Abstract:
The invention refers to a digital camera  1  which can be used in a motion sensor  4.  In order to be able to test the function of the camera, a light source  3  is provided which irradiates at least a part of the sensing matrix  2.  The processor device  5  of the camera judges whether the output signal of the sensing matrix  2  corresponds correctly to the light which has irradiated the sensing matrix  2.  Various test methods are disclosed, such as using varying wavelengths, ON/OFF-modulation, dependence on shutter time and illumination of various regions of the sensing matrix  2.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Applicants claim priority under 35 U.S.C. §119 of German Application No. 10 2009 018 095.8 filed Apr. 20, 2009. 
       BACKGROUND OF THE INVENTION 
       [0002]    Motion sensors, for example motions sensors for door opening, of the prior art mostly work with Doppler-Radar. In other words, when an object or person approaches the sensor, a radar beam emitted from the sensor will be reflected by the object or person and the reflected beam will experience a frequency shift (Doppler-Effect). The reflected radiation will be recognized by the motion sensor. However, objects which move very slowly cannot be detected due to too low or non-existent Doppler-Effect. 
         [0003]    Using a camera in motion sensors provides better results, especially when slowly moving or still objects should be detected. However, cameras can fail due to defects in their recognition system. 
       SUMMARY OF THE INVENTION 
       [0004]    It is therefore an object of the present invention to provide a digital camera which can be easily and reliably tested as to its proper function. 
         [0005]    It is also an object of the present invention to provide a test method for testing the function of a digital camera which may be part of a motion sensor device. 
         [0006]    The above-mentioned objects are achieved by a digital camera and a method as claimed in the independent claims. 
         [0007]    Advantageous embodiments are the subject matter of the dependent claims. 
         [0008]    According to particular advantageous embodiments the digital camera comprises a processor device which is adapted to read out signals from the sensing element and analyses whether the read out signals correspond correctly to the electromagnetic radiation which is irradiated onto the sensing element by the radiation source. The radiation source, which may be a light source, may comprise several light elements, such as LEDs, which can be controlled individually. The light elements may be selected to emit different wavelengths and/or different intensities. Also an on/off-modulation may be provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention. 
           [0010]    In the drawing, 
           [0011]    The sole FIGURE shows schematically a motion sensor device which includes a digital video camera according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0012]    Referring now in detail to the drawing, a motion sensor device is shown, which includes a video camera  1  according to the invention. The digital video camera  1  comprises a sensing element  2  which has a square array or matrix of pixels. In front of the sensing element  2  there is shutter  6  which can be opened or closed. In the open status of the shutter light can travel from the camera lens  8  to the sensing element  2 . In the closed status of the shutter the light passage from the camera lens  8  to the shutter  6  is obstructed, i.e. no light from outside the camera can fall onto the sensing element  2 . The digital video camera  1  further comprises a processor device  5  which receives data from the sensing element  2 . An amplifier  7  with variable gain is provided which receives the pixel data from the sensing element  2  and outputs the data to the processor device  5 . The processor device  5  is connected to an evaluation station  9 . The processor device  5  is also connected to the gain control input of the amplifier  7 . Further, the processor device  5  is connected to the trigger input of the shutter  6 . 
         [0013]    Radiation sources  3 ,  3 ′ are provided between the optical camera lens  8  and the shutter  6 . Each of the radiation sources  3 ,  3 ′ comprises radiation elements  3   a,    3   b  and  3   c,    3   d,  respectively. In this example the radiation elements are light emitting diodes (LED). The radiation sources  3 ,  3 ′ are arranged in such a manner that—when the shutter  6  is open—the radiation from the radiation elements  3   a,    3   b,    3   c  and  3   d  falls on the light sensitive face of the sensing element  2 . The radiation sources  3 ,  3 ′ are connected to the processing device  5  in such a manner that each radiation element  3   a,    3   b,    3   c,    3   d  can be controlled individually by the processor device  5 . Consequently, each radiation element  3   a,    3   b,    3   c,    3   d  can be switched ON or OFF and can be dimmed independently from the other radiation elements  3   a,    3   b,    3   c,    3   d.    
         [0014]    In the test phase a radiation source  3  sends out its light onto the sensing element directly, i.e. not through the lens  8  of the camera  1 . While in the latter case only a small fraction of the matrix would be irradiated, the light will illuminate the whole sensing element  2  when the radiation source  3  is placed inside the camera  1  housing next to the sensing element  2 . 
         [0015]    In the following different test setup variations will be discussed: 
         [0016]    1) Light applied to the camera sensing element  2  can test the whole sensing element  2  or parts of it. 
         [0017]    a. The sensing element  2  shall be tested for safety reasons. This means that the whole picture field or parts of the field shall detect any object within the field. To ensure this function the requirement is that the pixels in the specified field shall respond to the applied light. 
         [0018]    b. When the response from the pixel is detected, the signal passes through the camera processing and the μP processing. Dependent of the signal processing the whole sensing element  2  or part of the sensing element  2  is included in the test. 
         [0019]    2) Variation of shutter time in camera used in 1) can test the whole sensing element  2  or parts of the sensing element  2 . 
         [0020]    a. The camera can be tested as in 1). If light is applied on the camera sensing element  2   a  change in the shutter time will change the response of each pixel in the camera. 
         [0021]    3) Variation of gain in camera used in 1) can test the whole sensing element  2  or parts of the sensing element  2 . 
         [0022]    a. The camera can be tested as in 1). If light is applied on the camera chip a change in the gain will change the response of each pixel in the camera. 
         [0023]    4) Light applied to the edge of the camera chip used in 1) can test the whole sensing element  2  or parts of the sensing element  2 . 
         [0024]    a. The camera can be tested as in 1). In this situation the light is applied from the edge of the camera chip. 
         [0025]    5) On/off modulation of light used in 4) can test the whole sensing element  2  or parts of the sensing element  2 . 
         [0026]    a. When the light is applied as in 4) turning the light source on and off can vary the applied intensity. 
         [0027]    6) Characteristic variation of the light intensity over the camera chip used in 5), can test the whole sensing element  2  or parts of the sensing element  2 . 
         [0028]    a. When the light is applied from the edge of the camera chip as in 5), the intensity will be high close to the light source and weak in a distance from the light source. This gives a characteristic variation of the light intensity over the camera chip. 
         [0029]    b. The characteristic intensity variation can test if some addressing failure is present when the camera chip is read. In some cases addressing failures can result in the same readout from to different pixels despite the light intensity on the two pixels are different. In this case the failure can be revealed. 
         [0030]    7) Light from a specified number of light sources used in 6) can test the whole sensing element  2  or parts of the sensing element  2 . 
         [0031]    a. To ensure revealing of any addressing failure different light sources as in 6) can be combined. This gives light combinations, which are unique for each pixel. 
         [0032]    8) Light from specified positions of light sources used in 7) can test the whole sensing element  2  or parts of the sensing element  2 . 
         [0033]    a. To strengthen uniqueness of the light intensity in 7) positions of the light sources can be specified. 
         [0034]    9) Light sources with different wavelengths used in a given combination and a given time multiplexing used in 8) can test the whole sensor or parts of the sensing element  2 . 
         [0035]    a. To strengthen uniqueness of the light intensity in 8) different wavelength can be used. To separate the wavelength the light sources shall be sequentially turned on and off (Time multiplexing). This will increase the possibility for revealing addressing failures in a color-sensing camera.