Question

I am trying to make auto focus work in my app, tested in iPad2. My problem is that when I called check methods like isFocusModeSupported:AVCaptureFocusModeContinuousAutoFocus, it always return NO. However, I could tap to focus with other camera applications in my device

devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
for (AVCaptureDevice *tempDevice in devices) {
    [tempDevice lockForConfiguration:nil];
    if ([tempDevice isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {
        NSLog(@"Here");
    }

    if ([tempDevice isFocusModeSupported:AVCaptureFocusModeContinuousAutoFocus]) {
        NSLog(@"Here");
    }

    if ([tempDevice isFocusModeSupported:AVCaptureFocusModeLocked]) {
        NSLog(@"Here");
    }

    if ([tempDevice isFocusPointOfInterestSupported]) {
        NSLog(@"Here");
    }
    [tempDevice unlockForConfiguration];
}

Answer 1

I was just looking into this tonight. From what I have gleaned, the iPad 2 doesn’t do focus – it does exposure adjustment – so in the default Camera app, tapping the screen brings up a rect where the tap occurred indicating the area to do white point adjustment on.

Perhaps I am wrong but this is what I have turned up, and seems to be confirmed by your API (isFocusModeSupported:AVCaptureFocusModeContinuousAutoFocus returning NO) tests.

The cameras in the iPad 2 are pretty weak – especially the front-facing one. I am surprised Apple shipped with that.

UPDATE: This is the code from the more recent AVCamDemo Apple sample that handles focus + exposure + white point. I don’t think this is in the AVCam example. AVCamDemo may onlly be available as a download of the WWDC code .dmg package from the developer center – not as a single download from the web.
On my iPad 2 the exposure code never gets called.
//-from AVCamDemo:

- (BOOL) hasExposure
 {
AVCaptureDevice *device = [[self videoInput] device];

return  [device isExposureModeSupported:AVCaptureExposureModeLocked] ||
        [device isExposureModeSupported:AVCaptureExposureModeAutoExpose] ||
        [device isExposureModeSupported:AVCaptureExposureModeContinuousAutoExposure];
}

- (AVCaptureExposureMode) exposureMode
{
return [[[self videoInput] device] exposureMode];
}

- (void) setExposureMode:(AVCaptureExposureMode)exposureMode
{
if (exposureMode == 1) {
    exposureMode = 2;
}
AVCaptureDevice *device = [[self videoInput] device];
if ([device isExposureModeSupported:exposureMode] && [device exposureMode] != exposureMode) {
    NSError *error;
    if ([device lockForConfiguration:&error]) {
        [device setExposureMode:exposureMode];
        [device unlockForConfiguration];
    } else {
        id delegate = [self delegate];
        if ([delegate respondsToSelector:@selector(acquiringDeviceLockFailedWithError:)]) {
            [delegate acquiringDeviceLockFailedWithError:error];
        }
    }
}
}

- (BOOL) hasWhiteBalance
{
AVCaptureDevice *device = [[self videoInput] device];

return  [device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeLocked] ||
        [device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeAutoWhiteBalance];
}

- (AVCaptureWhiteBalanceMode) whiteBalanceMode
{
return [[[self videoInput] device] whiteBalanceMode];
}

- (void) setWhiteBalanceMode:(AVCaptureWhiteBalanceMode)whiteBalanceMode
{
if (whiteBalanceMode == 1) {
    whiteBalanceMode = 2;
}    
AVCaptureDevice *device = [[self videoInput] device];
if ([device isWhiteBalanceModeSupported:whiteBalanceMode] && [device whiteBalanceMode] != whiteBalanceMode) {
    NSError *error;
    if ([device lockForConfiguration:&error]) {
        [device setWhiteBalanceMode:whiteBalanceMode];
        [device unlockForConfiguration];
    } else {
        id delegate = [self delegate];
        if ([delegate respondsToSelector:@selector(acquiringDeviceLockFailedWithError:)]) {
            [delegate acquiringDeviceLockFailedWithError:error];
        }
    }
}
}

- (BOOL) hasFocus
{
AVCaptureDevice *device = [[self videoInput] device];

return  [device isFocusModeSupported:AVCaptureFocusModeLocked] ||
        [device isFocusModeSupported:AVCaptureFocusModeAutoFocus] ||
        [device isFocusModeSupported:AVCaptureFocusModeContinuousAutoFocus];
}

- (AVCaptureFocusMode) focusMode
{
return [[[self videoInput] device] focusMode];
}

- (void) setFocusMode:(AVCaptureFocusMode)focusMode
{


AVCaptureDevice *device = [[self videoInput] device];
if ([device isFocusModeSupported:focusMode] && [device focusMode] != focusMode) {
    NSError *error;

      printf(" setFocusMode    \n");
    if ([device lockForConfiguration:&error]) {
        [device setFocusMode:focusMode];
        [device unlockForConfiguration];
    } else {
        id delegate = [self delegate];
        if ([delegate respondsToSelector:@selector(acquiringDeviceLockFailedWithError:)]) {
            [delegate acquiringDeviceLockFailedWithError:error];
        }
    }    
}
}