Getting a CGImage from CIImage - ios

Question

I have a UIImage which is loaded from a CIImage with:
tempImage = [UIImage imageWithCIImage:ciImage];
The problem is I need to crop tempImage to a specific CGRect and the only way I know how to do this is by using CGImage.
The problem is that in the iOS 6.0 documentation I found this:
CGImage
If the UIImage object was initialized using a CIImage object, the value of the property is NULL.
A. How to convert from CIImage to CGImage?
I'm using this code but I have a memory leak (and can't understand where):
+(UIImage*)UIImageFromCIImage:(CIImage*)ciImage {
CGSize size = ciImage.extent.size;
UIGraphicsBeginImageContext(size);
CGRect rect;
rect.origin = CGPointZero;
rect.size = size;
UIImage *remImage = [UIImage imageWithCIImage:ciImage];
[remImage drawInRect:rect];
UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
remImage = nil;
ciImage = nil;
//
return result;
}

Answer 1

Swift 3, Swift 4 and Swift 5
Here is a nice little function to convert a CIImage to CGImage in Swift.
func convertCIImageToCGImage(inputImage: CIImage) -> CGImage? {
let context = CIContext(options: nil)
if let cgImage = context.createCGImage(inputImage, from: inputImage.extent) {
return cgImage
}
return nil
}
On a desktop or TV, you would typically use:
let ctx = CIContext(options: [.useSoftwareRenderer: false])
let cgImage = ctx.createCGImage(output, from: output.extent)
Many other alternative hint options are available in the core image processor, such as .allowLowPower, .cacheIntermediates, .highQualityDownsample, priorities and so on.
Notes:
CIContext(options: nil) will use a software renderer and can be quite slow. To improve the performance, use CIContext(options: [CIContextOption.useSoftwareRenderer: false]) - this forces operations to run on GPU, and can be much faster.
If you use CIContext more than once, cache it as apple recommends.

Answer 2

See the CIContext documentation for createCGImage:fromRect:
CGImageRef img = [myContext createCGImage:ciImage fromRect:[ciImage extent]];
From an answer to a similar question: https://stackoverflow.com/a/10472842/474896
Also since you have a CIImage to begin with, you could use CIFilter to actually crop your image.

Answer 3

After some googling I found this method which converts a CMSampleBufferRef to a CGImage:
+ (CGImageRef)imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer // Create a CGImageRef from sample buffer data
{
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress(imageBuffer,0); // Lock the image buffer
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0); // Get information of the image
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
CGImageRef newImage = CGBitmapContextCreateImage(newContext);
CGContextRelease(newContext);
CGColorSpaceRelease(colorSpace);
CVPixelBufferUnlockBaseAddress(imageBuffer,0);
/* CVBufferRelease(imageBuffer); */ // do not call this!
return newImage;
}
(but I closed the tab so I don't know where I got it from)