Patent Publication Number: US-2002003962-A1

Title: Control method of CCD camera

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a CCD (Charge-Coupled Device) camera, and in particular to a control method of a CCD camera which is capable of compensating a focus error in accordance with the use or not of an OLPF (Optical Low Pass Filter) by adjusting control traces of a zoom lens and a focus lens in automatic adjustment of a focus condition and a zoom condition of the CCD camera.  
       [0003] 2. Description of the Prior Art  
       [0004]FIG. 1 is a perspective sectional view illustrating the internal structure of a typical lens unit in accordance with the prior art.  
       [0005] As depicted in FIG. 1, the general lens unit in accordance with the prior art includes a zoom lens  11  imaging an object so as to be enlarged or reduced in size, a focus lens  12  adjusting a focus of an image of the object incident through the zoom lens  11 , an OLPF (Optical Low Pass Filter)  13  filtering the image so as to be pass only that light visible to the eyesight of humans by blocking light in the infrared region in photographing of the object incident through the focus lens  12 , and a CCD (Charge Coupled Device)  14  converting a quantity of light of the image of the object incident through the OLPF  13  into an electric signal. The operation of the general lens unit in accordance with the prior art will now be described.  
       [0006] First, the CCD  14  converts a quantity of light of the image of the object incident through the lens unit into an electrical signal, and outputs the electrical signal. Herein, the lens unit has an exchangeable structure, whereby a clear image can be photographed through the lens unit including the OLPF  14  under the circumstances of having a sufficient illumination (i.e., a color picture can be photographed) such as in the daytime.  
       [0007] On the contrary, in the low illumination circumstances having only a little illumination (i.e., when photographing a color picture is meaningless) such as during the nighttime, the lens unit including the OLPF  13  has to be replaced by a lens unit without an OLPF (Optical Low Pass Filter) in order to photograph with use of light in the infrared region. Herein, because a glass having a refractive index the same as the OLPF  13  is inserted into the position of the OLPF  13  in the lens unit, the focus of an image focused on the CCD  14  can be maintained as it is without a special operation besides replacing the lens unit.  
       [0008] However, in the prior art, because the lens unit has to be changed every time when a color photographing is meaningless according to an illumination condition such as in the daytime or the nighttime, it is troublesome for a user. The conventional art for compensating the above-mentioned problem will now be described with reference to accompanying FIG. 2.  
       [0009]FIG. 2 is a sectional view illustrating the internal structure of a lens unit which attempts to compensate for the shortcoming the lens unit of FIG. 1.  
       [0010] As depicted in FIG. 2, this further lens unit in accordance with the prior art includes a zoom lens  11  imaging an object so as to be enlarged or reduced, a focus lens  12  adjusting a focus of the image of the object incident through the zoom lens  11 , a motor  23  connected to a threaded shaft  25 , a movable plate  24  carrying an OLPF (Optical Low Pass Filter)  21  and a glass  22 , installed on the shaft  25  and moving up and down or right and left along the thread of the shaft  25  according to a rotation direction of the motor  23 , and a CCD (Charge Coupled Device)  14  converting a quantity of light of the image of the object incident through the OLPF  21  or the glass  22  into an electric signal.  
       [0011]FIG. 3 is a graph illustrating an example of control trace data according to the use or not of the conventional OLPF. In the prior art, movement of the zoom lens  11  and the focus lens  12  is adjusted by applying the same control trace  30  in the daytime (high illumination state) and the nighttime (low illumination state). For example, because the OLPF  21  is used only in the daytime and the glass  22  having the same refractive index as the OLPF  21  is used only in the nighttime instead of the OLPF  21 , the movement of the focus lens  12  and the zoom lens  11  is adjusted by applying the same control trace  30  regardless of whether it is the daytime and the nighttime. The operation of the lens unit in accordance with the prior art will now be described with reference to accompanying FIG. 3.  
       [0012] First, the OLPF  21  and the glass  22  built inside the moving plate  24  are moved by the motor  23  according to a photographing mode of a CCD (Charge-Coupled Device) camera. In more detail, the motor  23  transfers the moving plate  24  according to rotation of the shaft  24  having the thread in order to let the light of the image be incident only through the OLPF  21  in the daytime. Herein, the glass  22  has the same refractive index as the OLPF  21  in order to adjust refraction of the light incident through the focus lens  12 .  
       [0013] On the contrary, the moving plate  24  is transferred according to rotation of the shaft  25  having the thread in order to let the light of the image be incident only through the glass  22  in the nighttime. In more detail, by lefting the light be incident on the CCD  14  through the OLPF  21  or the glass  22  of the moving plate  24  in accordance with the daytime mode or the nighttime mode, the lens unit changing problem can be solved.  
       [0014] However, in view of miniaturization and low price trends of camera products, when the in addition to glass  22  (i.e. “dummy filter”) for adjusting the refractive index of the lens group is added to the camera lens the OLPF  21  affecting directly to an image, the unit cost of production of the CCD camera increases. In addition, the size of the CCD camera is increased by adding the glass  22 , and thus it is disadvantageous to the miniaturization of camera.  
       [0015] As described above, in the CCD camera in accordance with the prior art, because the user has to change the lens unit according to the daytime mode or the nighttime mode, namely, depending upon the illumination condition, it is troublesome for the user.  
       SUMMARY OF THE INVENTION  
       [0016] Accordingly, it is an object of the present invention to provide a control method of a CCD (Charge-Coupled Device) camera which is capable of heightening a facility of a user and facilitating a price reduction and miniaturization of a camera by removing a glass element unaffecting directly to the quality of an image, including an OLPF (Optical Low Pass Filter) directly affecting the quality of an image inside a lens unit of a CCD (Charge-Coupled Device) camera, and compensating a focus error occurring due to the removal of the glass element by adjusting a control trace of a zoom lens and a focus lens.  
       [0017] In order to achieve the above-mentioned object, a control method of a CCD (Charge-Coupled Device) camera in accordance with the present invention includes detecting an illumination of a photographing region, converting a photographing mode of a CCD (Charge-Coupled Device) camera into a daytime mode or a nighttime mode by judging whether the detected illumination is less than a pre-stored reference illumination value, loading first trace data pre-stored in a memory so as to photograph the photographing region through an OLPF (Optical Low Pass Filter) when the photographing mode is converted into the daytime mode, loading second trace data pre-stored in the memory so as to photograph the photographing region without using the OLPF when the photographing mode is converted into the nighttime mode, and adjusting a focus of a lens of the CCD camera on the basis of the loaded first trace data and the second trace data. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0018]FIG. 1 is a perspective sectional view illustrating the internal structure of a typical lens unit in accordance with the prior art;  
     [0019]FIG. 2 is a sectional view illustrating the internal structure of an improved lens unit according to the prior art;  
     [0020]FIG. 3 is a graph illustrating an example of control trace data of a lens unit according to the use of the conventional OLPF (Optical Low Pass Filter);  
     [0021]FIG. 4A is a schematic sectional view illustrating a lens unit in order to describe a focal distance according to the use of an OLPF (Optical Low Pass Filter);  
     [0022]FIG. 4B is a schematic sectional view illustrating a lens unit in order to describe a focal distance according to the use or not of a dummy glass;  
     [0023]FIG. 5 is a schematic block diagram illustrating a control apparatus of a CCD (Charge-Coupled Device) camera in accordance with the present invention;  
     [0024]FIG. 6 is a graph illustrating an example of control trace data according to the use of an OLPF; and  
     [0025]FIG. 7 is a flow chart illustrating a control method of a CCD (Charge-Coupled Device) camera in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0026] Hereinafter, an embodiment of the present invention will be described with reference to accompanying FIGS.  4 - 7 .  
     [0027]FIG. 4A is a schematic sectional view illustrating a lens unit in order to describe a focal distance according to the use of an OLPF (Optical Low Pass Filter).  
     [0028]FIG. 4B is a schematic sectional view illustrating a lens unit in order to describe a focal distance according to the use or not of a dummy glass.  
     [0029] First, because light incident through a zoom lens  31  and a focus lens  32  is refracted through an OLPF (Optical Low Pass Filter)  33 , an incidence angle of the light is varied, and a focal distance of the lens group is made longer in accordance with the varied incidence angle. Herein, the OLPF  33  carried inside a movable plate  41  and is mechanically switched in or out of the optical path of the lens group accordance with the conversion of the photographing mode of a CCD (Charge-Coupled Device) camera such as between a daytime mode or a nighttime mode.  
     [0030] Accordingly, in determining the control trace of the focus lens  32  and the zoom lens  31 , an accurate focal distance  35 A is set by calculating the increased focal distance through the OLPF  34 . In more detail, in the daytime the OLPF  33  is used, but in the nighttime the OLPF  33  is moved out of the optical path in order to let an unfiltered image of an object be incident on the CCD  34  through the focus lens  32  (In the nighttime the OLPF  33  and a dummy glass are not used.) Herein, as depicted in FIG. 4B, because the focal distance (focal length  37 A is shortened by the movement of the OLPF  33 , a clearly focused image (photographing region) can not be obtained with a fixed control trace  31  in accordance with the prior art.  
     [0031] Herein, the focal distances  35 A,  37 A can be varied in accordance with a refraction characteristic of the OLPF  33 , the zoom lens  31  and the focus lens  32 . In more detail, a focus error of the lens occurs in case of the use or not of the OLPF.  
     [0032]FIG. 5 is a block diagram illustrating a control apparatus of a CCD (Charge-Coupled Device) camera in accordance with the present invention.  
     [0033] As depicted in FIG. 5, the control apparatus of the CCD camera includes a zoom lens  31  imaging an object so as to be enlarged or reduced, a focus lens  32  adjusting a focus of the image of the object incident through the zoom lens  11 , an OLPF (Optical Low Pass Filter)  33  filtering the image so as to pass only that light visible to the eyesight of human by blocking light in the infrared region in imaging the object with the focus lens  32 , a first motor  38  connected to a threaded shaft  42 , a movable plate  41  carrying the OLPF  33 , installed on the shaft  42  and moving up and down and right and left along the thread of the shaft  42  by a rotation/reverse rotation of the first motor  38 , a CCD (Charge Coupled Device)  34  converting a quantity of light of an image of an object incident through the OLPF  33  or the focus lens  32  into an analog signal, an A/D (analog to digital) converting unit  35  converting the analog signal outputted from the CCD  34  into digital image data, an illumination detecting unit  36  detecting an illumination value of the digital image data, a microcomputer  37  setting a photographing mode of the camera as the daytime mode or the nighttime mode on the basis of comparing the detected illumination value and a pre-stored reference illumination value, controlling the operation of the first motor  38  according to the set photographing mode and outputting a control signal for controlling a movement of the zoom lens  31  and the focus lens  32  according to the photographing mode by loading pre-stored first trace data or pre-stored second trace data of the lens, and a second motor  39  and a third motor  40  moving the zoom lens  31  and the focus lens  32 , respectively according to a control signal from the microcomputer  37 .  
     [0034] Hereinafter, the first and the second trace data used according to the use or not of the OLPF  33  will now be described in detail with reference to accompanying FIG. 6.  
     [0035]FIG. 6 is a graph illustrating an example of control trace data according to the use of the OLPF  33 . Herein, the OLPF  33  is used in order to photograph an object so as to be similar to what is seen by the eyesight of a human by blocking infrared rays in the daytime mode.  
     [0036] As depicted in FIG. 6, in the control method of the CCD camera in accordance with the present invention, a clear image (photographing region) can be photographed regardless of the daytime mode and the nighttime mode by setting different traces  61 ,  62  and adjusting the movement of the zoom lens  31  and the focus lens  32  according to the set traces  61 ,  62 . Herein, the second and the third motors  39 ,  40  respectively control (adjust) the zoom lens  31  and the focus lens  32  according to the set traces  61 ,  62 .  
     [0037] The first trace data and the second trace data about each trace  61 ,  62  is pre-stored in a memory (not shown) of the microcomputer  37  as a map format, and the focus of the lens is adjusted by moving the zoom lens  31  and the focus lens  32  by switching between each trace  61 ,  62  whenever the photographing mode is converted into the daytime mode or the nighttime mode. Herein, the first trace data and the second trace data are data for adjusting the movement of the zoom lens  31  and the focus lens  32  in order to make a focus of the lens be varied according to the movement (mechanical switching) of the OLPF  33  to correspond to the focal imaging plane of CCD  34 . In more detail, because the movement of the zoom lens  31  and the focus lens  32  is adjusted by loading the first trace data and the second trace data pre-stored in the memory according to the daytime mode or the nighttime mode, there is no need to use the glass  36 A.  
     [0038] Hereinafter, the operation of the control apparatus of the CCD camera in accordance with the present invention will now be described in more detail with reference to accompanying FIG. 7.  
     [0039]FIG. 7 is a flow chart illustrating the control method of the CCD camera in accordance with the present invention. In more detail, in order to convert the photographing mode of the CCD camera into the daytime mode or the nighttime mode, only the OLPF  33  is used without using the glass  36 A and an object (photographing region) is photographed after automatically adjusting the focal distance of the lens.  
     [0040] First, the illumination-detecting unit  36  detects the illumination of digital image data (photographing region) outputted from the A/D converting unit  35  as shown at step S 71 . Herein, a region having a high illumination is defined as a visible ray region, and photographing of the object in the visible ray region through the OLPF  33  is the daytime mode. On the contrary, a region having a low illumination is defined as an infrared ray region, and photographing of the object in the infrared ray region without the light passing through the OLPF  33  and the glass  36 A is the nighttime mode.  
     [0041] After that, the microcomputer  37  judges whether the illumination detected by the illumination-detecting unit  36  is less or greater than the pre-stored reference illumination value, as shown at step S 72 . Herein, the reference illumination value, the first trace data and the second trace data are stored in the memory (not shown) of the microcomputer  37 . In addition, the reference illumination value is set by considering (calculating) various factors (an aperture of a camera, a magnifying power of a camera lens, a focus length of a lens unit, etc.) in a production process of the camera.  
     [0042] When the detected illumination value is not less than the reference illumination value, the microcomputer  37  converts the photographing mode of the camera into the daytime mode as shown at step S 73 . In more detail, in the daytime mode, the microcomputer  37  controls the first motor  38  in order to make the plate  41  including the OLPF  33  move along the thread of the shaft  42 . Herein, the plate  41  carrying the OLPF  33  is moved into the optical path in order to cause the light of an image of an object incident through the focus lens  32  be incident on the CCD  34  through the OLPF  33 .  
     [0043] When the photographing mode of the CCD camera is converted into the daytime mode as shown at S 73 , the microcomputer  37  loads the first trace data pre-stored in the memory, as shown at step S 64  and adjusts the movement of the zoom lens  31  and the focus lens  32  by controlling the second and the third motors  39 ,  40  according to the loaded first trace data, as shown at step S 77 . Herein, the first trace data is data for compensating a focus error of the lens varied while the image of the object is incident on the CCD  34  through the OLPF  33 .  
     [0044] When the detected illumination value is not greater than the reference illumination value, the microcomputer  37  converts the photographing mode of the CCD camera into the nighttime mode, as shown at step S 75 . In more detail, in the nighttime mode, the microcomputer  37  controls the first motor  38  so as to make the plate  41  including the OLPF  33  move along the thread of the shaft  42 . Herein, the plate  41  carrying the OLPF  33  is moved out of the optical path so as to cause the light of the image of the object incident through the focus lens  32  be directly incident on the CCD  34  without passing through the OLPF  33 .  
     [0045] When the photographing mode of the camera is converted into the nighttime mode as shown at step S 75 , the microcomputer  37  loads the second trace data pre-stored in the memory as shown at step S 76 , and adjusts the movement of the zoom lens  31  and the focus lens  32  of the CCD camera by controlling the second and the third motors  39 ,  40  according to the loaded second trace data, as shown at step S 77 . Herein, the second trace data is data for compensating a focus error of the lens varied while the image of the object is incident directly on the CCD  34  through the focus lens  32  (not passing through the OLPF  33 ).  
     [0046] As described above, a control method of a CCD camera in accordance with the present invention can provide enhanced facility for a user by converting a photographing mode of a camera into a daytime mode or a nighttime mode without changing a lens unit each time (uninstalling a dummy glass in the nighttime) by controlling a movement of a zoom lens and a focus lens  32 .  
     [0047] In addition, because there is no need to install a dummy glass in order to adjust a refractive index of the lens group, the control method of the CCD camera in accordance with the present invention can reduce a production cost by eliminating the use of a dummy filter glass.  
     [0048] In addition, because there is no need to install a dummy filter glass in order to adjust a refractive index, the control method of the CCD camera in accordance with the present invention can permit minimizing the size of a CCD (Charge-Coupled Device) camera.