iPhone相机拍摄的图像质量

Question

I use iPhone camera to capture images in my iOS APP. AVCaptureVideoDataOutputSampleBufferDelegate is used to get images from iPhone camera. A part of the program is shown below.

AVCaptureDevice *videoDevice = [AVCamViewController deviceWithMediaType:AVMediaTypeVideo preferringPosition:AVCaptureDevicePositionBack];   
AVCaptureDeviceInput *videoDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];   
if (error) { NSLog(@"%@", error); }   
if ([session canAddInput:videoDeviceInput])   
{   
  [session addInput:videoDeviceInput]; [self setVideoDeviceInput:videoDeviceInput];  
   dispatch_async(dispatch_get_main_queue(),    ^{   
   [[(AVCaptureVideoPreviewLayer *)[[self previewView] layer] connection] setVideoOrientation:(AVCaptureVideoOrientation)[self interfaceOrientation]]; });   
}  

The quality of the image taken by AVCaptureVideoDataOutputSampleBufferDelegate and that of the image taken iPhone's camera app are much different. What are the parameters to adjust at AVCaptureVideoDataOutputSampleBufferDelegate to have the same or closer quality as camera app? The two images are attached. The second image is taken by iPhone camera's app. Thanks

EDIT: I can pinpoint where is the problem. I print two images before and after UIImage to cvMat conversion. In UIImage format, the image quality is quite good. After conversion, the quality becomes bad, the color is changed etc.. I attached two images before and after. The first one is before. I used the following code to convert.

- (cv::Mat)cvMatFromUIImage:(UIImage *)image
{
    CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
    CGFloat cols = image.size.width;
    CGFloat rows = image.size.height;

    cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels (color channels + alpha)

    CGContextRef contextRef = CGBitmapContextCreate(cvMat.data,                 // Pointer to  data
                                                    cols,                       // Width of bitmap
                                                    rows,                       // Height of bitmap
                                                    8,                          // Bits per component
                                                    cvMat.step[0],              // Bytes per row
                                                    colorSpace,                 // Colorspace
                                                    kCGImageAlphaNoneSkipLast |
                                                    kCGBitmapByteOrderDefault); // Bitmap info flags

    CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
    CGContextRelease(contextRef);

    return cvMat;
}

Writing the image to jpg file shouldn't be a problem. But this is the code to save image

- (void) saveImage:(std::string)name img:(Mat)gray{
    //Print
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *filePath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%3s.jpg", name.c_str()]];
    const char* cPath = [filePath cStringUsingEncoding:NSMacOSRomanStringEncoding];
    const cv::String newPaths = (const cv::String)cPath;

    //Save as Bitmap to Documents-Directory
    cv::imwrite(newPaths, gray);
}

Conversion code from UIImage to cvMat is quite standard and why it has this problem?

Answer 1

您可以使用sessionPreset控制捕获输入信号的质量阅读更多在这里