Determination procedure of the luminance of traffic signs and device for its embodiment

Abstract

The method of the invention comprises: obtaining a sequence of at least two images, with different levels of illumination; extracting the region containing the sign in the image; calculating the luminance values of the signs; and obtaining the difference in luminance of the sign corresponding to the two levels of illumination. The value obtained is the luminance of the sign (11) corresponding to an illumination equal to the difference between the illuminations, or additional illumination. This result is based on the additive property of luminance, according to which the luminance of a sign is the sum of the luminance produced by each source of illumination. A basic illumination device (5), an additional illumination device (7), at least one camera for taking images, and image recording, positioning and synchronism systems are required to implement the method.

Claims

1. Determination procedure of the luminance of traffic signs characterized in that it comprises the following stages: a) Obtaining a sequence of images composed of at least two images with different illumination levels. b) Extracting the region where the sign is on the image. c) Calculating the luminance values of the signs. d) Obtaining the difference in luminance of the sign corresponding to the two illumination levels.

2. Determination procedure of the luminance of traffic signs in accordance with claim 1, characterized in that the capturing of the two images with different illumination levels is done with an interval of time
Δt=p/(2*n*f) where “f” is the supply frequency of the public lighting network and “n” and “p” are whole numbers.

3. Device for the determination of the luminance of traffic signs which, using the procedure of the above claims, is characterized by comprising the following, fitted on a vehicle: at least one camera for capturing the images, a base illumination device, an additional illumination device, a positioning system, a system for image and data recording and treatment, a synchronism system.

4. Device for the determination of the luminance of traffic signs in accordance with claim 3, characterized in that the cameras for capturing images are digital cameras.

5. Device for the determination of the luminance of traffic signs in accordance with claim 3, characterized in that the base illumination device (5) comprises the dipped lights of the vehicle with a stabilizer system (6).

6. Device for the determination of the luminance of traffic signs in accordance with claim 3, characterized in that the additional illumination device (7) comprises external lamps and an adjustment and control device (8) working in a closed loop which by means of some sensors (9) for the light intensity maintains a constant illumination level C modifiable by an operator.

7. Device for the determination of the luminance of traffic signs in accordance with claim 3, characterized in that the positioning system comprises a GPS device.

8. Device for the determination of the luminance of traffic signs in accordance with claim 3, characterized in that the image and data recording system comprises; a digital storage device, a device that applies some transformation equations enabling the luminance of each pixel to be obtained from its characteristic values.

9. Device for the determination of the luminance of traffic signs in accordance with claim 3, characterized in that the synchronism system comprises a local positioning device via the milometer of a vehicle on which it is installed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] To complement the foregoing description, and with the aim of aiding a better understanding of the characteristics of the invention, a detailed description of a preferred embodiment is going to be made, on the basis of a set of plans accompanying this descriptive specification in which, on an orientative rather than limiting basis, the following has been represented.

[0056] FIG. 1 shows a vehicle fitted with the device of the invention, approaching a traffic sign.

[0057] FIG. 2 shows the front of the above vehicle with the additional and base illumination devices.

[0058] FIG. 3 shows the vehicle with the base illumination and additional illumination switched on.

[0059] FIG. 4 shows the vehicle with just the base illumination switched on.

[0060] FIG. 5 shows, schematically in time, the determination of the luminance of two traffic signs.

[0061] In the above figures, the numerical references correspond to the following parts and elements. [0062] 1. Driver. [0063] 2. Sign panel. [0064] 3. Distance between the driver and the sign. [0065] 4. Normal to the sign panel 2. [0066] 5. Base illumination. [0067] 6. Stabilizer for the base illumination. [0068] 7. Additional Illumination. [0069] 8. Adjustment and control of the additional illumination. [0070] 9. Light intensity sensor. [0071] 10. Public lighting. [0072] 11. Vertical traffic sign.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0073] As can be seen in FIG. 1, a driver (1), as he goes along the road, perceives the information shown in the different signing elements. For a sign panel (2) lying within the angle of vision of the driver (1), at a distance (3) and in a defined instant, an angle of entrance 13 is defined formed between the light beam incident on the luminous surface at a point and normal (4) to that surface at that point, and also an angle of observation a formed by the light beam incident on the surface and the reflected light reaching the eyes of the driver (1). As the driver approaches the sign these angles change and the luminance perceived by the observer varies.

[0074] The luminance provided by a sign, especially if it consists of a back-reflecting material, depends on various factors: [0075] Contributed light. In case of internally lit signs, the reflected light is independent of the contributed light, but for back-reflecting materials, the greater the amount of light that is contributed to the sign, the more light that is reflected. [0076] Angle of entrance 13 and of observation a. [0077] Special properties of the material. In particular the variation in back-reflection with the angle of visualization with respect to the normal. [0078] The rotation of the sign about its axes (angles of twist, roll and dip).

[0079] In order to calculate the distance of the vehicle from the sign, a technique will be used based on the analysis of the images, using a single camera, though it can be extended to an array of cameras or specific techniques of triangulation or stereovision can be used. The procedure used in the present embodiment starts from the analysis of the image by known techniques of artificial vision which permits the position of an object of interest to be determined on that image on the basis of the size of that object as it appears in the image. Applied to different images of the same object, whose cadence is known thanks to the synchronism system, it is possible to establish a direct relation between the real size of the sign, the size of the sign in the image and the distance to the sign. Taking samples of the sizes of the object in the image, as well as the relative distances of the different images to one chosen as reference, it is possible to generate a set of geometric transformation equations on the basis of which the distance that is sought and the size of the object can be determined.

[0080] In order to carry out the procedure of the invention for determination of the luminance, a device is used which, fitted to a vehicle, comprises at least: [0081] One camera for capturing the images. [0082] A base illumination device. [0083] An additional illumination device. [0084] A positioning system. [0085] A system for image and data recording and treatment. [0086] A synchronism system.

Cameras

[0087] The aim of the present invention is to study the luminance perceived by the driver. For this reason, the location has been considered of at least one of the cameras in a suitable position on the vehicle that is close to the eye of the driver.

[0088] Digital cameras permit the colour coordinates of objects to be represented in an image defined by a set of pixels.

[0089] The representation of the colour is normally done by means of the coordinates R, G, B (Red, Green, Blue) though there exist other systems, for example in 1931 the International Commission on Illumination established the system XYZ or CIE 1931. In it, the Y component represents the energy or luminance of the pixel and X and Z the colour. For standard camera systems (PAL, NTSC) many different combinations have been defined for transforming the RGB system to XYZ, as in the case of standard ITU.BT-601. In this way, in order to obtain the luminance of an object, it will suffice to carry out the transformation between the systems and determine the value of Y.

[0090] In the system used in this embodiment, and depending on the camera, a conversion will be applied like that described above (standard) or a non-standard transformation that comprises the following steps: [0091] A standard illuminant is selected defined by the CIE. [0092] A white balance is carried out (see document “Digital Color Imaging Handbook”. Gaurav Sharma, ed. CRC PRESS, Boca Raton, New York, Washington, D.C.). [0093] Using a colour card according to the CIE 1931 standard, obtain the colour coordinates of pure red, green and blue with the camera. [0094] Using a colour card, obtain the XYZ colour coordinates of pure red, green and blue with a colorimeter as per standard CIE 1931. [0095] Obtain the conversion coefficients for colour to grey level starting from both measurements.

[0096] The vehicle has two illumination systems, one which corresponds to the base illumination and the other which corresponds to the additional illumination. These two systems have to be adapted in order to permit a reliable measurement. See FIG. 2.

Base Illumination Device

[0097] In a preferred embodiment the base illumination (5) consists of the dipped lights of the vehicle, powered by the battery, whose voltage oscillates depending on its state of charge, its degree of aging, etc. Given that the illumination provided by these lights is directly related to the battery voltage, a stabilizer (6) needs to be inserted to compensate for the oscillations in that voltage.

Additional Illumination Device

[0098] In a preferred embodiment, the additional illumination (7) consists of the lamps external to the vehicle, which have to meet the following requisites: [0099] They must provide a constant level of illumination during the data gathering, independently of oscillations in the supply voltage, of the temperature of the bulbs of the external lamps, and of the wear undergone by those lamps with time. [0100] They have to provide a known level of illumination at each moment. [0101] The level of illumination has to be able to be adjustable for each specific period of data gathering.

[0102] On account of all this, an adjustment control system (8) is needed for the additional illumination in a closed loop that can take on these responsibilities. Basically, the functioning of this system can be summarized as: [0103] It measures the illumination by means of a sensor (9). [0104] It compares it with a desired level C, modifiable by the operator. [0105] It takes the decisions in the various control elements.

[0106] The map of intensity of the light provided by the additional lamps is known and controlled. Their light intensity is adjusted in such a way that avoids disturbing other circulating vehicles, preventing dangerous situations from arising that can be created by the other patents commented on above.

[0107] The additional lamps have to have a short response time. This can be achieved by means of lamps that are sufficiently fast (for example, based on LEDs) or with mechanical shutter systems that permit a sudden and controlled variation in the illumination that its provided.

[0108] The level of intensity of the illumination provided by the lamps has to be controlled and its geometric distribution has to be known.

[0109] The system described in the present embodiment permits data gathering to be done in movement along the road. In order to avoid disturbing other users traveling on the same road, it is necessary to follow the instructions regarding the design of lamps and maximum illumination levels for each emitter-observer angle that can be admissible, such as for example those defined in Regulation N° 8 of the United Nations Economic Commission for Europe.

Image and Data Recording and Treatment System

[0110] The system comprises: [0111] A digital storage device. [0112] A device that applies some transformation equations enabling the luminance of each pixel to be obtained starting from its characteristic values (grey scale).

Positioning System

[0113] The system comprises: [0114] A geo-referenced positioning device (GPS) and its corresponding antenna. [0115] An information recording device.

Synchronism System

[0116] The system comprises a local positioning device (via the vehicle's milometer) which provides the distance traveled, and a device that generates certain events as a function of that distance traveled. The synchronism system allows adjustment of the distance from the start to when the images are captured and the delay time between each of them.

[0117] The synchronism system has to be such that permits adjustment of the on and off times of the lamps with sufficient precision for eliminating the subcyclic effects of public lighting. If f is the frequency of the grid (normally 50 Hz in Europe) the subcyclic effects have a duration of 1/(2*n*f) n=1 . . . N. On the other hand, given that the described device is capable of capturing images while moving, the duration of the time for capturing each image will be sufficiently small so as not to alter the size of the objects appearing in them and it will also be a multiple of the subcyclic frequencies. The interval of time between capturing two successive images of the same sign with variation in the illumination will be;

Δt=p/(2*n*f) with n=1 . . . N and p=1 . . . P.

[0118] In this way, as “n” and “p” are whole numbers, the moment of capturing each image will occur at the same point of the wave of the supply voltage from the electric grid, thus minimizing the differences in the uncontrolled ambient illumination.

[0119] The general operating procedure is as follows. A vehicle fitted with the devices and systems described above can circulate on the road and record different sequences of images of various signs situated along that road. With a view to a better understanding vertical signs will, for example, be used, though the procedure of the present invention is valid for any kind of sign that is the object of study.

[0120] As the vehicle approaches the sign (11), the sign will be seen to become displaced in the image and its size will increase until it disappears from the field visible to the camera.

[0121] The method that allows the effects of external illumination, such as public lighting (10) for example, to be cancelled out consists of capturing images with different illumination levels, by a combination of base illumination (5) and the additional illumination (7) of the vehicle, obtaining the value of the differential luminance, which cancels out the effect of the ambient illumination as well as the base illumination of the vehicle.

[0122] As can be seen in FIG. 3, first of all the images are captured with the base illumination (5) and the additional illumination (7) switched on. Then, with an interval of time determined by the synchronism device, the additional illumination (7) is switched off or hidden in order to obtain the second image as can be seen in FIG. 4.

[0123] The synchronism system establishes the instants of time in which the two images are captured corresponding to two illumination levels L1 and L2. See FIG. 5.

[0124] Finally, the location data is stored, along with the time of the synchronism system.

[0125] Once the data has been downloaded, an automatic computer programme processes the images where the vertical signs (11) appear and it extracts the region corresponding to that sign. Another automatic procedure calculates the luminance level on the basis of a grey scale. Finally, the differential luminance is obtained from L1 and L2.

[0126] The relation with the positioning system allows the relative position of the image and the sign on the road to be calculated.

[0127] It will be evident to an expert in the subject that, without departing from the essence of the invention, there is a series of modifications and variants that can be made allowing it to be adapted to the desired operating conditions. So, the additional illumination system has been described as an external light incorporated into the vehicle, but it could be included among the vehicle's own lamps with suitable control. No details have been given of those processes and devices which, being conventional, will be more than familiar to the expert in the subject.