AVCaptureSession指定拍摄的图像OBJ-C的iPhone应用程序

Question

您好我想安装AV捕获会话使用iphone的相机捕捉与特定分辨率（如果可能的话，具有特定质量）的图像的分辨率和质量。这里的setupping AV会话代码

// Create and configure a capture session and start it running 
- (void)setupCaptureSession 
{ 
    NSError *error = nil; 

    // Create the session 
    self.captureSession = [[AVCaptureSession alloc] init]; 

    // Configure the session to produce lower resolution video frames, if your 
    // processing algorithm can cope. We'll specify medium quality for the 
    // chosen device. 
    captureSession.sessionPreset = AVCaptureSessionPresetMedium; 

    // Find a suitable AVCaptureDevice 
    NSArray *cameras=[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo]; 
    AVCaptureDevice *device; 
    if ([UserDefaults camera]==UIImagePickerControllerCameraDeviceFront) 
    { 
     device =[cameras objectAtIndex:1]; 
    } 
    else 
    { 
     device = [cameras objectAtIndex:0]; 
    }; 

    // Create a device input with the device and add it to the session. 
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error]; 
    if (!input) 
    { 
     NSLog(@"PANIC: no media input"); 
    } 
    [captureSession addInput:input]; 

    // Create a VideoDataOutput and add it to the session 
    AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init]; 
    [captureSession addOutput:output]; 
    NSLog(@"connections: %@", output.connections); 

    // Configure your output. 
    dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL); 
    [output setSampleBufferDelegate:self queue:queue]; 
    dispatch_release(queue); 

    // Specify the pixel format 
    output.videoSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey]; 


    // If you wish to cap the frame rate to a known value, such as 15 fps, set 
    // minFrameDuration. 


    // Assign session to an ivar. 
    [self setSession:captureSession]; 
    [self.captureSession startRunning]; 
} 

和setSession：

-(void)setSession:(AVCaptureSession *)session 
{ 
    NSLog(@"setting session..."); 
    self.captureSession=session; 
    NSLog(@"setting camera view"); 
    self.previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:session]; 
    //UIView *aView = self.view; 
    CGRect videoRect = CGRectMake(20.0, 20.0, 280.0, 255.0); 
    previewLayer.frame = videoRect; // Assume you want the preview layer to fill the view. 
    [previewLayer setBackgroundColor:[[UIColor grayColor] CGColor]]; 
    [self.view.layer addSublayer:previewLayer]; 
    //[aView.layer addSublayer:previewLayer]; 
} 

和输出方式：

// Delegate routine that is called when a sample buffer was written 
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
    fromConnection:(AVCaptureConnection *)connection 
{ 
    //NSLog(@"captureOutput: didOutputSampleBufferFromConnection"); 

    // Create a UIImage from the sample buffer data 
    self.currentImage = [self imageFromSampleBuffer:sampleBuffer]; 

    //< Add your code here that uses the image > 
} 

// Create a UIImage from sample buffer data 
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer 
{ 
    //NSLog(@"imageFromSampleBuffer: called"); 
    // Get a CMSampleBuffer's Core Video image buffer for the media data 
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
    // Lock the base address of the pixel buffer 
    CVPixelBufferLockBaseAddress(imageBuffer, 0); 

    // Get the number of bytes per row for the pixel buffer 
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer); 

    // Get the number of bytes per row for the pixel buffer 
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
    // Get the pixel buffer width and height 
    size_t width = CVPixelBufferGetWidth(imageBuffer); 
    size_t height = CVPixelBufferGetHeight(imageBuffer); 

    // Create a device-dependent RGB color space 
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 

    // Create a bitmap graphics context with the sample buffer data 
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
    // Create a Quartz image from the pixel data in the bitmap graphics context 
    CGImageRef quartzImage = CGBitmapContextCreateImage(context); 
    // Unlock the pixel buffer 
    CVPixelBufferUnlockBaseAddress(imageBuffer,0); 


    // Free up the context and color space 
    CGContextRelease(context); 
    CGColorSpaceRelease(colorSpace); 

    // Create an image object from the Quartz image 
    UIImage *image = [UIImage imageWithCGImage:quartzImage]; 

    // Release the Quartz image 
    CGImageRelease(quartzImage); 

    return (image); 
} 

一切都非常标准。但是，我应该更改哪些地方和哪些内容来指定拍摄图像的分辨率和质量。请帮助我

Answer 1

参考Apple's guide拍摄静止图像有关部分，其大小，如果你设置一个或另一个预设，你会得到。

你应该改变的参数是captureSession.sessionPreset

Answer 2

尝试这样的事情去哪里Cx和Cy是你的自定义分辨率：

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys: 
           AVVideoScalingModeResizeAspectFill,AVVideoScalingModeKey, 
          AVVideoCodecH264, AVVideoCodecKey, 
          [NSNumber numberWithInt:cx], AVVideoWidthKey, 
          [NSNumber numberWithInt:cx], AVVideoHeightKey, 
          nil]; 
_videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];