如何为视频录制指定曝光,对焦和白平衡？

Question

我有一个程序来拍摄带有默认参数的视频,当我移动相机时,将自动调整曝光,聚焦和白平衡.我想在程序中添加2个按钮:LOCK和PRESET.按下LOCK按钮时,曝光,对焦和白平衡将被修复,其值将作为用户设置存储.PRESET按钮用于将用户设置设置为相机,以确保我们可以拍摄具有相同曝光,对焦和白平衡值的所有视频.

锁定部分很简单,我只需要改变模式,所以我想知道是否有任何方法可以获得并设置曝光,聚焦和白平衡的值.

以曝光为例,默认情况下,曝光模式设置为AVCaptureExposureModeContinuousAutoExposure,这意味着,当我拿着iPhone拍摄视频时,曝光将自动调整,以确保我们可以在明亮或黑暗的环境中清晰地看到场景.

AVCaptureDevice* pCaptureDevice = [self videoDeviceWithPosition:AVCaptureDevicePositionBack];
[pCaptureDevice lockForConfiguration:nil];
[pCaptureDevice setExposureMode:AVCaptureExposureModeContinuousAutoExposure];
[pCaptureDevice unlockForConfiguration];

按下LOCK按钮时,我将exposureMode更改为AVCaptureExposureModeLocked,因此不再更改当前曝光值.

[pCaptureDevice lockForConfiguration:nil];
[pCaptureDevice setExposureMode:AVCaptureExposureModeLocked];
[pCaptureDevice unlockForConfiguration];

但是,如何在按下按钮时获取曝光值？更重要的是,当按下PRESET时,如何将曝光值设置回AVCaptureDevice.

我在论坛中搜索过,只发现了Michael Grinich的帖子:访问iOS 6新的API,用于相机曝光和快门速度.我按照他的发现并尝试使用私有API获取并设置exposureGain和exposureDuration,但我发现在AVCaptureExposureModeContinuousAutoExposure模式下,当我将相机从黑暗环境移动到明亮时(曝光增益= 1.0和exposureDuration = {1,30,1,0}).设置它们并没有改变曝光度.

[pCaptureDevice lockForConfiguration:nil];
[pCaptureDevice setExposureMode:AVCaptureExposureModeLocked];
[pCaptureDevice setManualExposureSupportEnabled:YES];
NSLog(@"exposure gain: %f", [pCaptureDevice exposureGain]);
[pCaptureDevice setExposureGain:3.0];
NSLog(@"exposure gain: %f", [pCaptureDevice exposureGain]);
[pCaptureDevice unlockForConfiguration];

有人可以帮我解决这个问题吗？首先十分感谢!

Answer 1

我添加了一个答案，可能会帮助您访问 iOS 6 新的相机曝光和快门速度 API。我可以在这里添加更多细节......

手动设置焦点遵循与我概述的设置曝光完全相同的结构。那是：

#define AVCaptureFocusModeManual     3
NSError*    error = nil;
if ([captureDevice lockForConfiguration:&error]) {
    captureDevice.manualFocusSupportEnabled = YES;
    if ([captureDevice isFocusModeSupported:AVCaptureFocusModeManual]) {
        captureDevice.focusMode = AVCaptureFocusModeManual;
        // this is a value [0..1]
        captureDevice.focusPosition = ...;
    }
    [captureDevice unlockForConfiguration];
}

白平衡似乎没有像曝光和对焦那样有特殊的模式。不要将 WhiteBalanceMode 设置为锁定，否则似乎您可以只设置色温：

// this is also a value [0..1]
captureDevice.whiteBalanceTemperature = ...;