Question

我正在尝试在循环中使用captureStillImageAsynchronouslyFromConnection捕捉连续（多次拍摄）高分辨率图像，但偶尔会暂停重新对焦。我锁定了对焦模式（如其他stackoverflow贴图中所述），但这并没有阻止相机偶尔重新对焦。我的代码段是：

// [self.session beginConfiguration];
if ([device lockForConfiguration:nil] == YES) {
    if ([device isFocusModeSupported:AVCaptureFocusModeLocked]) {
        [device setFocusMode:AVCaptureFocusModeLocked];
        NSLog(@"focus locked");
    }
    if ([device isExposureModeSupported:AVCaptureExposureModeLocked]) {
        [device setExposureMode:AVCaptureExposureModeLocked];
        NSLog(@"exposure locked");
    }
    if ([device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeLocked]) {
        [device setWhiteBalanceMode:AVCaptureWhiteBalanceModeLocked];
        NSLog(@"white balance locked");
    }
}
// [self.session commitConfiguration];

for (int n = 0; n < 5; n++) {
    [self.stillImageOutput captureStillImageAsynchronouslyFromConnection:[self.stillImageOutput connectionWithMediaType:AVMediaTypeVideo] completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) {

        if (imageDataSampleBuffer) {
            NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
            UIImage *image = [[UIImage alloc] initWithData:imageData];
            [[[ALAssetsLibrary alloc] init] writeImageToSavedPhotosAlbum:[image CGImage] orientation:(ALAssetOrientation)image.imageOrientation completionBlock:nil];
        }
    }];
}

[device unlockForConfiguration]

输出日志报告：

focus locked
exposure locked
white balance locked

表示focus等人应该已成功锁定。

我尝试使用[device unlockForConfiguration]和[device unlockForConfiguration]包装锁码，但这并没有解决问题。

有人可以识别我的代码中的错误或我错过的一个步骤吗？（我意识到我可以使用视频捕获而不是仍然捕获来实现这一点，但我需要AVCaptureSessionPresetPhoto分辨率图像。）任何帮助将不胜感激。谢谢。

Answer 1

好的，我发现了问题。由于线程和GCD任务的时间安排，所有[device unlockForConfiguration]调用完成之前captureStillImageAsynchronouslyFromConnection正在执行。一个快速的解决方案是添加一个自旋锁，例如：

if ([device lockForConfiguration:nil]) {
    if ([device isFocusModeSupported:AVCaptureFocusModeLocked])
        [device setFocusMode:AVCaptureFocusModeLocked];
    if ([device isExposureModeSupported:AVCaptureExposureModeLocked])
        [device setExposureMode:AVCaptureExposureModeLocked];
    if ([device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeLocked])
        [device setWhiteBalanceMode:AVCaptureWhiteBalanceModeLocked];
}

__block int photoCount = 5; 
for (int n = photoCount; n > 0; n--) {
    [self.stillImageOutput captureStillImageAsynchronouslyFromConnection:[self.stillImageOutput connectionWithMediaType:AVMediaTypeVideo] completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) {
        @synchronize(self) {
            photoCount--;
        }

        if (imageDataSampleBuffer) {
            NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
            UIImage *image = [[UIImage alloc] initWithData:imageData];
            [[[ALAssetsLibrary alloc] init] writeImageToSavedPhotosAlbum:[image CGImage] orientation:(ALAssetOrientation)image.imageOrientation completionBlock:nil];
        }
    }];
}

while (photoCount > 0); // Spinlock until captureStillImageAsynchronouslyFromConnection captured all photos into memory
[device unlockForConfiguration]

那里可能有更多优雅的解决方案（我很乐意听到它们），但是一个简单的自旋锁就可以了。（此外，由于我的代码在dispatch_async块中运行，因此它不会导致UI或应用程序响应性出现任何问题。）

如何使用captureStillImageAsynchronouslyFromConnection实现多次拍摄（iOS AVFoundation）

1 个答案: