重要: 使用する場合:     session.sessionPreset = AVCaptureSessionPresetHigh;プレビュー画像は引き伸ばされません!! 写真をデバイスに保存するとUIImageWriteToSavedPhotosAlbum(image, nil, nil, nil);、画像は正常ですが、プレビューでのみ引き伸ばされます。
AVFoundation を使用して写真をキャプチャしています。
session = [[AVCaptureSession alloc] init];
session.sessionPreset = AVCaptureSessionPresetHigh;
CALayer *viewLayer = vImagePreview.layer;
NSLog(@"viewLayer = %@", viewLayer);
AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
captureVideoPreviewLayer.frame = vImagePreview.bounds;
[vImagePreview.layer addSublayer:captureVideoPreviewLayer];
AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error = nil;
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
if (!input) {
    // Handle the error appropriately.
    NSLog(@"ERROR: trying to open camera: %@", error);
}
[session addInput:input];
stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys: AVVideoCodecJPEG, AVVideoCodecKey, nil];
[stillImageOutput setOutputSettings:outputSettings];
[session addOutput:stillImageOutput];
sessionPreset をAVCaptureSessionPresetPhoto次のように設定しました。
session.sessionPreset = AVCaptureSessionPresetPhoto;
私のキャプチャ方法:
-(void)captureNow {
    AVCaptureConnection *videoConnection = nil;
    for (AVCaptureConnection *connection in stillImageOutput.connections)
    {
        for (AVCaptureInputPort *port in [connection inputPorts])
        {
            if ([[port mediaType] isEqual:AVMediaTypeVideo] )
            {
                videoConnection = connection;
                break;
            }
        }
        if (videoConnection)
        {
            break;
        }
    }
    NSLog(@"about to request a capture from: %@", stillImageOutput);
    [stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error)
     {
         CFDictionaryRef exifAttachments = CMGetAttachment( imageSampleBuffer, kCGImagePropertyExifDictionary, NULL);
         if (exifAttachments)
         {
             // Do something with the attachments.
             NSLog(@"attachements: %@", exifAttachments);
         } else {
             NSLog(@"no attachments");
         }
         NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
         UIImage *image = [[UIImage alloc] initWithData:imageData];
         NSLog(@"%@",NSStringFromCGSize(image.size));
         [self animateUpTheImageWithImage:image];
     }];
}
キャプチャした写真のプレビューを追加する場所:
- (void) animateUpTheImageWithImage:(UIImage*)theImage{
    UIView* preview = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height/*426*/)];
    CALayer *previewLayer = preview.layer;
    AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
    captureVideoPreviewLayer.frame = previewLayer.frame;
    [previewLayer addSublayer:captureVideoPreviewLayer];
    captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspect;
    [self addSubview:preview];
}
その結果、キャプチャした画像が引き伸ばされます。

