在NSData或CMSampleBufferRef上进行缩放

Question

我正在用最新的SDK开发一个iOS应用程序。

这个应用程序将与OpenCV一起工作，我必须在相机上进行缩放，但这个，它在iOS SDK上不可用，所以我想通过编程来做。

我必须对每个视频帧进行"缩放"。这就是我要做的:

#pragma mark - AVCaptureSession delegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
       fromConnection:(AVCaptureConnection *)connection
{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    /*Lock the image buffer*/
    CVPixelBufferLockBaseAddress(imageBuffer,0);
    /*Get information about the image*/
    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    //size_t stride = CVPixelBufferGetBytesPerRow(imageBuffer);
    //put buffer in open cv, no memory copied
    cv::Mat image = cv::Mat(height, width, CV_8UC4, baseAddress);
    // copy the image
    //cv::Mat copied_image = image.clone();
    _lastFrame = [NSData dataWithBytes:image.data
                                  length:image.elemSize() * image.total()];
    [DataExchanger postFrame];
    /*We unlock the  image buffer*/
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);
}

你知道如何在NSData或CMSampleBufferRef上进行缩放吗?

Answer 1

一种方法是将您的图片放入CGImageRef中，在该图片中选择一个正方形并再次将其绘制为正常大小。像这样(虽然可能有更好的方法):

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);
    CGContextRelease(context);

    CGImageRef smallQuartzImage = CGImageCreateWithImageInRect(quartzImage, CGRectMake(200, 200, 600, 600));
    cv::Mat image(height, width, CV_8UC4 );
    CGContextRef contextRef = CGBitmapContextCreate( image.data, width, height, 8, cvMat.step[0], colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst );
    CGContextDrawImage(contextRef, CGRectMake(0, 0, width, height), smallQuartzImage);
    CGContextRelease( contextRef );
    CGColorSpaceRelease( colorSpace );