AVFoundation:isExposureModeSupported为AVCaptureExposureModeAutoExpose返回FALSE

Question

我正在使用AVFoundation构建自定义相机.除了之外,一切都很好setExposurePointOfInterest.

我在iPhone 5上测试,AVCaptureDevice告诉我BackCamera不支持AVCaptureExposureModeAutoExpose.

然后我如何实施水龙头来调整曝光？

这是我的代码:

- (void)didTapCameraPreview:(UITapGestureRecognizer *)recognizer {

CGPoint point = [recognizer locationInView:self.view];
CGRect screenRect = [self.view bounds];
CGFloat screenWidth = screenRect.size.width;
CGFloat screenHeight = screenRect.size.height;
double focus_x = point.x/screenWidth;
double focus_y = point.y/screenHeight;

CGPoint touchPoint = CGPointMake(focus_x, focus_y);

AVCaptureDevice *device = (self.captureSession.inputs[0] == self.backCamera) ? self.backCamera.device : self.frontCamera.device;

if (device.isFocusPointOfInterestSupported) {
    NSError *error;
    if ([device lockForConfiguration:&error]) {
        [device setFocusPointOfInterest:touchPoint];
        [device setExposurePointOfInterest:touchPoint];

        [device setFocusMode:AVCaptureFocusModeAutoFocus];
        if ([device isExposureModeSupported:AVCaptureExposureModeAutoExpose]){
            [device setExposureMode:AVCaptureExposureModeAutoExpose];
        }
        [device unlockForConfiguration];
    }
}

}

Answer 1

我在 Apple 开发者论坛中提出了类似的问题，并得到了 Brad Ford（核心媒体工程）的回答，他是 Apple WWDC 中 Camera Capture with AV Foundation 的发言人。

这是他的回答：

正确的。AVCaptureExposureModeAutoExpose 虽然在标头中定义，但目前尚未在任何 iOS 设备上实现。

但是，您可以在自己的代码中实现它，方法是设置所需的兴趣点，然后调用 setExposureMode:AVCaptureExposureModeContinouslyAutoExposure，然后监听（键值观察）AVCaptureDevice 的“isAdjustingExposure”属性以了解曝光何时完成调整。一旦完成，将ExposureMode 设置为AVCaptureExposureModeLocked。

希望它能澄清并有所帮助！