KR100966342B1 - Method for controlling LED flash - Google Patents

Abstract

The present invention relates to a LED flash control method, and more particularly, to measure the brightness of a subject in a torch mode without the addition of a separate device such as a dimming sensor, and to capture a capture mode from the measured brightness of the subject. The present invention relates to a method of controlling an LED flash that turns on a flash by calculating a current value required for a mode and adjusting a current value according to a distance so that a subject has a constant brightness in a capture mode regardless of the distance between the flash and the subject.

To this end, the LED flash control method according to the invention, (a) turning on the flash in the torch mode (torch mode); (b) measuring the brightness of the subject in the torch mode; (c) calculating a current value required for a capture mode from the brightness of the subject measured in step (b); (d) setting the current value calculated in step (c) to a flash driver IC; and (e) turning on the flash in the capture mode according to the current value set in the flash driver IC in step (d). It characterized in that it comprises a step.

LED flash, torch mode, capture mode, brightness, calibration

Description

LED flash control method {Method for controlling LED flash}

The present invention relates to a LED flash control method, and more particularly, to measure the brightness of a subject in a torch mode without the addition of a separate device such as a dimming sensor, and to capture a capture mode from the measured brightness of the subject. The present invention relates to a method of controlling an LED flash that turns on a flash by calculating a current value required for a mode and adjusting a current value according to a distance so that a subject has a constant brightness in a capture mode regardless of the distance between the flash and the subject.

Recently, with the development of mobile communication technology, a mobile communication terminal is developed in which a plurality of electronic devices, which had to be provided separately from the mobile communication terminal, are combined with a mobile communication terminal, for example, a function such as listening to a radio, watching TV, or playing an MP3. In particular, a camera phone having a camera function added to a mobile communication terminal has been developed and widely used.

In particular, the adoption of high pixel cameras has increased due to the advanced cameras embedded in mobile communication terminals, and such high pixel cameras require the same level of image quality as digital cameras.

When taking a picture using the camera built in the mobile terminal, if the brightness of the surrounding environment is not suitable for taking pictures, the flash is used to adjust the brightness of the picture suitable for taking pictures. Xenon flash or LED flash is used as the flash to create camera-level night-time image quality. Among them, LED flashes having advantages in terms of size and the like are being used more as camera flashes embedded in mobile communication terminals.

Hereinafter, the LED flash control method according to the conventional method will be described in more detail with reference to the accompanying drawings.

Figure 1 shows a flow chart of the LED flash control method according to the conventional method.

When the user selects the flash on mode for taking a picture (S100), and inputs a capture command (S110), first, auto focusing, that is, finding an optimal focus position of the lens for shooting and moving the lens to that position is performed. When the capture (capture), the flash is turned on with less light than the amount of light (S120), such a state is called torch mode. The amount of light in the flash in torch mode is approximately 50% compared to the amount of light in the flash at capture.

After performing the auto focusing operation in the torch mode (S130), the flash is turned on for capturing (S140). This state is called a capture mode. After the flash is turned on in the capture mode, capture is performed (S150) to capture a desired subject.

According to the LED flash control method according to the conventional method, the amount of light of the flash in the capture mode is always constant regardless of the distance between the flash and the subject and the brightness of the surrounding environment. Accordingly, even if the brightness of the subject is appropriate when capturing a distant subject, deterioration of the photographed image may occur due to the amount of flash light that is higher than necessary when capturing the subject at a close distance.

That is, according to the conventional LED flash control method, the flash is turned on with a fixed amount of light in both the torch mode and the capture mode. In particular, the flash is turned on with a brightness that is not suitable for shooting a subject at a close range. .

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and measures the brightness of the subject in the torch mode without the addition of a separate device such as a dimming sensor, and the current value required for the capture mode from the measured subject brightness. The purpose of the present invention is to provide a control method of LED flash that turns on the flash by adjusting the current value according to the distance so that the subject has a constant brightness in the capture mode regardless of the distance between the flash and the subject.

As a technical configuration for achieving the above object, the LED flash control method according to the present invention comprises: (a) turning on the flash in a torch mode; (b) measuring the brightness of the subject in the torch mode; (c) calculating a current value required for a capture mode from the brightness of the subject measured in step (b); (d) setting the current value calculated in step (c) to a flash driver IC; and (e) turning on the flash in the capture mode according to the current value set in the flash driver IC in step (d). It characterized in that it comprises a step.

The LED flash control method may further include an autofocusing step of moving the lens to the optimal focus position by finding the optimal focal position of the lens (f) between the step (a) and the step (b). have.

The LED flash control method may further include an autofocusing step of moving the lens to the optimal focus position by finding the optimal focus position of the lens (f) between the step (d) and the step (e). have.

Here, a constant current value may be used in step (a).

The step (c) may include: (c1) calculating a brightness to be corrected from a difference between the brightness of the subject measured in the step (b) and a preset reference brightness; (c2) calculating a current value to be corrected from the brightness to be corrected calculated in step (c1); and (c3) calculating the current value to be corrected calculated in step (c2) in step (a). It may include; in addition to the current value used.

Here, the current value to be corrected in step (c2) may be obtained by multiplying the brightness to be corrected by a preset correction constant.

Here, the preset correction constant is (I2-I1) / (B2-B1) (where I1 and I2 are different current values set in the flash driver IC,

 B1 is the brightness of the subject when the current value is I1, and B2 is the brightness of the subject when the current value is I2.

LED flash control method according to the present invention measures the brightness of the subject in the torch mode without the addition of a separate device such as a dimming sensor, calculates the current value required for the capture mode from the measured brightness of the subject to the distance between the flash and the subject Regardless of the capture mode, the LED flash control method is provided to adjust the current value according to the distance so that the subject has a constant brightness.

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

2 shows a schematic structure of a camera 200 including an LED flash.

The camera 200 including the LED flash shown in FIG. 2 includes a back end 210, an image processor 220, and a flash 230.

The back end unit 210 receives a command to be performed from a user interface (not shown) of the camera and transmits the command to the image processing unit 220 of the camera.

The image processor 220 receives the command from the back end unit 210 to perform auto focusing in the torch mode. When the auto focusing operation is completed, the image processing unit 220 switches the flash state from the torch mode to the capture mode and adjusts the brightness of the subject to be described later. It measures and calculates the current required for the capture mode.

The flash unit 230 emits light by a desired amount of light in the torch mode or the capture mode under the control of the image processor 220. The flash unit 230 includes a flash driver IC 231 and a flash 232, and the flash driver IC 231 receives a current value from the image processor 220 and flashes the light with a light amount corresponding to the current value. ) To turn on.

Figure 3 shows a flow chart of the LED flash control method according to an embodiment of the present invention.

When the user selects a flash on mode for taking a picture (S300) and inputs a capture command (S310), the image processing unit 220 first flashes in a torch mode that emits light with less light than the capture mode to perform auto focusing. 232) is turned on (S320).

When the flash 232 is turned on in the torch mode, the image processing unit 220 performs an auto focusing operation (not shown). The auto focusing operation may include measuring a brightness of a subject in a torch mode to be described later (S330), calculating a current value necessary for a capture mode from the measured subject brightness (S340), and calculating the calculated current value using a flash driver IC. It may be performed after the step S350 set in step 231.

When the auto focusing operation is completed, the image processor 220 measures the brightness of the subject while maintaining the torch mode without switching to the capture mode (S330). The brightness of the subject includes all information about the distance from the flash to the subject and the brightness of the surrounding environment. The brightness of the flash can be calculated to obtain the optimum brightness of the subject in the capture mode.

When the brightness of the subject is measured in the torch mode, the image processor 220 calculates a current value required for the capture mode from the measured brightness of the subject (S340).

More specifically, the image processor 220 first calculates the brightness to be corrected from the difference between the measured brightness of the subject and the preset reference brightness (S341). The preset reference brightness is preferably Y125 to Y140 when the Y level in the darkest state is Y0 and the Y level in the brightest state is Y255.

After calculating the brightness to be corrected, the image processor 220 calculates a current value to be corrected from the brightness to be corrected (S342). The following describes how to calculate the current value to be corrected from the brightness to be corrected together with the actual data.

Table 1 below shows how the difference in brightness of the subject in the capture mode and the torch mode changes depending on the distance from the flash to the subject. In capture mode, 700mA was set in the flash driver IC 231, and in torch mode, 300mA was set.

TABLE 1

Distance from flash to subject (cm)
Subject brightness (Y) Capture mode Torch mode Brightness difference 10 251 153 98 30 212 109 103 60 170 53 117 100 107 7 100

Since the brightness difference of the subject has a value from 98Y to 117Y, it can be seen from Table 1 that the brightness difference of the subject in the capture mode and the torch mode has a similar value regardless of the distance from the flash to the subject. That is, this indicates that the brightness of the subject also has a constant difference if the current value set in the flash driver IC 231 has a constant difference regardless of the distance from the flash to the subject.

 Table 2 below shows a relationship between the current value mA set in the flash driver IC 231 and the brightness Y of the subject according to the distance from the flash to the subject.

TABLE 2

Current (mA) 10 cm 30 cm 60 cm 100 cm 700 251Y 212Y 170Y 107Y 300 153Y 109Y 53Y 7Y Brightness change per 100 mA 24.5Y 25Y 29Y 24Y

The change in brightness per 100 mA is approximately 25 Y. From Table 2, it can be seen that an additional 4 mA of current must be applied to increase the brightness by 1 Y. That is, this value can be used as a correction constant to obtain a current value to be corrected from the brightness to be corrected. The current value to be corrected in step S342 can be obtained by multiplying the brightness constant to be corrected here. . Further, from Table 2, I1 and I2 are referred to as different current values set in the flash driver IC 231 at a constant distance, and B1 and B2 are in each case where the current values of I1 and I2 are set in the flash driver IC 231. In terms of the brightness of the subject, it is generally understood that the correction constant is given by (I2-I1) / (B2-B1).

After calculating the current value to be corrected (S342), the calculated current value to be corrected is added to the current value used when the flash is turned on in the torch mode (S343). . The current value used in torch mode is always constant, so if only the current value needs to be corrected, the current value used in capture mode can be calculated.

Table 3 below shows the result of calculating the current value to be corrected from the actual torch mode driving current value and the current value to be actually driven in the capture mode using the correction constant calculated in Table 2.

[Table 3]

Distance (cm) Brightness of the subject (Y) Brightness correction value (Y) Current correction value (mA) Drive current value (mA) 10 153 -23 -92 208 30 109 21 84 384 60 53 77 308 608 100 7 123 492 792

 Here, the preset reference brightness was set to 130Y, and the brightness correction value was obtained from the difference from the brightness of the actual subject. The current compensation value is the value obtained by multiplying the compensation constant (4mA / Y) obtained before the brightness compensation value, and the drive current value is the current compensation value added to the current value 300mA in the torch mode.

Next, the image processor 220 sets the driving current value calculated in the flash driver IC 231 (S350).

The image processor 220 switches the torch mode to the capture mode after the operation is completed. In the capture mode, the flash is turned on according to the current value set in the flash driver IC 231 (S360), and the capture is performed (S370).

In the conventional LED flash control method, since the current value set in the flash driver IC 231 in the capture mode is constant, the amount of light of the flash 232 is also constant. However, according to the LED flash control method according to an embodiment of the present invention, in order to make the brightness of the subject equal to the preset reference brightness, the image processor 220 corrects the current value and sets it in the flash driver IC 231. Regardless of the distance from the flash to the subject, the optimum brightness of the subject can always be obtained.

In addition, according to the LED flash control method according to an embodiment of the present invention simply by programming the sequence of the above-described control method in the image processing unit 220 without adding a separate device such as a dimming sensor to simply optimize the brightness at a short distance You can get it.

It is intended that the invention not be limited by the foregoing embodiments and the accompanying drawings, but rather by the claims appended hereto. It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. something to do.

Figure 1 shows a flow chart of the LED flash control method according to the conventional method.

2 shows a schematic structure of a camera 200 including an LED flash.

Figure 3 shows a flow chart of the LED flash control method according to an embodiment of the present invention.

[Description of Major Symbols in Drawing]

200: camera with LED flash 210: back end

220: image processing unit 230: flash unit

231: flash driver IC 232: flash

Claims (7)

In the LED flash control method, (a) turning on the flash in a torch mode; (b) measuring the brightness of the subject in the torch mode; (c) calculating a current value required for a capture mode from the brightness of the subject measured in step (b); (d) setting the current value calculated in step (c) to a flash driver IC; and (e) turning on the flash in the capture mode according to the current value set in the flash driver IC in the step (d); Step (c) is, (c1) calculating brightness to be corrected from a difference between the brightness of the subject measured in step (b) and a preset reference brightness; (c2) calculating a current value to be corrected from brightness to be corrected calculated in step (c1); And (c3) adding the current value to be corrected calculated in step (c2) to the current value used in step (a). The method of claim 1, The LED flash control method includes an autofocusing step of moving the lens to the optimal focus position by finding the optimal focus position of the lens between the steps (a) and (b); LED flash control method further comprising. The method of claim 1, The LED flash control method includes an autofocusing step of moving the lens to the optimal focus position by finding the optimal focal position of the lens between the step (d) and the step (e); LED flash control method further comprising. 4. The method according to any one of claims 1 to 3, LED flash control method using a constant current value in the step (a). delete The method of claim 1, And the current value to be corrected in step (c2) is obtained by multiplying the brightness to be corrected by a preset correction constant. The method of claim 6, The preset correction constant is (I2-I1) / (B2-B1) (However, I1 and I2 are different current values set in the flash driver IC,  B1 is the brightness of the subject when the current value is I1, B2 is the brightness of the subject when the current value is I2) LED flash control method given by.

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