iOS 相机管理

iOS 相机管理是指在 iOS 应用程序中使用相机的管理和调用。iOS 相机管理可以实现应用程序中的图片或者视频拍摄、图像处理，以及直接调用系统相机进行拍照等操作。本篇文章将介绍如何在 iOS 应用程序中进行相机管理。

1. 调用系统相机

在 iOS 应用程序中，我们可以通过调用系统相机实现拍照和录制视频。具体方法如下：

if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
    UIImagePickerController *imagePicker = [[UIImagePickerController alloc] init];
    imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
    imagePicker.allowsEditing = YES;
    imagePicker.delegate = self;
    [self presentViewController:imagePicker animated:YES completion:nil];
} else {
    NSLog(@"相机不可用");
}

上述代码的作用是判断当前设备是否支持调用相机，如果支持，则创建一个 UIImagePickerController 对象，设置其 sourceType 属性为 UIImagePickerControllerSourceTypeCamera，即由相机拍摄照片或视频， allowsEditing 属性设置为 YES 表示可编辑。最后将 UIImagePickerController 对象呈现在当前视图上。

2. 自定义相机

有时我们需要自定义相机以实现特殊的拍照和视频录制功能。下面是一个简单的自定义相机的示例代码，该相机功能包括前后摄像头切换、闪光灯控制等。

- (void)setupCaptureSession {
    _captureSession = [[AVCaptureSession alloc] init];
    [_captureSession setSessionPreset:AVCaptureSessionPresetHigh];

    NSError *error = nil;
    AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
    if (videoInput) {
        if ([_captureSession canAddInput:videoInput]) {
            [_captureSession addInput:videoInput];
            _videoDeviceInput = videoInput;
        }
    } else {
        NSLog(@"获取视频输入失败，%@", error);
        return;
    }

    AVCaptureDevice *audioDevice = [[AVCaptureDevice devicesWithMediaType:AVMediaTypeAudio] firstObject];
    AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:&error];
    if (audioInput) {
        if ([_captureSession canAddInput:audioInput]) {
            [_captureSession addInput:audioInput];
        }
    } else {
        NSLog(@"获取音频输入失败，%@", error);
        return;
    }

    AVCapturePhotoOutput *photoOutput = [[AVCapturePhotoOutput alloc] init];
    if ([_captureSession canAddOutput:photoOutput]) {
        [_captureSession addOutput:photoOutput];
        _photoOutput = photoOutput;
    }

    AVCaptureMovieFileOutput *movieOutput = [[AVCaptureMovieFileOutput alloc] init];
    if ([_captureSession canAddOutput:movieOutput]) {
        [_captureSession addOutput:movieOutput];
        _movieOutput = movieOutput;
    }

    dispatch_queue_t captureQueue = dispatch_queue_create("captureQueue", DISPATCH_QUEUE_SERIAL);
    _captureQueue = captureQueue;

    _videoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_captureSession];
    _videoPreviewLayer.frame = self.view.bounds;
    _videoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    [self.view.layer insertSublayer:_videoPreviewLayer atIndex:0];

    [_captureSession startRunning];
}

- (void)switchCamera {
    if (_switchingCamera) {
        return;
    }
    _switchingCamera = YES;

    AVCaptureDevice *currentDevice = [_videoDeviceInput device];
    AVCaptureDevicePosition currentPosition = [currentDevice position];

    AVCaptureDevicePosition targetPosition = AVCaptureDevicePositionUnspecified;
    switch (currentPosition) {
        case AVCaptureDevicePositionFront:
            targetPosition = AVCaptureDevicePositionBack;
            break;

        case AVCaptureDevicePositionBack:
            targetPosition = AVCaptureDevicePositionFront;
            break;

        default:
            break;
    }

    AVCaptureDevice *targetDevice = [self cameraWithPosition:targetPosition];
    AVCaptureDeviceInput *targetInput = [AVCaptureDeviceInput deviceInputWithDevice:targetDevice error:nil];

    [_captureSession beginConfiguration];

    [_captureSession removeInput:_videoDeviceInput];
    if ([_captureSession canAddInput:targetInput]) {
        [_captureSession addInput:targetInput];
        _videoDeviceInput = targetInput;
    } else {
        [_captureSession addInput:_videoDeviceInput];
    }

    [_captureSession commitConfiguration];

    _switchingCamera = NO;
}

- (void)changeFlashMode {
    AVCaptureDevice *device = [self.videoDeviceInput device];
    if (!device.hasFlash) {
        return;
    }

    NSError *error = nil;
    if ([device lockForConfiguration:&error]) {
        if (device.torchMode == AVCaptureTorchModeOff) {
            device.torchMode = AVCaptureTorchModeOn;
            device.flashMode = AVCaptureFlashModeOn;
        } else {
            device.torchMode = AVCaptureTorchModeOff;
            device.flashMode = AVCaptureFlashModeOff;
        }
        [device unlockForConfiguration];
    } else {
        NSLog(@"改变闪光灯状态失败，%@", error);
    }
}

上述代码中，我们使用 AVCaptureSession 类来创建并管理捕获会话。首先创建一个 AVCaptureDeviceInput 对象来获取捕获设备(前/后置摄像头)，并添加到捕获会话中。接着创建 AVCapturePhotoOutput 和 AVCaptureMovieFileOutput 对象来分别处理静态图片和视频的输出。最后创建 AVCaptureVideoPreviewLayer 来实现实时预览。

自定义相机的自定义按钮事件可以按照需求自行添加实现。

3. 图像处理

除了获取静态图片外，iOS 相机管理还可以对相机捕获的图像进行处理，例如调整图像亮度、对比度、饱和度等。下面是一个简单的图像处理示例代码：

- (UIImage *)filterImage:(UIImage *)image {
    CIImage *ciImage = [[CIImage alloc] initWithImage:image];

    CIFilter *filter = [CIFilter filterWithName:@"CIColorControls"];
    [filter setValue:ciImage forKey:@"inputImage"];
    [filter setValue:@(0.5) forKey:@"inputBrightness"];
    [filter setValue:@(0.5) forKey:@"inputContrast"];
    [filter setValue:@(2.0) forKey:@"inputSaturation"];

    CIImage *outputImage = [filter outputImage];
    CIContext *context = [CIContext contextWithOptions:nil];
    CGImageRef imageRef = [context createCGImage:outputImage fromRect:outputImage.extent];

    UIImage *filteredImage = [UIImage imageWithCGImage:imageRef];

    CGImageRelease(imageRef);

    return filteredImage;
}

上述代码中，我们使用了 Core Image 框架来实现对图像的处理。具体实现方法是创建一个 CIImage 对象并使用 CIColorControls 滤镜对其进行处理，然后将处理后的 CIImage 对象转换成 CGImageRef 并创建一个新的 UIImage 对象返回。

4. 总结

以上是 iOS 相机管理的常用操作示例，开发者可根据自己的需求进行相应的处理和扩展。