Method for controlling flash timing of extension flash module

1. A method for controlling flash timing of an extension flash module cooperating with a mobile device to provide supplemental light when the mobile device having an image retrieval device is taking a photo, the image retrieval device including pixels arranged in rows, the method comprising:

detecting a specific event before a flashable time period, wherein the flashable time period is a period from the time at which a last row in a specific frame begins exposure to the time at which a first row in the specific frame ends exposure, wherein the time period from when the specific event occurs to a flashable time in the flashable time period has a fixed length of time; and

informing the extension flash module the occurrence of the specific event, so that the extension flash module triggers a flash instruction after a delay time from when the specific event occurs, such that the flash timing of the extension flash module is in the flashable time period;

wherein the delay time is determined by steps including:

(A) exposing a frame according to a given delay time;

(B) checking the exposed frame and comparing brightnesses of the pixels with a reference threshold, to determine whether a pixel has a brightness lower than the reference threshold;

(C1) when none of the pixels has a brightness lower than the reference threshold, setting the given delay time as a default delay time;

(C2) when one or more of the pixels have a brightness lower than the reference threshold, and the pixel having brightness lower than the reference threshold is exposed earlier than half of the other pixels, shortening the delay time; and

(C3) when one or more of the pixels have a brightness lower than the reference threshold, and the pixel having brightness lower than the reference threshold is exposed later than half of the other pixels, prolonging the delay time.

2. The method of claim 1 , wherein the delay time is determined according to a flash delay time and the time period from when the specific event occurs to the flashable time in the flashable time period, wherein the flash delay time is a period from the time at which the extension flash module starts to execute the flash instruction to the time at which the extension flash module actually flashes.

3. The method of claim 2 , wherein the time at which the specific event occurs is t 0 , the time at which the last row in the specific frame begins exposure is t 1 , and the time at which the first row in the specific frame ends exposure is t 2 , and wherein the delay time which begins at t 0 has a duration of td 1 , and the flash delay time has a duration of td, wherein an initial time point of the duration of td is the time at which the extension flash module starts to execute the flash instruction, then the following relationship is fulfilled: (t 1 −td−t 0 )<td 1 <(t 2 −td−t 0 ).

4. The method of claim 1 , wherein the reference threshold of brightness is set by steps including:

performing an exposure without flashing the extension flash module; and

taking a lowest, highest, or average brightness among all pixels, or a brightness of a pixel at a predetermined position, as the reference threshold.

5. The method of claim 1 , further comprising:

lowering the reference threshold when an ambient light is relatively dimmer, and raising the reference threshold when the ambient light is relatively brighter.

6. The method of claim 1 , wherein the delay time is pre-stored in a driver program of the extension flash module or an application program of the mobile device.

7. The method of claim 1 , wherein the delay time is stored in a memory device included in the extension flash module.

8. The method of claim 1 , wherein the specific event includes:

the time at which one of the rows of the pixels in the specific frame begins exposure;

the time at which one of the rows of the pixels in the previous Nth frame prior to the specific frame begins exposure; or

the time at which one of the rows of the pixels in the previous Nth frame prior to the specific frame ends exposure;

wherein N is a natural number.

9. A method for controlling flash timing of an extension flash module cooperating with a mobile device to provide supplemental light when the mobile device having an image retrieval device is taking a photo, the image retrieval device including pixels arranged in rows, the method comprising:

sensing a light emitting time point at which the mobile device emits light; and

triggering a flash instruction after a delay time from the light emitting time point at which the mobile device emits light, such that the flash timing of the extension flash module is in a flashable time period;

wherein the flashable time period is a period from the time at which a last row in a specific frame begins exposure to the time at which a first row in the specific frame ends exposure

wherein the delay time is determined by steps including:

(A) exposing a frame according to a given delay time;

(B) checking the exposed frame and comparing brightnesses of the pixels with a reference threshold, to determine whether a pixel has a brightness lower than the reference threshold;

(C1) when none of the pixels has a brightness lower than the reference threshold, setting the given delay time as a default delay time;

(C2) when one or more of the pixels have a brightness lower than the reference threshold, and the pixel having brightness lower than the reference threshold is exposed earlier than half of the other pixels, shortening the delay time; and

(C3) when one or more of the pixels have a brightness lower than the reference threshold, and the pixel having brightness lower than the reference threshold is exposed later than half of the other pixels, prolonging the delay time.

10. The method of claim 9 , wherein the light emitting time point is: a time point at which a built-in light emitting diode (LED) supplement lamp of the mobile device begins to emit light for the first time or a time point at which the built-in LED supplement lamp begins to emit light for the second time.

11. The method of claim 9 , wherein the reference threshold of brightness is set by steps including:

performing an exposure without flashing the extension flash module; and

taking a lowest, highest, or average brightness among all pixels, or a brightness of a pixel at a predetermined position, as the reference threshold.

12. The method of claim 9 , further comprising:

lowering the reference threshold when an ambient light is relatively dimmer, and raising the reference threshold when the ambient light is relatively brighter.

13. The method of claim 9 , wherein the delay time is pre-stored in a driver program of the extension flash module or an application program of the mobile device.

14. The method of claim 9 , wherein the delay time is stored in a memory device included in the extension flash module.