Crops a Picture from AVCaptureSession to the bounds of the AVCaptureVideoPreviewLayer (so Preview = CameraImage)

gistfile1.m

-(UIImage*) cropCameraImage:(UIImage*) original toPreviewLayerBounds:(AVCaptureVideoPreviewLayer*) previewLayer {
    UIImage *ret = nil;
    
    CGRect previewImageLayerBounds = previewLayer.bounds;
    
    // This calculates the crop area.
    // keeping in mind that this works with on an unrotated image (so a portrait image is actually rotated counterclockwise)
    // thats why we use originalHeight to calculate the width
    float originalWidth  = original.size.width;
    float originalHeight = original.size.height;
    
    CGPoint A = previewImageLayerBounds.origin;
    CGPoint B = CGPointMake(previewImageLayerBounds.size.width, previewImageLayerBounds.origin.y);
//    CGPoint C = CGPointMake(self.imageViewTop.bounds.origin.x, self.imageViewTop.bounds.size.height);
    CGPoint D = CGPointMake(previewImageLayerBounds.size.width, previewImageLayerBounds.size.height);
    
    CGPoint a = [previewLayer captureDevicePointOfInterestForPoint:A];
    CGPoint b = [previewLayer captureDevicePointOfInterestForPoint:B];
//    CGPoint c = [previewLayer captureDevicePointOfInterestForPoint:C];
    CGPoint d =[previewLayer captureDevicePointOfInterestForPoint:D];
    
    float posX = floor(b.x * originalHeight);
    float posY = floor(b.y * originalWidth);
    
    CGFloat width = d.x * originalHeight - b.x * originalHeight;
    CGFloat height = a.y * originalWidth - b.y * originalWidth;
    CGRect cropRectangle = CGRectMake(posX, posY, width, height);
    
    // This performs the image cropping.
    CGImageRef imageRef = CGImageCreateWithImageInRect([original CGImage], cropRectangle);
    
    ret = [UIImage imageWithCGImage:imageRef
                              scale:original.scale
                        orientation:original.imageOrientation];
    
    CGImageRelease(imageRef);
    
    return ret;
}

Example call:

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
 // *** some code ***

UIImage *croppedImage = [self cropCameraImage:cameraImage toPreviewLayerBounds:_captureVideoPreviewLayer];
}

Thank you

This snippet was really helpful . Thank you.

Here is a swift version that I created based on this one:
[https://gist.github.com/eddieespinal/a7bb8a97ac3e935af1fb]

Thanks @shexbeer, this helped me a lot too.