Camera2 Api Problems Firing Flash/no Flash Images

I will explain my case. I'm trying to do an application in which every 5 seconds will take an image, one without flash, and then after 5 seconds one with flash, and repeat this ev

Solution 1:

There are two levels of control for the flash - manual, and controlled by the auto-exposure routine. You're currently mixing them together.

If you want to fire the flash manually, then you need to set AE_MODE to either AE_MODE_OFF or AE_MODE_ON; not any of the FLASH modes. Then, FLASH_MODE will control whether the flash will be in torch mode, off, or fire once for a given request.

Since you're always leave AE_MODE in one of the FLASH states, what you do to FLASH_MODE should not matter, barring a bug in some specific device.

If you want to guarantee flash firing in every other picture, you need to use AE_MODE_ON_ALWAYS_FLASH for the force-flash photos, and you need to use AE_MODE_ON for the no-flash phoots; don't touch FLASH_MODE. Right now, with AUTO_FLASH, it's up to the device whether to fire a flash or not, so you'll see different behavior from different devices and lighting conditions - some will fire, some won't.

The other key thing you're not doing is running a precapture sequence; this is essential for flash pictures, because it allows the device to fire the preflash to determine correct flash power, focus, and white balance.

To run precapture, set the AE_MODE as desired, and then set AE_PRECAPTURE_TRIGGER to START for one request. This will transition AE_STATE to PRECAPTURE, and it'll stay there for some number of frames; once AE_STATE is no longer PRECAPTURE, you can issue the actual image capture request. Make sure you keep the AE_MODE consistent throughout this.

The sample app Camera2Basic implements the precapture sequence, so take a look there; it also has some optimizations that skip precapture in case the scene is not dark enough to need flash, but since you want to force-fire flash, that's not relevant to you.