Make zoom on NSData or on CMSampleBufferRef - ios

Question

I'm developing an iOS application with latest SDK.
This app will work with OpenCV and I have to make zoom on camera but this, it isn't available on iOS SDK, so I think to do it programmatically.
I have to do 'zoom' on every video frame. This is where I have to do it:
#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);
}
Do you know how to make zoom on a NSData or on a CMSampleBufferRef?

Answer 1

One way would be to put your picture into a CGImageRef, choose a square in that picture and draw it again to a normal size. Something like this (though there may be better ways):
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 );