    • 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
    • H04N23/72—Combination of two or more compensation controls
    • H04N5/2352—

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Studio Devices (AREA)
  • Image Input (AREA)

Abstract

A method and system for controlling an image capture device 3 comprises the steps of applying first settings to the device 3, capturing an image containing an object of interest, preferably a vehicle registration plate (7, fig. 2), and analysing properties of the object (7, fig. 2), preferably including brightness or the contrast between two regions of the object. Second settings are then applied to the device 3 in response to the analysed properties, preferably including: the diameter of the device's iris; brightness and/or pulse frequency of illumination means 4; gain and/or contrast applied to the images captured and; shutter speed. Preferably the method can further comprise the steps of capturing a number of images including an object of interest, analysing each of the images and applying settings to the device 3 in response to a combination of the properties, preferably their average.

Description

"A Method of Controlling the Settings of an Image Capture Device" THIS
NVENTION relates to a method of controlling the settings of an image capture device, and an image capture system employing the method. In particular, the invention relates to a system and method for controlling the settings of an image capture device to allow an object of interest to be imaged effectively in various lighting conditions.
There are many situations in which an image capture device, for instance a CCD camera, may be placed in a fixed location for a considerable length of time, in order to capture multiple images of objects passing through the field of view of the image capture device. An example of such a situation is an image capture device placed by a roadside, on a bridge over a road or near the entrance to a car park, in order to capture images of registration plates of vehicles passing through the field of view of the image capture device.
In such a situation, the ability of the image capture device to capture a useful image of a vehicle registration plate is dependent upon the lighting conditions applied to the registration plate, as well as the settings applied to the image capture device. Such settings may include the iris diameter and shutter speed of the image capture device, the gain or brightness applied to images captured thereby, and the intensity and pulse frequency of artificial lighting illuminating the registration plate. Settings that may be appropriate during bright sunlight may be inadequate during darkness, and settings that may be appropriate during darkness (e.g. including intense artificial illumination) may be wasteful of energy during daylight.
It has been proposed to vary the settings applied to an image capture device in response to the brightness of a captured image. However, this technique suffers from drawbacks, in that vehicle registration plates often react to illumination conditions in a different manner to most background objects, due to the reflectivity thereof and the contrast between the background of the registration plate and the characters displayed thereon. Hence, the brightness of a captured image may not provide sufficient information to vary the settings applied to an image capture device in order to capture useful images of vehicle registration plates.
It is an object of the present invention to seek to alleviate the above difficulties.
Accordingly, one aspect of the present invention provides a method of controlling settings of an image capture device, comprising the steps of: applying first settings to an image capture device; capturing an image, the image comprising an object of interest and a background; analysing properties only of the object of interest; and applying second settings to the image capture device in response to the analysed properties of the object of interest.
Advantageously, the analysed properties include the brightness of the object of interest, and the settings include the diameter of an iris of the image capture device.
Preferably, the analysed properties include the brightness of the object of interest, and the settings include the brightness of illumination applied to the object of interest.
Conveniently, the analysed properties include the brightness of the object of interest, and the settings include a pulse frequency of illumination applied to the object of interest.
Advantageously, the analysed properties include the brightness of the object of interest, and the settings include a gain applied to images captured by the image capture device.
Preferably, the analysed properties include the brightness of the object of interest, and the settings include a shutter speed of the image capture device.
Conveniently, the analysed properties include contrast between two regions of the object of interest, and the settings include the contrast applied to images captured by the image capture device.
Advantageously, the method further comprises the steps of: capturing a number of images, each comprising an object of interest and a background; analysing properties only of the object of interest in each of the captured images; and applying the second settings to the image capture device in response to a combination of the analysed properties from the captured images.
Preferably, the combination of the analysed properties comprises an average of the analysed properties.
Conveniently, the second settings are applied in response to the analysed properties of the object of interest only.
Another aspect of the present invention provides an image capture system operable to: configure an image capture device in accordance with first settings; capture a first image, the image comprising an object of interest and a background; analyse properties only of the object of interest; and configure the image capture device in accordance with second settings, the second settings being selected in response to the analysed properties of the object of interest.
Conveniently, the analysed properties include the brightness of the object of interest, and the settings include the diameter of an iris of the image capture device.
Advantageously, the analysed properties include the brightness of the object of interest, and the settings include the brightness of illumination applied to the object of interest.
Preferably, the analysed properties include the brightness of the object of interest, and the settings include a pulse frequency of illumination applied to the object of interest.
Conveniently, the analysed properties include the brightness of the object of interest, and the settings include a gain applied to images captured by the image capture device.
Advantageously, the analysed properties include the brightness of the object of interest, and the settings include a shutter speed of the image capture device.
Preferably, the analysed properties include contrast between two regions of the object of interest, and the settings include the contrast applied to images captured by the image capture device.
Conveniently, the system is operable to: capture a number of images, each comprising a foreground object of interest; analyse properties only of the object of interest in each of the captured images; and configure the image capture device in accordance with the second settings, the second settings being selected in response to a combination of the analysed properties from the captured images.
Advantageously, the combination of the analysed properties comprises an average of the analysed properties.
In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an image capture system embodying the present invention; and Figure 2 shows an image of the type that may be captured by the system of Figure 1.
With reference firstly to Figure 1, an image capture system 1 embodying the present invention is shown. The image capture system 1 is positioned at an entrance 2 to, for example, a car park. The image capture system 1 comprises an image capture device 3, which may be, for example, a CCD camera or other device capable of capturing a storable image. The image capture device 3 is positioned such that its field of view covers a predetermined target location.
The image capture system 1 further comprises two illumination devices 4, which may comprise banks of LEDs. The illumination devices 4 are advantageously configured such that illumination emitted thereby is strongly reflected by a typical vehicle registration plate. In preferred embodiments of the invention the illumination output by the illumination devices is pulsed at a variable pulse frequency, thus providing a further means of altering the intensity of illumination output thereby.
The illumination devices are also positioned such that illumination emitted thereby is directed towards the target location.
The image capture system 1 is positioned in a suitable location such that vehicles 5 entering the car park will pass through the target location. The image capture system 1 detects the presence of a vehicle 5, either by the presence of a vehicle 5 in the field of view of the image capture device 3 or by alternative sensing means. The image capture system 1 then captures an image of the vehicle using the image capture device 3. While this image is captured, the vehicle may be illuminated by the illumination devices 4.
While this image is captured, first settings are applied to the image capture system 1. These settings may include, but are not limited to, the diameter of an iris of the image capture device 3, the shutter speed of the image capture device 3, the gain control, brightness or contrast applied to images captured by the image capture device 3, and the intensity and pulse frequency of the illumination provided by the illumination devices 4. It will be appreciated that each of these parameters will influence the quality of the captured image, and in particular the ease with which characters on the registration plate of a vehicle in the captured image can be distinguished.
A processor (not shown) of the image capture device 1 then processes the captured image (an example of the type of image that might be captured is shown in Figure 2) using suitable image processing software. Firstly, the captured image 6 is analysed to identify the registration plate of the vehicle 5.
Techniques employed to recognise a vehicle registration plate, the object of interest, within a captured image and separate that from the remainder of the image, the background are known, and will not be discussed in great detail in this specification. However, a captured image is analysed to search for rectangles of appropriate size and shape in the complete image, and various criteria are employed to filter out background which is non-rectangular and rectangular features which do not comprise the registration plate. Ultimately the system arrives at a decision as to which object in the captured image is most likely to be the registration plate - the object of interest.
Once the image processing software has determined which region 7 of the captured image comprises the registration plate of the vehicle 5, character recognition routines are applied to this region 7 to read the characters displayed on the registration plate. This information may be transmitted to a remote location for storage, comparison against a database of stolen vehicles, and so forth.
However, the region 7 of the captured image is also analysed to determine certain properties thereof. Preferably, these properties include the brightness of the region 7 of the captured image 6, and also the contrast between the characters which appear in the region 7 of the captured image 6
and the background thereof.
It will be appreciated that, for the purposes of character recognition, there are desirable brightness and contrast characteristics of a captured image.
The image processing software compares the measured brightness and contrast of the region 7 of the captured image 6 with the desired brightness and contrast levels for character recognition.
If it is discovered that the measured brightness and contrast levels differ from the desired levels, the processor alters the settings of the image capture device 1 in an attempt to ensure that a next captured image will be more suited to character recognition.
For instance, if the region 7 of the captured image 6 is too bright, and the illumination devices 4 were used to illuminate the vehicle when the image 6 in question was captured, the processor may reduce the intensity of the illumination emitted by the illumination devices 4, may reduce the frequency of the illumination emitted by the illumination devices 4, or alternatively may de- activate the illumination devices 4 entirely. Which of these is selected, and the amount by which the intensity and/or pulse frequency of the illumination are reduced, depends upon the measured brightness of the region 7 of the captured image 6. It will be understood that the de- activation of the illumination devices i.e. when not required, will also help to reduce the power consumption of the system 1.
Alternatively, if the measured brightness of the region 7 of the captured image 6 is too low, the processor may activate the illumination devices 4, or may increase the intensity and/or pulse frequency of the illumination emitted thereby.
Alternatively, or in addition, the shutter speed or iris diameter of the image capture device 3, or the gain control applied to images captured by the image capture device 3 may be varied in response to the measured brightness of the region 7 of the captured image 6, and a skilled person will understand how these variations may be effected to influence the brightness of a registration plate of a vehicle in a subsequently captured image.
The contrast between the characters on the registration plate and the background of the registration plate is also measured. If the contrast is too high or too low, the contrast applied to images captured by the image capture device 3 may be altered to improve the quality of subsequently captured images for the purposes of character recognition, and again a skilled person will readily appreciate how this may be achieved.
It should be noted that it is the region 7 of the captured image 6 which is determined to comprise the number plate, the object of interest, and no other region of the captured image 6, that is analysed for the purposes of adjusting the settings of the image capture system 1. Other regions of the vehicle 5 and background objects are not taken into account for these purposes. This ensures that, while lighting conditions suitable for character recognition on a registration plate may be very different from those required for effectively viewing the remainder of the vehicle or background objects, the settings of the image capture system 1 are varied solely to ensure that characters displayed on vehicle registration plates may be read effectively.
In advantageous embodiments of the invention, the image capture system 1 may capture a number of images, for instance ten successive images, and adjust the settings of the image capture system 1 based upon a combination of the measured properties of vehicle registration plates appearing in the series of captured images. For instance, the settings of the image capture system 1 may be varied in accordance with an average of the measured brightnesses of the vehicle registration plates in the series of images.
The settings of the image capture system 1 may be altered, for instance, after each tenth captured image, or alternatively may be altered after every captured image, on the basis of the immediately preceding ten captured images.
These embodiments reduce the likelihood of the settings of the image capture system 1 being altered disadvantageously in response to transient conditions, such as a brief but isolated period of bright sunlight, or strong light shining on the target location from an external source.
In other advantageous embodiments of the invention, a number of images may be captured, with the settings applied to the image capture system 1 for a given image being in response to the conditions under which the immediately proceeding image was captured. Therefore, whilst an object of interest is within the field of view, a plurality of images may be taken. Should a considerable amount of time pass between objects of interest passing through the field of view (for example 12 hours - thus changing from daytime to night time), then it is likely that the settings applied to the image capture device 1 when the first image of the second object of interest is captured would be completely inappropriate. However, advantageous embodiments of the invention allow a plurality of images to be captured, the analysed properties of each image serving as a basis for the settings applied to each subsequent image.
Therefore, in the example given above, the second image taken of the second object of interest is likely to be much more suitable - since the settings of the cg image capture device are based on the analysed properties of the first image of the second object of interest.
It will be appreciated that in order to improve the likelihood of a suitable image being captured, both the averaging method and the method based on the immediately proceeding image can be used.
Still further, it is envisaged that the settings applied to the image capture device 1 when capturing an image can be in response to the analysed properties of an image taken by the image capture device 1 at a time when the ambient conditions are similar to those under which the current image is being captured.
Thus, the settings applied to the image capture device 1 when capturing an image at, for example, 6pm, can be in response to the ambient conditions sensed at 6pm the previous day (or an average of sensed conditions over a plurality of days).
It will be appreciated that the present invention provides a flexible method and system for ensuring that images captured by an image capture device will be useful for character recognition purposes under varying illumination conditions.
In the present specification "comprises" means "includes or consists of' and "comprising" means "including or consisting of'.
The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (22)

  1. CLAIMS: 1. A method of controlling settings of an image capture device,
    comprising the steps of: applying first settings to an image capture device; capturing an image, the image comprising an object of interest and a
    background;
    analysing properties only of the object of interest; and applying second settings to the image capture device in response to the analysed properties of the object of interest.
  2. 2. A method according to Claim 1, wherein the analysed properties include the brightness of the object of interest, and the settings include the diameter of an iris of the image capture device.
  3. 3. A method according to Claim 1 or 2, wherein the analysed properties include the brightness of the object of interest, and the settings include the brightness of illumination applied to the object of interest.
  4. 4. A method according to any preceding claim, wherein the analysed properties include the brightness of the object of interest, and the settings include a pulse frequency of illumination applied to the object of interest.
  5. 5. A method according to any preceding claim, wherein the analysed properties include the brightness of the object of interest, and the settings include a gain applied to images captured by the image capture device.
  6. 6. A method according to any preceding claim, wherein the analysed properties include the brightness of the object of interest, and the settings include a shutter speed of the image capture device.
  7. 7. A method according to any preceding claim, wherein the analysed properties include contrast between two regions of the object of interest, and the settings include the contrast applied to images captured by the image capture device.
  8. 8. A method according to any preceding claim, further comprising the steps of: capturing a number of images, each comprising an object of interest and
    a background;
    analysing properties only of the object of interest in each of the captured images; and applying the second settings to the image capture device in response to a combination of the analysed properties from the captured images.
  9. 9. A method according to Claim 8, wherein the combination of the analysed properties comprises an average of the analysed properties.
  10. 10. A method according to any proceeding claim, wherein the second settings are applied in response to the analysed properties of the object of interest only.
  11. 11. An image capture system operable to: configure an image capture device in accordance with first settings; capture a first image, the image comprising an object of interest and a
    background;
    analyse properties only of the object of interest; and configure the image capture device in accordance with second settings, the second settings being selected in response to the analysed properties of the object of interest.
  12. 12. A system according to Claim 11, wherein the analysed properties include the brightness of the object of interest, and the settings include the diameter of an iris of the image capture device.
  13. 13. A system according to Claim 11 or 12, wherein the analysed properties include the brightness of the object of interest, and the settings include the brightness of illumination applied to the object of interest.
  14. 14. A system according to any one of Claims 11 to 13, wherein the analysed properties include the brightness of the object of interest, and the settings include a pulse frequency of illumination applied to the object of interest.
  15. 15. A system according to any one of Claims 11 to 14, wherein the analysed properties include the brightness of the object of interest, and the settings include a gain applied to images captured by the image capture device.
  16. 16. A system according to any one of Claims 11 to 15, wherein the analysed properties include the brightness of the object of interest, and the settings include a shutter speed of the image capture device.
  17. 17. A system according to any one of Claims 11 to 16, wherein the analysed properties include contrast between two regions of the object of interest, and the settings include the contrast applied to images captured by the image capture device.
  18. 18. A system according to any one of Claims 11 to 17, operable to: capture a number of images, each comprising a foreground object of interest; analyse properties only of the object of interest in each of the captured images; and configure the image capture device in accordance with the second settings, the second settings being selected in response to a combination of the analysed properties from the captured images.
  19. 19. A system according to Claim 18, wherein the combination of the analysed properties comprises an average of the analysed properties.
  20. 20. A method substantially as hereinbefore described, with reference to the accompanying drawings.
  21. 21. A system substantially as hereinbefore described, with reference to the accompanying drawings.
  22. 22. Any novel feature or combination of features disclosed herein.
GB0424192A 2004-11-01 2004-11-01 Control of settings for a vehicle registration plate recognition imaging system Withdrawn GB2419761A (en)

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Application Number Priority Date Filing Date Title
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Application Number Priority Date Filing Date Title
GB0424192A GB2419761A (en) 2004-11-01 2004-11-01 Control of settings for a vehicle registration plate recognition imaging system

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GB2419761A true GB2419761A (en) 2006-05-03

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012010838A1 (en) * 2010-07-20 2012-01-26 Telematics Technology Llp Indicia identifying system
CN102629988A (en) * 2012-03-31 2012-08-08 博康智能网络科技股份有限公司 Automatic control method and device of camera head
CN111355900A (en) * 2020-03-12 2020-06-30 浙江大华技术股份有限公司 Image processing method and device, storage medium and electronic device

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0271386A (en) * 1988-09-07 1990-03-09 Mitsubishi Electric Corp Number plate recognizing device
EP0409161A2 (en) * 1989-07-18 1991-01-23 Fuji Photo Film Co., Ltd. Method and apparatus for controlling exposure changes of a video camera
JPH08287390A (en) * 1995-04-14 1996-11-01 Amano Corp Automatically recognizing method for number plate and device therefor
US5915032A (en) * 1989-08-22 1999-06-22 Minnesota Mining And Manufacturing Company Method and apparatus for machine reading of retroreflective vehicle identification articles
JP2001222680A (en) * 2000-02-08 2001-08-17 Mitsubishi Electric Corp License plate number reader

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0271386A (en) * 1988-09-07 1990-03-09 Mitsubishi Electric Corp Number plate recognizing device
EP0409161A2 (en) * 1989-07-18 1991-01-23 Fuji Photo Film Co., Ltd. Method and apparatus for controlling exposure changes of a video camera
US5915032A (en) * 1989-08-22 1999-06-22 Minnesota Mining And Manufacturing Company Method and apparatus for machine reading of retroreflective vehicle identification articles
JPH08287390A (en) * 1995-04-14 1996-11-01 Amano Corp Automatically recognizing method for number plate and device therefor
JP2001222680A (en) * 2000-02-08 2001-08-17 Mitsubishi Electric Corp License plate number reader

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012010838A1 (en) * 2010-07-20 2012-01-26 Telematics Technology Llp Indicia identifying system
GB2482243B (en) * 2010-07-20 2017-08-23 Ca Traffic Ltd Indicia identifying system
CN102629988A (en) * 2012-03-31 2012-08-08 博康智能网络科技股份有限公司 Automatic control method and device of camera head
CN111355900A (en) * 2020-03-12 2020-06-30 浙江大华技术股份有限公司 Image processing method and device, storage medium and electronic device

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