Camera2 api problems firing flash/no flash images

Question

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 every time. So it will take one without flash, one with flash, one without flash, one with flash... infinitely.

The case is that with my code I can do this in some devices, but the same code won't work in others as I want. i.e:

BQ Aquaris X5 Plus : The no-flash image is correct, but the flash image will be just white.
BQ Aquaris E5 : Won't fire the flash.

How can this be possible, all devices in which I have tried are LEGACY hardware support level for Camera2 API.

This are some important methods in my code (I can't post all code due to char limit). I started from the Google Example:

This setAutoFlash does the mentioned above.

private void setAutoFlash(CaptureRequest.Builder requestBuilder) {
        if (mFlashSupported) {
            if(phototaken) {
                requestBuilder.set(CaptureRequest.CONTROL_AE_MODE,CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
                requestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF);
            }else{
                requestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_SINGLE);
            }
        }
    }

This other one works in some devices and the bq aquaris e5 but doesn't fire the flash in the bq aquaris x5 plus.

private void setAutoFlash(CaptureRequest.Builder requestBuilder) {
        if (mFlashSupported) {
            if(phototaken) {
                requestBuilder.set(CaptureRequest.CONTROL_AE_MODE,CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
                requestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF);
            }else{
                requestBuilder.set(CaptureRequest.CONTROL_AE_MODE,CaptureRequest.CONTROL_AE_MODE_ON_ALWAYS_FLASH);
                requestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF);
            }
        }
    }

And my captureStillPicture

private void captureStillPicture() {
        try {
            final Activity activity = getActivity();
            if (null == activity || null == mCameraDevice) {
                return;
            }
            // This is the CaptureRequest.Builder that we use to take a picture.
            final CaptureRequest.Builder captureBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
            captureBuilder.addTarget(mImageReader.getSurface());

            // Use the same AE and AF modes as the preview.
            captureBuilder.set(CaptureRequest.CONTROL_AF_MODE,
                    CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
            setAutoFlash(captureBuilder);

            // Orientation
            int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
            captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, getOrientation(rotation));

            CameraCaptureSession.CaptureCallback CaptureCallback
                    = new CameraCaptureSession.CaptureCallback() {
                @Override
                public void onCaptureCompleted(@NonNull CameraCaptureSession session,
                                               @NonNull CaptureRequest request,
                                               @NonNull TotalCaptureResult result) {
                    showToast("Saved: " + mFile);
                    Log.d(TAG, mFile.toString());
                    unlockFocus();
                }
            };

            mCaptureSession.stopRepeating();
            mCaptureSession.capture(captureBuilder.build(), CaptureCallback, null);
            phototaken = !phototaken;

        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
}

The question is, what am i doing wrong so it doesn't work in all devices? Any help will be great.

Eddy Talvala Eddy Talvala · Accepted Answer · 2017-03-28T21:34:18

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.

Camera2 api problems firing flash/no flash images

1 Answers