TWI584040B - Method for controlling flash timing of extension flash module - Google Patents

Description

Method for controlling flash time of external flash

The present invention relates to a flashlight technology, and more particularly to a method of photographing an external flash for a mobile device.

Due to advances in the quality and quality of digital photography, it has become a trend to have camera functions for mobile devices such as mobile phones and tablets. However, these built-in digital cameras have not been able to compete with traditional digital cameras in low-light or backlit environments.

Although some built-in digital cameras will also be equipped with LED (light-emitting diode) fill light, due to the battery capacity of the mobile device and the heat dissipation of the LED, the fill light of the LED fill light is severely limited. When the distance of the object is more than one meter, the LED cannot provide enough light source to make the photosensitive element properly exposed.

Xenon flash lamps can provide a large number of auxiliary light sources in a short period of time, so conventional digital cameras are often equipped with xenon flash lamps. Xenon flash lamps use a charging device to convert low-voltage battery power to high-voltage power and store it in high-capacity high-voltage capacitors. With the mechanical shutter, the xenon flash lamp is triggered at an appropriate time, and the electric energy stored in the high voltage capacitor is converted into a high-brightness auxiliary light source in a very short time, so that the photosensitive element is appropriately exposed in a low light source or a backlight environment. Xenon flash lamps require tens of uF to hundreds of uF and high-voltage capacitors with a withstand voltage of three to four hundred and four hundred volts. These capacitors are very large in size, and are not affordable for mobile devices under the premise that the mobile device is light and short. Therefore, the external xenon flash lamp becomes a viable and necessary option without increasing the size and weight of the mobile device.

According to the capacitance of the high-voltage capacitor and the specifications of the xenon lamp, the flash time of the xenon flash lamp is about several tens of microseconds to hundreds of microseconds. How to flash at the right time, so that all photosensitive elements can be evenly exposed is another important issue for the external xenon flash. The general action device is equipped with a photographic device that uses a CMOS sensor and is not equipped with a mechanical shutter, but uses a rolling shutter, as shown in Figure 1. Figure 1 is a schematic illustration of a prior art cyclic shutter. Referring to Fig. 1, in Fig. 1, each line represents the photosensitive time of each line of the photosensitive element. Although the exposure time of each column of photosensitive elements in a frame is the same, the start and end times of each column are separated from the previous column by a delay time. During this delay time, the camera reads the exposure information of the photosensitive element and completes the reset to perform exposure of the next frame. The exposure time of each column is approximately several milliseconds to hundreds of milliseconds, depending on the phase environment and the settings of the camera.

However, due to the limitation of the recirculating shutter, the external xenon flash often cannot find the best flash timing, and the quality of the photograph cannot be improved.

In one aspect, the present invention provides a method of controlling the flash time of an external flash, suitable for use when a mobile device is equipped with an external flash for photographic fill light, the method comprising: detecting a specific event prior to a flashable period Wherein the flashable period is the time from when a particular frame is exposed from the last column of photosensitive elements, to the time when the first column of photosensitive elements of the particular frame is exposed, wherein the time of occurrence of the particular event is relative to the The flashable period is a fixed length of time; and after a delay time from the particular event, a flash command is triggered to cause the flash time of the external flash to fall during the flashable period.

In one preferred embodiment, the delay time is determined based on a flash delay time and the time of the particular event to the flashable period.

In a preferred embodiment, the occurrence time of the specific event is t0, the time when the last column of the photosensitive element of the specific frame starts to be exposed is t1, and the exposure time of the first column of the photosensitive element of the specific frame is t2. The delay time is calculated as td1 from t0, and a trigger flash command is received from the external flash to the real flash, and there is a delay time td, wherein the start point of the delay time td is the time point at which the flash command is triggered), then: t1 -td-t0<td1<t2-td-t0.

In a preferred embodiment, the decision of the delay time comprises the steps of: (A) performing frame exposure according to a given delay time; (B) checking the exposed frame to compare the brightness of the photosensitive element with a Referring to the threshold comparison, and determining whether the brightness of the photosensitive element is lower than the reference threshold; (C1) when the brightness of the non-photosensitive element is lower than the reference threshold, the delay time of the exposure is the set delay time; (C2) when the brightness of the photosensitive element is lower than the reference threshold and the brightness of the photosensitive element that first receives the exposure is lower than the reference threshold, then the delay time is decreased, returning to step (A); and (C3) When the brightness of the photosensitive element is lower than the reference threshold and the brightness of the photosensitive element after receiving the exposure is lower than the reference threshold, the delay time is increased, and the process returns to step (A).

In a preferred embodiment, the brightness reference threshold is set by performing exposure without turning on the flash to obtain the lowest, highest, average, or specific position sensitivity of all of the photosensitive elements. The brightness of the component is the reference threshold.

In a preferred embodiment, the method for controlling the flash time of the external flash further comprises: lowering the reference threshold when the ambient light is dark, and increasing the reference threshold when the ambient light is brighter.

In one preferred embodiment, the delay time is preset to a driver of the external flash or an application installed by the mobile device.

In one preferred embodiment, the delay time is stored in a memory device included in the external flash.

In a preferred embodiment, the specific event includes: a time when one of the photosensitive elements of the specific frame starts to be exposed, or a time when one of the first N frames of the specific frame starts to be exposed, Or the time at which one of the photosensitive elements of the first N frames of the particular frame ends exposure, where N is a natural number.

In another aspect, the present invention provides a method for controlling the flash time of an external flash, which is suitable for when a mobile device is equipped with an external flash for photographic fill light, the method includes: sensing a time point when the mobile device emits light; And triggering a flashing command to cause the flashing time of the external flash to fall during the flashable period after the delay time of the lighting of the mobile device, wherein the flashing period is a specific frame from the last column of photosensitive elements The time at which the exposure starts, to the time when the exposure of the first column of photosensitive elements of the particular frame ends.

In a preferred embodiment, the time when the mobile device emits light includes: a time when the light-emitting diode fill light is built in the mobile device for the first time or the second time.

The spirit of the present invention is to utilize a specific event, the occurrence time of the specific event is relatively stable and known relative to the flashable time, and in conjunction with the delay time of controlling the flash, the flash is triggered to cause the flash to flash when it flashes. Inside. Therefore, with the photographing method of the present invention, the photosensitive member can be appropriately exposed in a low light source or a backlight environment, thereby achieving an effect of improving the photographic quality of the mobile device.

The purpose, technical content, features and effects achieved by the present invention will be more readily understood by the detailed description of the embodiments.

FIG. 2 is a schematic view showing a suitable flash time according to an embodiment of the present invention. Please refer to Figure 2, the time suitable for flash is only between t1 and t2. The flash during this time can be received by the photosensitive elements of each column. If the flash time is earlier than t1, the photosensitive elements in the rear column will not be exposed to light. If the flash time is later than t2, the photosensitive elements in the front row will not be exposed to light. However, the multi-tasking operation is usually performed by the mobile device, and the delay time for the user to press the shutter command to t1 or t2 is not fixed. Therefore, there is no feasible and reliable method to ensure that the flash time of the external flash can be stably controlled between t1 and t2, so that the use of the external xenon flash lamp is severely and fatally limited. Hereinafter, the present invention proposes a photographing method according to FIG. 2, so that the flash time of the external flash can be stably controlled between t1 and t2.

FIG. 3 is a flow chart of a photographing method according to a preferred embodiment of the present invention. Please refer to FIG. 3, which adopts a xenon flash lamp outside the mobile device to perform a fill light action when the mobile device is photographed. The photographing method includes the following steps:

Step S300: Start.

Step S301: detecting a specific event before a flashable period. Referring to FIG. 2, in general, the image capturing device used in the mobile device adopts the above-mentioned rolling shutter. Therefore, the photosensitive elements inside the mobile device are sequentially exposed one by one. Moreover, the manner in which each of the photosensitive elements inside the mobile device is exposed is integrated. Therefore, the flashable period is located between time t1 and time t2 of the particular frame captured as shown in FIG. As can be seen from Fig. 2, the time t1 and the time t2 are the time from the start of the exposure of the last column of photosensitive elements (initiation of integration) to the time when the exposure of the first column of photosensitive elements is completed (integration is completed). If you flash at this time, each scan line can be illuminated by integration.

After the mobile device confirms that the user presses the shutter command, the preparatory work including photometry, focusing, and the like is performed, and the exposure time of the specific frame and the photosensitive element to be captured is determined. At this time, the flashable sections t1 to t2 of the external flash device are known. For example, a designer can estimate the time of a particular frame by designing a particular application, or use other hardware signals to determine the time of that particular frame. Therefore, in this embodiment, the time at which a particular event occurs is used as a basis for the prediction. The time at which this particular event occurs is a fixed length of time relative to the flashable period described above, that is, a relatively stable and known time.

For example, in the implementation of a mobile device application (for example, a mobile application), the mobile application can capture the time when the first column of the specific frame of the specific frame starts to be exposed as the specific event. The fixed length of time is the length of time from the start of exposure of the first column of photosensitive elements to the start of exposure of the last column of photosensitive elements. The specific event may also be the time when the photosensitive element of the Kth column of the first N frames of the specific frame starts to be exposed. At this time, the fixed time length is N frames time plus, and the exposure is started from the Kth column photosensitive element. The time until the last column of exposure of the photosensitive element begins. The specific event may also be the time when the photosensitive element of the Kth column of the first N frames of the specific frame ends exposure. In this case, the fixed time length is the first N-1 frame time plus, from the Kth column. The length of time that the photosensitive element begins to be exposed until the exposure of the last column of photosensitive elements begins.

In the perspective of the external hardware, the specific event may be a signal of a light-emitting diode fill light built in the mobile device, and FIG. 4 illustrates an action taken by the photographing method according to a preferred embodiment of the present invention. The signal waveform of the built-in LED fill light. Please refer to Figure 4, when the mobile device is taking pictures, the built-in LED fill light will indicate that the lens is in focus for the first time, and the built-in LED fill light will indicate the second time. Take the action of the picture (photosensitive). Therefore, in step S301 of the present invention, the specific event may be the first illumination of the light-emitting diode fill light or the second illumination of the light-emitting diode fill light.

Step S302: trigger a flash command according to a flash delay time and the time of the specific event to the flashable period, so that the flash time of the external flash falls within the flashable period. The flash itself has a delay from the receipt of the trigger flash command to the actual flash. Therefore, in addition to the time during which the above specific events are considered to be flashable, the delay time of the flash itself should also be considered. In short, since the time from the above specific event to the flashable period is a fixed value, and the delay time of the flash itself is a known value, it can be determined accordingly when the flash command is triggered. For example, if the delay time from the receipt of the trigger flash command to the real flash is td (ie, the reference start point of the delay time td is the time point at which the flash command is triggered), the time for triggering the flash command can be t1-td to t2- Between td. Or, if the reference start point of the delay time td is from the time of the specific event, and the occurrence time of the specific event is t0, the flash time needs to satisfy the relationship t1-t0 < td < t2-t0, at td The external flash unit flashes when it is finished. If the difference between the start point of the delay time td and the time of the above specific event is calculated, the difference can be taken into account, depending on the definition of the delay time td.

The aforementioned external flash is connected by hardware, electrically connected via a universal serial bus bar equipped with a mobile device, or electrically coupled via a headphone jack equipped with a mobile device, and cooperates with the internal software of the mobile device to determine a specific event, such as starting a photosensitive device. Time or illuminating diodes illuminate the signal for flashing techniques. However, in accordance with the spirit of the present invention, an embodiment of optical coupling may also be employed. FIG. 5 is a block diagram of a system for using an external flash for a photographing method according to an embodiment of the present invention. Please refer to FIG. 5, in addition to the hanging flash 50, for example, an external flash that is in contact with the mobile device. In addition, the hanging flash 50 includes a light sensing circuit 501, a delay circuit 502, a flash driving circuit 503, and a xenon lamp 504. The light-emitting diode fill light is sensed by the light-sensing circuit sensing mobile device 51 as the above-described specific event, whereby the xenon lamp 504 is driven to flash at the flash time (t1 to t2).

In addition, although the above embodiments are implemented in an optical coupling manner, those skilled in the art should know that the present invention can also adopt wireless, such as WIFI, Near Field Communication (NFC) or Bluetooth. The mode and the mobile device emit a shutter sound to perform coupling. Therefore, the invention is not limited thereto.

Furthermore, in general, the time during which the above-mentioned specific events occur is a fixed length of time relative to the above-described flashable period, that is, a relatively stable and known time. However, the designer cannot guarantee that the above-mentioned several events have no error. However, the present invention is only required that the time of occurrence of the above specific events is less than an allowable range with respect to the time error of the above-mentioned flashable period, for example, during the flashable period. Within one-half, it is within the acceptable range of the present invention.

In addition, with the flash as the external hardware, the external flash must be able to match the different types of mobile devices. Although for a single mobile device, the time between the above-mentioned specific events and the above-mentioned flashable period is a fixed value, the fixed value may be different for different brand-type mobile devices. In an embodiment, when the fixed value of some of the brand-type mobile devices is known, different known fixed values may be preset in advance to the driver of the external flash or an application installed by the mobile device. Within the program. Referring to FIG. 6, for example, when the mobile device is equipped with an external flash, an application may be installed. After the application identifies the brand type or related attributes of the mobile device, the delay time td1 of the delay circuit 502 is determined. Referring to the foregoing, from the flash to receive the trigger flash command to the real flash, there will be a delay time td (where the reference start point of the delay time td is the time point at which the flash command is triggered), so the delay time td1 of the delay circuit 502 should be controlled. So that the time to trigger the flash command can be between t1-td and t2-td. Assuming that the occurrence time of the above specific event is t0, and the delay time td1 is also calculated from t0, then t1-td-t0<td1<t2-td-t0.

In another embodiment, different known fixed values can be stored within the hardware circuitry. Referring to FIG. 7 and FIG. 8 , in the embodiment, first, at least one mobile device, the time constant value from the time when a specific event occurs to the flashable period is stored in the external flash 50. In the memory device (memory 505) (step S801). When the camera is to be photographed, the external flash unit 50 communicates with the mobile device to obtain the brand type or related attribute of the mobile device (step S802), and determines the delay time td1 with reference to the time constant value stored in the memory device (step S803). The occurrence of the specific event is then detected (step S804). After the occurrence of the specific event, the time td1 is delayed, and then a flash command is triggered (step S805).

In another embodiment, please refer to Fig. 9. When the fixed value of some of the brand-type mobile devices is unknown, a detection procedure can be used to obtain a better delay time. In this embodiment, first, for example, but not limited to, when the mobile device is connected to the external flash for the first time, or when the driver of the external flash is installed, or at another suitable time, a test shooting process is started (step S901). ). In the test shooting procedure, the mobile device is equipped with an external flash to perform frame exposure according to a given delay time (step S902). Next, the exposed frame is inspected, the brightness of the photosensitive element is compared with a reference threshold (step S903), and it is judged whether or not the brightness of the photosensitive element is lower than the reference critical value (step S904). If not, the delay time of the exposure is the set delay time (step S905). If there is, and the brightness of the photosensitive element (the first column or the first few columns of FIG. 1) that first receives the exposure is lower than the reference threshold (steps S906, S907), the delay time is reduced (the time for triggering the flash command is advanced) (Step S908), return to step S902. If there is, and the brightness of the photosensitive element (the Nth column or the following columns of FIG. 1) after receiving the exposure is lower than the reference threshold (steps S906, S909), the delay time is increased (the time delay of triggering the flash command is increased) Thereafter (step S910), the process returns to step S902. In this way, you can find the appropriate delay time.

In order to avoid misjudgment, it can be considered that the delay time must be adjusted if the brightness of the photosensitive element that must exceed a certain critical number is lower than the reference threshold.

In addition, in an embodiment, the setting manner of the brightness reference threshold value, for example, but not limited to, may be: performing exposure without turning on the flash to obtain the brightness (the lowest brightness, the highest, and the highest brightness of all the photosensitive elements) The average value, or the brightness of the photosensitive element at a particular location, such as center, perimeter, or corner, is the reference threshold.

In an embodiment, the setting of the reference threshold can be adjusted according to the detection of ambient light. For example, if the mobile device is provided with an ambient light detector, the reference threshold may be lowered correspondingly when the ambient light is dark according to the detected value of the ambient light, and increased when the ambient light is brighter. Refer to the threshold.

In summary, the spirit of the present invention is to utilize a specific event, the occurrence time of the specific event is relatively stable and known relative to the flashable time, and when the delay time of the flash is controlled, the flash is triggered to cause the flash to flash. Fall in the flash time. Therefore, with the photographing method of the present invention, the photosensitive member can be appropriately exposed in a low light source or a backlight environment, thereby achieving an effect of improving the photographic quality of the mobile device.

The specific embodiments of the present invention are intended to be illustrative only and not to limit the invention to the above embodiments, without departing from the spirit of the invention and the following claims. The scope of the invention and the various changes made are within the scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

S300～S302‧‧‧Steps
S800 ~ S805‧‧‧ steps
S900～S910‧‧‧Steps
50‧‧‧External flash
501‧‧‧Light sensing circuit
502‧‧‧Delay circuit
503‧‧‧Flash drive circuit
504‧‧‧Xenon lights
505‧‧‧ memory
51‧‧‧Mobile devices

1 is a schematic diagram of a prior art cyclic shutter; FIG. 2 is a schematic diagram of a suitable flashing time according to an embodiment of the present invention; FIG. 3 is a flow chart of a photographing method according to a preferred embodiment of the present invention; A signal waveform diagram of a light-emitting diode fill light built in a mobile device used in a photographing method according to a preferred embodiment of the present invention; FIG. 5 is a system block diagram of an external flash using a photographing method according to an embodiment of the present invention; Figure 6 shows another embodiment in accordance with the present invention; Figures 7 and 8 show still another embodiment in accordance with the present invention; and Figure 9 shows still another embodiment in accordance with the present invention.

S900-S910‧‧‧Steps

Claims (16)

A method for controlling flash time of an external flash lamp, suitable for when a mobile device is equipped with an external flash for photographic fill light, the method comprising: detecting a specific event before a flashable period, wherein the flashable period is a specific The time from the start of exposure of the last column of photosensitive elements to the end of exposure of the first column of photosensitive elements of the particular frame, wherein the particular event occurs for a fixed length of time relative to the flashable period; The message of the specific event is notified to the external flash so that the external flash triggers a flash command after the delay time of the specific event, so that the flash time of the external flash falls during the flashable period. The method for controlling the flash time of the plug-in flash as recited in claim 1, wherein the delay time is determined according to a flash delay time and a time of the specific event to the flashable period. The method for controlling the flash time of the external flash as described in claim 2, wherein the occurrence time of the specific event is t0, and the exposure time of the last column of the specific frame of the specific frame is t1, the specific frame The end of exposure of a column of photosensitive elements is t2, the delay time is calculated as td1 from t0, and a flashing command is received from the external flash to the real flash, there is a delay time td, wherein the starting point of the delay time td is a trigger At the time point of the flash command, then: t1-td-t0<td1<t2-td-t0. The method for controlling the flash time of the external flash as described in the first aspect of the patent application, wherein the determining of the delay time comprises the following steps: (A) performing frame exposure according to a given delay time; (B) checking the exposure after exposure a frame, comparing the brightness of the photosensitive element with a reference threshold, and determining whether the brightness of the photosensitive element is lower than the reference threshold; (C1) When the brightness of the non-photosensitive element is lower than the reference threshold, the delay time of the exposure is the set delay time; (C2) when the brightness of the photosensitive element is lower than the reference threshold, and is accepted first When the brightness of the exposed photosensitive element is lower than the reference threshold, the delay time is reduced, and the process returns to step (A); and (C3) when the brightness of the photosensitive element is lower than the reference threshold, and the photosensitive element is exposed after exposure. When the brightness is lower than the reference threshold, the delay time is increased and the process returns to step (A). The method for controlling the flash time of the external flash as described in claim 4, wherein the brightness reference threshold is set by performing exposure without turning on the flash, so that the lowest brightness of all the photosensitive elements is obtained. The highest, average, or brightness of the photosensitive element at a particular location is the reference threshold. The method for controlling the flash time of the external flash as described in claim 4 of the patent application further includes: lowering the reference threshold when the ambient light is dark, and increasing the reference threshold when the ambient light is bright. The method for controlling the flash time of the external flash as described in the first aspect of the patent application, wherein the delay time is preset in a driver of the external flash or an application installed in the mobile device. The method for controlling the flash time of the external flash as described in the first aspect of the patent application, wherein the delay time is stored in a memory device included in the external flash. The method for controlling the flash time of the external flash as described in the first aspect of the patent application, wherein the specific event comprises: a time when one of the photosensitive elements of the specific frame starts to be exposed, or the first N frames of the specific frame The time at which one of the columns of photosensitive elements begins to be exposed, or the time at which one of the columns of the first N frames of the particular frame ends exposure, where N is a natural number. A method for controlling flash time of an external flash lamp, wherein when a mobile device is equipped with an external flash for photographic fill light, the method includes: sensing a time point when the mobile device emits light; and starting a time when the mobile device emits light After the delay time, a flash command is triggered to cause the flash time of the external flash to fall during a flashable period, wherein the flashable period is when a particular frame is exposed from the last column of photosensitive elements, to the specific frame The time at which the exposure of the first column of photosensitive elements ends. The method for controlling the flash time of the external flash as described in claim 10, wherein the mobile device emits light at the time of: the mobile device has a built-in light-emitting diode fill light for the first time or the second time. The time of illumination. The method for controlling the flash time of the external flash as described in claim 10, wherein the decision of the delay time comprises the following steps: (A) performing frame exposure according to a given delay time; (B) checking the exposure after exposure. a frame, comparing the brightness of the photosensitive element with a reference threshold, and determining whether the brightness of the photosensitive element is lower than the reference threshold; (C1) when the brightness of the non-photosensitive element is lower than the reference threshold, The delay time of the exposure is the set delay time; (C2) when the brightness of the photosensitive element is lower than the reference threshold, and the brightness of the photosensitive element that first receives the exposure is lower than the reference threshold, the delay time is reduced, and the delay is returned. Step (A); and (C3) when the brightness of the photosensitive element is lower than the reference threshold and the brightness of the photosensitive element after receiving the exposure is lower than the reference threshold, the delay time is increased, and the step (A) is returned. . The method for controlling the flash time of the external flash as described in claim 12, wherein the brightness reference threshold is set by: not opening the flash The exposure is determined by the lowest brightness, the highest, the average value, or the brightness of the photosensitive member at a specific position of all the photosensitive elements obtained. The method for controlling the flash time of the external flash as described in claim 12 of the patent application further includes: lowering the reference threshold when the ambient light is dark, and increasing the reference threshold when the ambient light is brighter. The method for controlling the flash time of the external flash as described in claim 10, wherein the delay time is preset in a driver of the external flash or an application installed in the mobile device. The method for controlling the flash time of the external flash as described in claim 10, wherein the delay time is stored in a memory device included in the external flash.