How to ensure focused before taking picture in Android CameraX? (Should be a very commonly used feature!)

Question

I am using CameraX and want to take a photo. Of course, no one wants a blurred picture, so we should ensure focused before taking picture.

First attempt: Simply call takePicture like what is done in the official sample.

Problem: I can change the scene and quickly press the take photo button. Then, the camera has not finished auto focus when the takePicture happens. Therefore, I get a blurred photo :/

Second attempt: Before actually taking photo, firstly trigger focusing and wait for it to finish.

Code like:

camera!!.cameraControl.startFocusAndMetering(
                    FocusMeteringAction.Builder(
                            autoFocusPoint,
                            FocusMeteringAction.FLAG_AF
                    ).apply {
                        //focus only when the user tap the preview
                        disableAutoCancel()
                    }.build()
            )

Problem: It takes so long to do a focus (seconds!). Users definitely cannot accept that.

Therefore, I wonder what should I do? IMHO this should be very commonly used, so I am surprised to see that I cannot find any solution! Do I miss something?

Thanks for any suggestions!

Answer 1

I found the answer! Simply call setCaptureMode(ImageCapture.CAPTURE_MODE_MAXIMIZE_QUALITY).

Reason: look at ImageCapture's constructor:

        if (mCaptureMode == CAPTURE_MODE_MAXIMIZE_QUALITY) {
            mEnableCheck3AConverged = true; // check 3A convergence in MAX_QUALITY mode
        } else {
            mEnableCheck3AConverged = false; // skip 3A convergence in MIN_LATENCY mode
        }

And that field:

    /**
     * A flag to check 3A converged or not.
     *
     * <p>In order to speed up the taking picture process, trigger AF / AE should be skipped when
     * the flag is disabled. Set it to be enabled in the maximum quality mode and disabled in the
     * minimum latency mode.
     */
    private final boolean mEnableCheck3AConverged;

Aha!