KR20060124119A - Method for fast camera preview and apparatus implementing the method - Google Patents

Abstract

A high-speed camera preview method and an apparatus adopting the method are provided to obtain a quick frame rate in a camera preview mode in a dark place. A camera module(150) photographs an image, converts the image into digital data, and has an auto exposure function. An input unit(120) allows a user to input various operating commands. A display unit(130) displays image data photographed by the camera module(150). A memory(140) stores the image data photographed by the camera module(150). A control unit(110) controls the display unit(130) or the memory(140) to display the data from the camera module(150) on the display unit(130) or store the data in the memory(140). The control unit(110) receives information associated with exposure from the camera module(150), and controls an operation associated with the exposure of the camera module(150). When peripheral brightness is not darkened at a uniform level or more, the control unit(110) is operated in an auto exposure state for activating the auto exposure function of the camera module(150). When the peripheral brightness is darkened at the uniform level or more, the control unit(110) is operated in the maximum exposure state for inactivating the auto exposure function of the camera module(150) and fixing a frame rate as a certain frame rate.

Description

High speed camera preview method and apparatus employing the method {Method for fast camera preview and apparatus implementing the method}

1 is a block diagram showing an internal configuration of a device having a digital camera function.

Figure 2 is a graph showing the relationship between the ambient brightness and the frame rate in the camera preview mode, (a) shows the relationship in the conventional device, (b) shows the relationship in the present invention.

3 is a state transition diagram showing the operation in the camera preview mode in the present invention.

4 is a flowchart showing an operation during imaging in the present invention.

<Description of Symbols for Main Parts of Drawings>

110 control unit, 120 input unit,

130 displays, 140 memories,

150 camera modules.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high speed camera preview method and an apparatus employing the method, and more particularly, to a camera preview method and an apparatus employing the method, which perform a camera preview function at high speed and do not deteriorate image quality during imaging.

Various information devices such as a digital camera or a mobile phone, PDA, etc. including the same have a preview function for displaying a screen to be photographed through a display unit such as an LCD before taking a picture. Before taking a picture, the user views the screen shown through the display unit, composes the picture, and then presses the shutter to take the picture.

1 is a block diagram showing the configuration of a device incorporating a digital camera. In general, a terminal device such as a mobile phone or a PDA includes a camera module 150 to implement a digital camera function. For convenience of description, FIG. 1 illustrates a structure of a simple camera module without a lens driver for implementing an optical zoom function.

The optical signal input through the lens 151 is converted into an electrical signal by the imaging unit 153 using an image sensing element such as a CCD (Charge-Coupled Device) or a CMOS sensor. The converted electrical signal is amplified by an AGC (Automatic Gain Control) circuit 155 into an appropriately sized signal and then converted by the A / D converter 156 into a digital signal. The signal processor 157 generates a signal for automatic exposure control using the converted digital signal, for example, information on the overall brightness of the currently input image signal, or transmits the signal to the controller 110 of the apparatus. It converts to the signal of. The I / O 158 serves as an interface for transmitting and receiving data with the controller 110. In addition, the controller 110 may read information on the current gain value and exposure time of the camera module 150 through the I / O 158 and use the information as an information for controlling the operation of the camera module. The exposure controller 154 determines how much the exposure is to be performed according to a signal from the signal processor 157 and a control signal input from the controller 110 through the I / O 158 to drive the imaging unit driver circuit 152. It controls the amount of signal input to the imaging unit 153 through.

The controller 110 displays a signal input from the camera module 150 through the display unit 130 in the preview mode, and informs the camera module 150 when it is detected that the shutter is pressed through the input unit 120. An image capturing operation is performed by capturing an image of the image, and then receiving the captured image data and storing the captured image data in the memory 140 (hereinafter, the term image capturing is used to indicate that the image is captured).

Meanwhile, in the conventional apparatus, the auto exposure function is activated in the camera preview mode to adjust the brightness of the input image signal to an appropriate level. When the user presses the shutter in the camera preview mode, the current preview image is stored in the memory as it is.

However, in a bright place, the time required for the image capturing unit 153 to be exposed to light is shorter than in a dark place in order to receive a signal having an appropriate brightness, so the time required to obtain an image of one screen (frame) is bright. In places it is less than in the dark. Therefore, in the camera preview mode, since the image acquisition time per frame is small in the bright place, the number of frames that can be acquired per unit time is increased (that is, the frame rate is high), and the frame rate is low in the dark place.

Lowering the frame rate means that the speed of changing the screen appearing on the display is slowed down when the user changes the imaging angle to compose the image in the camera preview mode. In places where the surroundings are considerably dark, after a long time after the user changes the imaging angle, the user can view the preview screen at the current imaging angle, which is inconvenient because it takes a long time to compose the desired composition.

SUMMARY OF THE INVENTION The present invention has been made in view of this point, and an object of the present invention is to provide a high speed camera preview method and a device employing the method, which can obtain a fast frame rate in the camera preview mode even in the dark.

In the present invention, when the ambient brightness is darker than a certain level in the camera preview mode, the frame rate is fixed to increase the response speed of the screen even when the ambient brightness is dark. In the case where the ambient brightness is dark, the imaging time is adjusted by adjusting the exposure time and the gain value according to the ambient brightness at the time of actual imaging to prevent deterioration of the image quality at the time of actual imaging.

That is, in the camera preview operation, when the ambient brightness is not dark for a certain period of time, the camera operates in the autoexposure state in which the auto exposure function is activated, and when the ambient brightness is dark for a certain period of time, the auto exposure function is deactivated and at a predetermined frame rate. Operate at maximum exposure with fixed frame rate. In addition, if an image request is made in the camera preview step, the image is captured according to the setting in the camera preview step when the ambient brightness is not dark for a certain level. If the ambient light is dark for a certain level, the exposure time and the gain value are adjusted according to the ambient brightness. Take a picture.

This method can be applied to a general digital camera, a mobile communication terminal having a camera function, a PDA having a camera function, and the like. A device having such a camera function includes a camera module for inputting an image into digital data and having an automatic exposure function, an input unit for inputting various operation commands, and displaying image data photographed by the camera module. A display unit, a memory for storing image data photographed by the camera module, and control to display or store data from the camera module in the display unit, and to receive information related to exposure from the camera module and to receive a camera. A control unit controls an operation related to the exposure of the module. The controller performs the camera preview operation. When the ambient brightness is not dark for a certain time, the controller operates in the auto exposure state in which the auto exposure function of the camera module is activated. If the ambient brightness is dark for a certain time, the control module disables the automatic exposure of the camera module. It operates in the maximum exposure state in which the frame rate is fixed at a predetermined frame rate.

When the controller detects an image pickup request through the input unit during the camera preview operation, the controller controls the camera module according to the setting in the camera preview operation state when the ambient brightness is not dark for a certain level. The exposure time and gain value of the camera module are adjusted accordingly.

Whether the ambient brightness is dark for a certain time or more may be determined according to whether the exposure time is longer than a predetermined time in the auto exposure state. Specifically, when the exposure time is _greater than a predetermined time T _max2 in the automatic exposure state in the camera preview step, the operation is changed to the maximum exposure state, and when the gain value is lower than the predetermined reference value G _ref in the maximum exposure state, the automatic exposure is performed. It works by changing state to state.

If there is an image pickup request during the camera preview operation, the exposure time T _p and the gain G _p in the camera preview step are read from the camera module, and the exposure time T _p is not T _max2 or the gain G _p is not greater than G _ref. The imaging is performed according to the exposure time T _p and the gain G _p . On the other hand, if the exposure time T _p is T _max2 , and the gain G _p is greater than G _ref and not the maximum gain G _max , the proper exposure time T = _{αT max2} x G _p / G _ref and (where α is the gain value change _Image capture with the appropriate gain G = G _ref set. If the exposure time T _p is T _max2 , and the gain G _p is greater than G _ref and the maximum gain G _{max, an} appropriate exposure time T = _{αT max2} x G _p / G _ref , and Y of the final image in the camera preview step If the mean Y _avg of the value is lower than the target value Y _target , the titration gain G = βG _ref x Y _target / Y _avg (β is the rate of change of gain value for 1 / Y change), and the calculated optimal gain G is the maximum. When the gain G _max is exceeded, G = G _max is set, and the image is set by setting the calculated T and G values.

In this case, the exposure time T _max2 is an exposure time corresponding to the maximum frame rate of the camera, and the gain reference value G _ref is a gain value corresponding to the exposure time T _max2 in the autoexposure state. In addition, the exposure time T _max2 may be implemented to be _settable by the user.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 2 is a graph showing the relationship between the ambient brightness and the frame rate in the camera preview mode, (a) shows the relationship in the conventional device, (b) shows the relationship in the present invention.

In the conventional apparatus, as shown in (a), the frame rate is adjusted in proportion to the ambient brightness. In other words, in the conventional device, the automatic exposure mode is always maintained in the camera preview mode, thereby increasing the exposure time for proper exposure in the dark. As a result, the frame rate is lowered.

On the contrary, in the present invention, when the ambient brightness becomes dark and falls below a predetermined frame rate, the automatic exposure mode is released and the frame rate is fixed. Instead, the gain is controlled in inverse proportion to the ambient brightness to adjust the brightness of the camera preview screen. In other words, in the area A of (b), it operates in an autoexposure mode in which the frame rate is controlled in proportion to the ambient brightness as in the prior art, and when the frame rate reaches the predetermined minimum value FR _min2 (that is, the exposure time is the predetermined maximum value). T _max2 ), the auto exposure mode is canceled and the frame rate is fixed to FR _min2 , and the gain value is increased instead (B area). On the other hand, the gain value cannot be increased indefinitely, so if the gain value is the maximum gain value (G _max ) allowed by the camera module, the gain value is not increased any more. On the contrary, when the ambient brightness is brighter in the B area, the gain value decreases gradually, and when the gain value becomes smaller than the gain value G _ref corresponding to the X point, the auto exposure mode is activated again to operate in the A area. To be done.

In FIG. 2, the frame rate FR _min2 corresponding to the X point may be set to any value. That is, it is also possible to set the FR _min2 value to the same value as FR _max so that the camera always operates at the maximum frame rate FR _max in the camera preview mode. In this case, only B region exists in FIG. It is also possible for the user to set the minimum frame rate RF _min2 value to his or her taste.

Next, the operation in the apparatus of the present invention in the camera preview mode will be described with reference to FIG. 3 is a state transition diagram showing the operation in the camera preview mode in the present invention.

First, when the user selects the camera preview mode, the device enters the auto exposure state S310 and performs the operation in the auto exposure mode, that is, the operation in the area A of FIG. That is, in the automatic exposure state (S310) to perform the operation in the same manner as the conventional. On the other hand, in this state, the controller 110 continuously reads the information on the current exposure time from the camera module 150 to check whether the exposure time exceeds the predetermined maximum exposure time.

If the ambient brightness becomes dark so that the exposure time becomes T _max2 or more, which is a time corresponding to the frame rate FR _min2 , the controller 110 releases the auto exposure mode and the camera module 150 so that the exposure time becomes T _max2 . By entering a control command to enter the maximum exposure state (S320). In the maximum exposure state S320, the exposure time is fixed at T _max2 , that is, the frame rate is fixed at RF _min2 , and only the gain is adjusted by the AGC when the ambient brightness becomes dark. On the other hand, in this state, the controller 110 continuously reads the information on the current gain value from the camera module 150 and continuously checks whether the gain value falls below the predetermined reference gain value G _ref .

If, in the maximum exposure state (S320), the ambient brightness becomes bright again and the gain value is lowered by less than G _ref by the AGC, the controller 110 issues a control command to the camera module 150 to activate the auto exposure mode again. Send and enter the automatic exposure state (S310).

By this operation, the apparatus of the present invention operates in the area A when the ambient brightness is greater than the predetermined brightness as shown in FIG. 2 (b), and operates in the area B otherwise.

Meanwhile, when an operation for requesting imaging from a user is input while performing such an operation, the device may be out of the camera preview mode and perform a camera imaging operation. The operation at this time will be described with reference to FIG. 4 is a flowchart showing an operation during imaging in the present invention.

If the device was operating in the area A when the user requested an image pickup, the variable values such as the current gain G _p and the exposure time T _p of the camera module as shown in the camera preview mode as in the prior art (hereinafter, The image is taken as the 'current setting value'. On the other hand, if the device was operating in area B, the gain and exposure time according to the current ambient brightness are calculated and the image is taken accordingly.

To this end, if there is an imaging request from the user, the controller 110 reads the current setting value from the camera module 150 (S401). If the exposure time T _p is not T _max2 (No in step S403), the device indicates that the device is operating in the area A, and the image is captured according to the current setting value (S410).

On the other hand, if the exposure time T _p is T _max2 (YES in step S403), the device indicates that it is operating in the B region, so it is checked whether the gain G _p is greater than G _ref (S405). If the gain G _p is not greater than G _ref , it indicates that the device is at point X or not at least in the area B. Therefore, the process goes to step S410 to take an image according to the current setting value.

On the other hand, if the gain G _p is greater than G _ref , the device indicates that it is in the B area, and thus the proper exposure time and gain are calculated without taking an image according to the current setting value. First, since the gain value is inversely proportional to the ambient brightness, the current proper exposure time T for the exposure time at the X point from the current gain G _p for the gain G _ref at the X point is calculated by Equation 1 (S407). ).

T = T _max2 x G _p / G _ref

On the other hand, depending on the device, since the proper exposure time can be changed at a predetermined ratio with respect to the ratio of the gain value, in this case, it is calculated by the equation (2).

T = _{αT max2} x present gain value / G _ref

Where α represents the rate of change of exposure time with respect to a change in gain value.

On the other hand, the optimal gain uses the reference gain value G _ref corresponding to the gain value at the point X if the current gain G _p is lower than the maximum gain value G _max . The gain value is determined accordingly.

In other words, if the gain G _p is not G _max (No in step S409), the proper gain G is set to G _ref (S411), and the image is captured after setting the camera module with the exposure time T and the gain G (S430).

On the other hand, if the gain G _p is G _max , the average of the Y values of the final image input in the camera preview mode (Y is determined to determine whether the ambient brightness is darker than the minimum brightness that can guarantee proper exposure by the maximum gain value G _max . _avg ) is determined to be smaller than the average Y _target of the Y value in the appropriate exposure state (S421). If the average Y _avg of the Y value of the final preview image is equal to or higher than the average Y _target of the Y value at the appropriate exposure state, it indicates that the final preview image was taken with sufficient exposure to obtain an appropriate gain G. At G _ref (S411), the camera module is set to the appropriate exposure time T calculated in step S407 and then image is captured (S430).

On the other hand, if Y _avg is smaller than Y _target , it means that a sufficient exposure is not secured even when the camera is in the camera preview mode set to the maximum gain. Therefore, the proper gain value G is calculated according to Equation 3 (S423). .

G = G _ref x Y _target / Y _avg

On the other hand, according to the apparatus and the ratio of the G value of the ratio and G _ref for the Y _target of Y _avg value may have a corresponding relationship between the certain rate, in this case, reflects the ratio corresponding relationship as shown in Equation (4) You should.

G = βG _ref x Y _target / Y _avg

Β represents the rate of change of the gain value with respect to the change of 1 / Y _avg .

On the other hand, since the gain value settable to the camera module 150 is the maximum gain value G _max , when the gain value calculated by Equation 3 or 4 exceeds the maximum gain value G _max (YES in step S425). ) Set the gain value G to G _max (S427), otherwise use the gain value G calculated by equation (3) or equation (4). The imaging operation is performed with appropriate exposure by setting the appropriate gain G and the appropriate exposure T calculated in step S407 to the camera module 150 after imaging (S430).

As mentioned above, although this invention was demonstrated to the several example, this invention is not limited to a specific Example. Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the invention.

As described above, according to the present invention, it is possible to increase the response speed of the camera preview mode in a dark place by controlling the camera preview mode so that it does not fall below the minimum frame rate without any inconvenience, even in the dark. When shooting at a location, it is possible to prevent the deterioration of the image quality in actual shooting by not shooting with the setting in the camera preview mode but calculating the exposure time and gain value appropriate to the current brightness and shooting accordingly.

Claims (17)

In the camera preview operation, if the ambient brightness is not dark for a certain period of time, the camera operates in auto exposure with the autoexposure function activated. If the ambient brightness is dark for a certain time, the auto exposure function is disabled and the frame rate is set to a predetermined frame rate. A camera preview step of operating at a fixed maximum exposure state, If there is an image request in the camera preview step, the image is taken as set in the camera preview step if the ambient brightness is not dark for a certain level. If the ambient light is dark for a certain level, the exposure time and the gain value are adjusted according to the ambient brightness. A high speed camera preview method comprising the step of imaging. The high speed camera preview method of claim 1, wherein whether the ambient brightness is dark for a predetermined time or more is determined based on whether the exposure time is longer than a predetermined time in the auto exposure state. The method of claim 1, wherein in the camera preview step When the exposure time is over T _max2 in the auto exposure state, it _operates by changing the state to the maximum exposure state. And in the maximum exposure state, when the gain value is lower than the predetermined reference value G _ref , the high speed camera preview method operates by changing the state to the automatic exposure state. The method of claim 3, wherein the imaging step Reading the exposure time T _p , the gain G _p at the camera preview step, And if the exposure time T is _p T _max2 has no or gain G _p is larger than G _ref comprising: an image pick-up in the exposure time T _p, the gain G _p, When the exposure time T _p is T _max2 and the gain G _p is greater than G _ref and not the maximum gain G _max , the proper exposure time T = _{αT max2} x G _p / G _ref and (where α is the exposure time for the gain value change). The image pickup rate by setting the proper gain G = G _ref , If the exposure time T _p is T _max2 and the gain G _p is greater than G _ref and the maximum gain G _max, then the proper exposure time T = _{αT max2} x G _p / G _ref , and the Y value of the final image in the camera preview step If the average Y _avg is lower than the target value Y _target , the titration gain G = βG _ref x Y _target / Y _avg (β is the rate of change of the gain value for 1 / Y change), and the calculated optimal gain G is the maximum gain G. _{When max} is exceeded, G = G _max , and the imaging is performed by setting the calculated T and G values. High speed camera preview method comprising a. The method of claim 4, wherein The exposure time T _max2 is the exposure time corresponding to the maximum frame rate of the camera. The method of claim 4, wherein And a gain reference value G _ref is a gain value corresponding to the exposure time T _max2 in the autoexposure state. The method of claim 4, wherein The exposure time T _max2 is a user-configurable high speed camera preview method. The method of claim 4, wherein A high speed camera preview method, wherein α = 1 and β = 1. A camera module which inputs an image, converts it into digital data, and has an automatic exposure function; An input unit for inputting various operation commands, A display unit for displaying image data photographed by the camera module; A memory for storing image data photographed by the camera module; A control unit configured to display data from the camera module on the display unit or to store the data in the memory, to receive information related to the exposure from the camera module, and to control an operation related to the exposure of the camera module; The control unit performs a camera preview operation, when the ambient brightness is not dark for a certain period of time, the controller operates in an autoexposure state in which the auto exposure function of the camera module is activated. And deactivation and operating in a maximum exposure state in which the frame rate is fixed at a predetermined frame rate. The method of claim 9, When the controller detects an image pickup request through the input unit during the camera preview operation, the controller controls the camera module according to the setting in the camera preview operation state when the ambient brightness is not dark for a certain level. The apparatus having a camera function, characterized in that for imaging by adjusting the exposure time and the gain value of the camera module according to the brightness. The apparatus of claim 10, wherein the controller determines whether the ambient brightness is dark for a predetermined time or more depending on whether the exposure time of the camera module is greater than or equal to a predetermined time in the automatic exposure state. The method according to claim 10 or 11, wherein The control unit changes the state to the maximum exposure state when the exposure time exceeds a predetermined time T _max2 in the automatic exposure state during the camera preview operation, and automatically _operates when the gain value is lower than the predetermined reference value G _ref in the maximum exposure state. A device having a camera function, which is operated by changing a state into a state. The method of claim 12, wherein the controller is further configured to detect an image pickup request through an input unit during a camera preview operation. Reads the exposure time, T _p, the gain G _p in the camera preview stage, if the exposure time T _p is T _max2 have no or gain, G _p is greater than G _ref and the imaging as the exposure time, T _p, the gain G _p If the exposure time T _p is T _max2 and the gain G _p is greater than G _ref and not the maximum gain G _max , the proper exposure time T = _{αT max2} x G _p / G _ref and (where α is the exposure to the change in the gain value). Imaging time with the proper gain G = G _ref , and when the exposure time T _p is T _max2 and the gain G _p is greater than G _ref and the maximum gain G _{max, the} appropriate exposure time T = _{αT max2} x G _p / G _ref , and if the average Y _avg of the Y value of the final image in the camera preview step is lower than the target value Y _target , the appropriate gain G = βG _ref x Y _target / Y _avg (β is 1 / Y rate of change of the gain value for the change), when the calculated appropriate gain G exceeds the maximum gain G _max An apparatus having a camera function, characterized by setting G = G _max and setting the calculated T and G values. The method of claim 13, The exposure time T _max2 is an exposure time corresponding to the maximum frame rate of the camera. The method of claim 13, And a gain reference value G _ref is a gain value corresponding to the exposure time T _max2 in the autoexposure state. The method of claim 13, The exposure time T _max2 is a device having a camera function, characterized in that the user can set. The method of claim 13, α = 1, β = 1 device with a camera function.

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